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Authors: Nathalie Kuhn, Macarena Arellano, Claudio Ponce, Christian Hodar, Francisco Correa, Salvatore Multari, Stefan Martens, Esther Carrera, José Manuel Donoso and Lee A. Meisel
Journal of Plant Growth Regulation (2024)
Abstract: "Abscisic acid (ABA) is a plant hormone that plays a key role in the ripening process of non-climacteric fruits, triggering pigment production, fruit softening, and sugar accumulation. Transcriptional studies show that ABA modifies the expression of several ripening-related genes, but epigenetic effects of ABA during this process are lacking. Therefore, this work aimed to perform transcriptomic and DNA methylation analyses of fruit samples treated with ABA during the fruit ripening process in the non-climacteric sweet cherry model. RNA-seq analyses revealed an overrepresentation of transcripts annotated in functional categories related to ABA response, secondary metabolism, and sugar synthesis during fruit ripening. In contrast, Whole Genome Bisulfite Sequencing (WGBS) analyses revealed DNA hypomethylation in the 5′UTR region of genes related to carotene catabolism. Transcriptional and epigenetic regulation of genes encoding xyloglucan enzymes, associated with cell wall modifications, were also detected. ABA treatment enhanced fruit color development and the accumulation of ripening markers, including carotenoids and several anthocyanins. Gene Ontology analysis in the RNA-seq of ABA-treated fruits revealed expression variations in genes encoding members of the Aux/IAA and ARF families. In the WGBS analysis, genes encoding enzymes for cytokinin biosynthesis had differential DNA methylation after the ABA treatment. Our work identified ABA-modulated factors at the genetic and epigenetic levels, suggesting complex hormone networks controlling non-climacteric sweet cherry fruit ripening."
Authors: Shenhua Ye, Yingying Huang, Tiantian Ma, Xiaowei Ma, Rihui Li, Jinxiong Shen and Jing Wen.
Plant Physiology (2024)
Abstract: "Zeaxanthin epoxidase (ZEP) is a key enzyme that catalyzes the conversion of zeaxanthin to violaxanthin in the carotenoid and abscisic acid (ABA) biosynthesis pathways. The rapeseed (Brassica napus) genome has 4 ZEP (BnaZEP) copies that are suspected to have undergone subfunctionalization, yet the 4 genes’ underlying regulatory mechanisms remain unknown. Here, we genetically confirmed the functional divergence of the gene pairs BnaA09.ZEP/BnaC09.ZEP and BnaA07.ZEP/BnaC07.ZEP, which encode enzymes with tissue-specific roles in carotenoid and ABA biosynthesis in flowers and leaves, respectively. Molecular and transgenic experiments demonstrated that each BnaZEP pair is transcriptionally regulated via ABA-responsive element–binding factor 3 s (BnaABF3s) and BnaMYB44s as common and specific regulators, respectively. BnaABF3s directly bound to the promoters of all 4 BnaZEPs and activated their transcription, with overexpression of individual BnaABF3s inducing BnaZEP expression and ABA accumulation under drought stress. Conversely, loss of BnaABF3s function resulted in lower expression of several genes functioning in carotenoid and ABA metabolism and compromised drought tolerance. BnaMYB44s specifically targeted and repressed the expression of BnaA09.ZEP/BnaC09.ZEP but not BnaA07.ZEP/BnaC07.ZEP. Overexpression of BnaA07.MYB44 resulted in increased carotenoid content and an altered carotenoid profile in petals. Additionally, RNA-seq analysis indicated that BnaMYB44s functions as a repressor in phenylpropanoid and flavonoid biosynthesis. These findings provide clear evidence for the subfunctionalization of duplicated genes and contribute to our understanding of the complex regulatory network involved in carotenoid and ABA biosynthesis in B. napus."
Authors: Zoltán Tolnai, Himani Sharma and Vilmos Soós.
Journal of Experimental Botany (2024)
Abstract: "Strigolactones and ABA are apocarotenoid-derived plant hormones. Their biosynthesis starts with the conversion of trans-carotenes into cis forms, which serve as direct precursors. Iron-containing DWARF27 isomerases were shown to catalyse or contribute to the trans/cis conversions of these precursor molecules. D27 converts trans-β-carotene into 9-cis-β-carotene which is the first committed step in strigolactone biosynthesis. Recent studies found that its paralog, D27-LIKE1 also catalyses this conversion. A crucial step in ABA biosynthesis is the oxidative cleavage of 9-cis-violaxanthin and/or 9-cis-neoxanthin which are formed from their trans isomers by unknown isomerases. Several lines of evidence point out that D27-like proteins directly, or indirectly contribute to 9-cis-violaxanthin conversion and eventually, ABA biosynthesis. Apparently, the diversity of D27-like enzymatic activity is essential for the optimization of cis/trans ratios, and hence, act to maintain apocarotenoid precursor pools. In this review we discuss the functional divergence and redundancy of D27 paralogs and their potential direct contribution to ABA precursor biosynthesis. We provide updates on their gene expression regulation and alleged Fe-S cluster binding feature. Finally, we conclude that the functional divergence of these paralogs is not fully understood and we give an outlook on potential directions in research."
Authors: Jeanne Braat, Meryl Jaonina, Pascale David, Maïté Leschevin, Bertrand Légeret, Stefano D’Alessandro, Frédéric Beisson and Michel Havaux.
PNAS Nexus (2023)
Abstract: "New regulatory functions in plant development and environmental stress responses have recently emerged for a number of apocarotenoids produced by enzymatic or non-enzymatic oxidation of carotenoids. β-cyclocitric acid (β-CCA) is one such compound derived from β-carotene which triggers defense mechanisms leading to a marked enhancement of plant tolerance to drought stress. We show here that this response is associated with an inhibition of root growth affecting both root cell elongation and division. Remarkably, β-CCA selectively induced cell cycle inhibitors of the SIAMESE-RELATED (SMR) family, especially SMR5, in root tip cells. Overexpression of the SMR5 gene in Arabidopsis induced molecular and physiological changes that mimicked in large part the effects of β-CCA. In particular, the SMR5 overexpressors exhibited an inhibition of root development and a marked increase in drought tolerance which is not related to stomatal closure. SMR5 up-regulation induced changes in gene expression that strongly overlapped with the β-CCA-induced transcriptomic changes. Both β-CCA and SMR5 led to a down-regulation of many cell cycle activators (cyclins, cyclin-dependent kinases) and a concomitant up-regulation of genes related to water deprivation, cellular detoxification and biosynthesis of lipid biopolymers such as suberin and lignin. This was correlated with an accumulation of suberin lipid polyesters in the roots and a decrease in non-stomatal leaf transpiration. Taken together, our results identify the β-CCA- and drought-inducible SMR5 gene as a key component of a stress signaling pathway that reorients root metabolism from growth to multiple defense mechanisms leading to drought tolerance."
Authors: Yanna Xu, Congjun You, Changbin Xu, Chaofan Zhang, Xiaoli Hu, Xiaolong Li, Haijie Ma, Jinli Gong and Xuepeng Sun.
Postharvest Biology and Technology (2024)
Highlights: • Skin coloration of tomato fruit responds differentially to red and blue light. • Both lights promote biosynthesis of carotenoids and phytohormones. • Gene modules associated with carotenoid and hormone metabolism were identified. • Transcription factors as key regulators of the modules were uncovered. • A working model was proposed to depict the light regulation of fruit coloration.
Abstract: "Understanding how light regulates pigment composition and accumulation is crucial for postharvest management of fruit quality and nutritional value. In this study, we investigated the influence of light quality, specifically the blue and red lights, on coloration of tomato fruit. We show that both lights expedite the progress of skin coloration in tomato fruit by promoting chlorophyll degradation, stimulating carotenoid biosynthesis, accelerating plastid conversion, and enhancing plant hormone (i.e., abscisic acid and ethylene) biosynthesis. However, red light shows higher efficiency in inducing color transition compared with blue light. Gene expression network analysis unraveled several modules that are associated with carotenoid metabolism and hormone biosynthesis in response to light treatments, among which the transcription factors including WRKY20, MYB12, ARR11, NAC16, bHLH46, ZNF69, and MYB58 were identified as potential key regulators. Collectively, our data provide new threads on the regulation of fruit coloration by light quality and highlight the potential utility of red LED treatment to improve the color and quality of tomato fruit."
Authors: Richard V. Espley and Laura Jaakola.
Plant, Cell & Environment (2023)
Abstract: "For many fruit crops, the colour of the fruit outwardly defines its eating quality. Fruit pigments provide reproductive advantage for the plant as well as providing protection against unfavourable environmental conditions and pathogens. For consumers these colours are considered attractive and provide many of the dietary benefits derived from fruits. In the majority of species, the main pigments are either carotenoids and/or anthocyanins. They are produced in the fruit as part of the ripening process, orchestrated by phytohormones and an ensuing transcriptional cascade, culminating in pigment biosynthesis. Whilst this is a controlled developmental process, the production of pigments is also attuned to environmental conditions such as light quantity and quality, availability of water and ambient temperature. If these factors intensify to stress levels, fruit tissues respond by increasing (or ceasing) pigment production. In many cases, if the stress is not severe, this can have a positive outcome for fruit quality. Here, we focus on the principal environmental factors (light, temperature and water) that can influence fruit colour."
Authors: Mengjie Fu, Fenfen Li, Shengen Zhou, Pengyu Guo, Yanan Chen, Qiaoli Xie, Guoping Chen and Zongli Hu.
Journal of Experimental Botany (2023)
Abstract: "Trihelix proteins are plant-specific transcription factors that play crucial roles in plant development and stress responses. However, the involvement of trihelix proteins in fruit ripening and transcriptional regulatory mechanisms remains largely unclear. In this study, we cloned a trihelix gene SlGT31, whose relative expression was significantly induced by the application of exogenous ethylene but repressed by 1-methylcyclopropene (1-MCP). Suppression of SlGT31 resulted in delayed fruit ripening, decreased accumulation of total carotenoids and ethylene content, and inhibition of relative expression of genes related to ethylene and fruit ripening. Conversely, the opposite results were observed in SlGT31-overexpression lines. Yeast one-hybrid and dual-luciferase assays suggested that SlGT31 could bind to the promoters of two key ethylene biosynthesis genes ACO1 and ACS4. These results indicate that SlGT31 may act as a positive modulator during fruit ripening."
Authors: Miguel Ezquerro, Esteban Burbano-Erazo and Manuel Rodriguez-Concepcion.
Plant Physiology (2023)
One-sentence summary: The main flux-controlling step of the carotenoid pathway in tomato is catalyzed by a small family of enzymes that differentially contribute to the biosynthesis of carotenoids and derived hormones.
Abstract: "Carotenoids are plastidial isoprenoids required for photosynthesis and phytohormone production in all plants. In tomato (Solanum lycopersicum), carotenoids also provide color to flowers and ripe fruit. Phytoene synthase (PSY) catalyzes the first and main flux-controlling step of the carotenoid pathway. Three genes encoding PSY isoforms are present in tomato, PSY1 to PSY3. Mutants have shown that PSY1 is the isoform providing carotenoids for fruit pigmentation, but it is dispensable in photosynthetic tissues. No mutants are available for PSY2 or PSY3, but their expression profiles suggest a main role for PSY2 in leaves and PSY3 in roots. To further investigate isoform specialization with genetic tools, we created gene-edited lines defective in PSY1 and PSY2 in the MicroTom background. The albino phenotype of lines lacking both PSY1 and PSY2 confirmed that PSY3 does not contribute to carotenoid biosynthesis in shoot tissues. Our work further showed that carotenoid production in tomato shoots relies on both PSY1 and PSY2 but with different contributions in different tissues. PSY2 is the main isoform for carotenoid biosynthesis in leaf chloroplasts, but PSY1 is also important in response to high light. PSY2 also contributes to carotenoid production in flower petals and, to a lesser extent, fruit chromoplasts. Most interestingly, our results demonstrate that fruit growth is controlled by abscisic acid (ABA) specifically produced in the pericarp from PSY1-derived carotenoid precursors, whereas PSY2 is the main isoform associated with ABA synthesis in seeds and salt-stressed roots."
Authors: Wei Wu, Ning-jing Sun, Yang Xu, Yu-tong Chen, Xiao-fen Liu, Li-yu Shi, Wei Chen, Qing-gang Zhu, Bang-chu Gong, Xue-ren Yin and Zhen-feng Yang.
Plant Physiology (2023)
Abstract: "As the harvest season of most fruit is concentrated, fruit maturation manipulation is essential for the fresh fruit industry to prolong sales time. Gibberellin (GA), an important phytohormone necessary for plant growth and development, has also shown a substantial regulatory effect on fruit maturation; however, its regulatory mechanisms remain inconclusive. In this research, preharvest GA3 treatment effectively delayed fruit maturation in several persimmon (Diospyros kaki) cultivars. Among the proteins encoded by differentially expressed genes, two transcriptional activators (NAC TRANSCRIPTION FACTOR DkNAC24 and ETHYLENE RESPONSIVE FACTOR DkERF38) and a repressor (MYB-LIKE TRANSCRIPTION FACTOR DkMYB22) were direct regulators of GERANYLGERANYL DIPHOSPHATE SYNTHASE DkGGPS1, LYSINE HISTIDINE TRANSPORTER DkLHT1, and FRUCTOSE-BISPHOSPHATE ALDOLASE DkFBA1 respectively, resulting in the inhibition of carotenoid synthesis, outward transport of an ethylene precursor, and consumption of fructose and glucose. Thus, the present study not only provides a practical method to prolong the persimmon fruit maturation period in various cultivars, but also provides insights into the regulatory mechanisms of GA on multiple aspects of fruit quality formation at the transcriptional regulation level."
Authors: Abrar Felemban, Juan C. Moreno, Jianing Mi, Shawkat Ali, Arjun Sham, Synan F. AbuQamar and Salim Al-Babili.
bioRxiv (2023)
Abstract: "Carotenoids are isoprenoid pigments vital for photosynthesis. Moreover, they are the precursor of apocarotenoids that include the phytohormones abscisic acid (ABA) and strigolactones (SLs), and retrograde signaling molecules and growth regulators, such as β-cyclocitral and zaxinone. The apocarotenoid β-ionone (β-I) was previously reported to exert antimicrobial effects. Here, we showed that the application of this scent to Arabidopsis plants at micromolar concentrations caused a global reprogramming of gene expression, affecting thousands of transcripts involved in stress tolerance, growth, hormone metabolism, pathogen defense and photosynthesis. These changes, along with modulating the levels of the phytohormones ABA, jasmonic acid and salicylic acid, led to enhanced Arabidopsis resistance to Botrytis cinerea (B.c.), one of the most aggressive and widespread pathogenic fungi affecting numerous plant hosts and causing severe losses of postharvest fruits. Pre-treatment of tobacco and tomato plants with β-I followed by inoculation with B.c. confirms the conserved effect of β-I and induced immune responses in leaves and fruits. Moreover, there was reduced susceptibility to B.c. in LYCOPENE β-CYCLASE- expressing tomato fruits possessing elevated levels of the endogenous β-I, indicating beneficial biological activities of this compound in planta. Our work unraveled β-I as a further carotenoid-derived regulatory metabolite and opens up new possibilities to control B.c. infection by establishing this natural volatile as an environmentally friendly bio-fungicide."
Author: Divya Mishra.
Plant Physiology (2023)
Excerpts: "In this issue of Plant Physiology, Gambhir et al. (2023) investigated the underlying mechanism of MG detoxification through the help of glyoxalase enzymes in fruit development. To establish the role of MG in fruit ripening, they treated wild-type (WT) tomatoes with exogenous MG, which slowed down ripening compared to the control. The ripening-deficient rin mutants were yellow, similar to the WT tomato infiltrated with MG. These observations led to a question: what is the mechanism of lowering MG concentration during tomato fruit development? MG is a toxic chemical that is converted into a non-toxic chemical by the action of the glyoxalase enzyme (Ling et al., 2021)." "To understand the interaction of ethylene with methylglyoxal, Gambhir et al. performed expression analysis of genes related to ethylene biosynthetic pathways and found that ethylene biosynthesis is compromised. They also observed lower methionine levels, a precursor of ethylene biosynthesis, in the SlGLYI4-silenced fruits. Moreover, even the external methionine supply to SlGLYI4-silenced fruits failed to induce ethylene production, indicating that silencing of SlGLYI4 resulted in the MG accumulation that might glycate the enzyme responsible for catalyzing the ethylene biosynthesis pathway. Collectively, the study sheds light on the regulatory mechanism of SlGLYI4-mediated detoxification of MG during fruit ripening that would help in manipulating traits contributing to fruit quality and shelf life (Figure 1).
Authors: Fanliang Meng, Haoran Liu, Songshen Hu, Chengguo Jia, Min Zhang, Songwen Li, Yuanyuan Li, Jiayao Lin, Yue Jian, Mengyu Wang, Zhiyong Shao, Yuanyu Mao, Lihong Liu and Qiaomei Wang.
Journal of Integrative Plant Biology (2023)
Abstract: "The plant hormone ethylene is essential for climacteric fruit ripening, although it is unclear how other phytohormones and their interactions with ethylene might affect fruit ripening. Here, we explored how brassinosteroids (BRs) regulate fruit ripening in tomato (Solanum lycopersicum) and how they interact with ethylene. Exogenous BR treatment and increased endogenous BR contents in tomato plants overexpressing the BR biosynthetic gene SlCYP90B3 promoted ethylene production and fruit ripening. Genetic analysis indicated that the BR signaling regulators Brassinazole-resistant1 (SlBZR1) and BRI1-EMS-suppressor1 (SlBES1) act redundantly in fruit softening. Knocking out SlBZR1 inhibited ripening through transcriptome reprogramming at the onset of ripening. Combined transcriptome deep sequencing and chromatin immunoprecipitation followed by sequencing identified 73 SlBZR1-repressed targets and 203 SlBZR1-induced targets involving major ripening-related genes, suggesting that SlBZR1 positively regulates tomato fruit ripening. SlBZR1 directly targeted several ethylene and carotenoid biosynthetic genes to contribute to the ethylene burst and carotenoid accumulation to ensure normal ripening and quality formation. Furthermore, knockout of Brassinosteroid-insensitive2 (SlBIN2), a negative regulator of BR signaling upstream of SlBZR1, promoted fruit ripening and carotenoid accumulation. Taken together, our results highlight the role of SlBZR1 as a master regulator of tomato fruit ripening with potential for tomato quality improvement and carotenoid biofortification."
Authors: S. Kondo, H. Tomiyama, R. Oda, T. Saito, K. Ohkawa, H. Ohara, S. Aramaki, T. Inoue and T. Otsuka
Plant Growth Regulation (2023)
Abstract: "We have previously reported that the application of- used as isoprothiolane (IPT), a fungicide against rice blast- 20 to 30 days before harvest improved peel color in satsuma mandarin fruit (Citrus unshiu Marcow). However, the mechanism by which IPT improves peel coloration is not yet fully understood. This study examined the effects of IPT on plant hormones such as gibberellic acid (GA) and abscisic acid (ABA), and carotenoid accumulation. Whole trees were treated with IPT at 25 days before harvest. Concentrations of gibberellic acid-1 (GA1) and GA4 in the flavedo of IPT-treated trees were significantly decreased at 5 days after treatment (DAT) compared to the untreated control. The expressions of CitGA20ox1 in IPT-treated flavedo were lower than those in the untreated controls at 5 and 25 DAT. The CitGA3ox expressions in IPT-treated flavedo were lower than those in the untreated control at 5 DAT. ABA concentrations in IPT-treated flavedo were significantly higher than those in the untreated control at 25 DAT. The concentrations of β-cryptoxanthin in IPT-treated flavedo were higher than those in the untreated control at 25 DAT. The chlorophyll concentrations of IPT-treated flavedo were lower than those in the untreated control at 5 and 20 DAT. These results suggest that IPT advances β-cryptoxanthin accumulation through the regulation of endogenous GA1 and GA4 based on the inhibition of CitGA20ox1 and CitGA3ox expressions. It is possible that IPT can be utilized to improve coloration in other citrus fruit."
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Authors: Dongjie Jia, Yuchen Li, Kun Jia, Benchang Huang, Qingyuan Dang, Huimin Wang, Xinyuan Wang, Chunyu Li, Yugang Zhang, Jiyun Nie and, Yongbing Yuan.
Plant Physiology (2024)
One-sentence summary: Abscisic acid activates a TF module that regulates apple color by activating the major carotenoid biosynthesis genes.
Abstract: "Carotenoids are major pigments contributing to fruit coloration. We previously reported that the apple (Malus domestica Borkh.) mutant fruits of “Beni Shogun” and “Yanfu 3” show a marked difference in fruit coloration. However, the regulatory mechanism underlying this phenomenon remains unclear. In this study, we determined that carotenoid is the main factor influencing fruit flesh color. We identified an R1-type MYB transcription factor (TF), MdMYBS1, which was found to be highly associated with carotenoids and abscisic acid (ABA) contents of apple fruits. Overexpression of MdMYBS1 promoted, and silencing of MdMYBS1 repressed, β-branch carotenoids synthesis and ABA accumulation. MdMYBS1 regulates carotenoid biosynthesis by directly activating the major carotenoid biosynthetic genes encoding phytoene synthase (MdPSY2-1) and lycopene β-cyclase (MdLCYb). 9-cis-epoxycarotenoid dioxygenase 1 (MdNCED1) contributes to ABA biosynthesis, and MdMYBS1 enhances endogenous ABA accumulation by activating the MdNCED1 promoter. In addition, the basic leucine zipper domain TF ABSCISIC ACID-INSENSITIVE5 (MdABI5) was identified as an upstream activator of MdMYBS1, which promotes carotenoid and ABA accumulation. Furthermore, ABA promotes carotenoid biosynthesis and enhances MdMYBS1 and MdABI5 promoter activities. Our findings demonstrate that the MdABI5–MdMYBS1 cascade activated by ABA regulates carotenoid-derived fruit coloration and ABA accumulation in apple, providing avenues in breeding and planting for improvement of fruit coloration and quality."
Authors: James Giovannoni, Yao Chen, Xin Wang, Vincent Colantonio, Tara Fish, Jie Ye, Theodore Thannhauser, Zhibiao Ye, Mingchun Liu, Yongsheng Liu and Zhangjun Fei.
Research Square (2024)
Abstract: "Ripening is crucial for the development of fleshy fruits that release their seeds following consumption by frugivores and are important contributors to human health and nutritional security. Many genetic ripening regulators have been identified, especially in the model system tomato, yet more remain to be discovered and integrated into comprehensive regulatory models. Most tomato ripening genes have been studied in pericarp tissue, though recent evidence indicates that locule tissue is a site of early ripening-gene activities. Here we identified and functionally characterized an Ethylene Response Factor gene, SlERF.D6, by investigating tomato transcriptome data throughout plant development, emphasizing genes elevated in the locule during fruit development and ripening. SlERF.D6loss-of-function mutants resulting from CRISPR/Cas9 gene editing delayed ripening initiation and carotenoid accumulation in both pericarp and locule tissues. Transcriptome analysis of lines altered in SlERF.D6 expression revealed multiple classes of altered genes including ripening regulators, in addition to carotenoid, cell wall and ethylene pathway genes, suggesting comprehensive ripening control. Distinct regulatory patterns in pericarp versus locule tissues were observed indicating tissue-specific activity of this transcription factor. Analysis of SlERF.D6 interaction with target promoters revealed an AP2/ERF transcription factor (SlDEAR2) as a target of SlERF.D6. Furthermore, we show that a third transcription factor gene, SlTCP12, is a target of SlDEAR2, presenting a tri-component module of ripening control."
Authors: Quan Sun, Zhengchen He, Ranran Wei, Yin Zhang, Junli Ye, Lijun Chai, Zongzhou Xie, Wenwu Guo, Juan Xu, Yunjiang Cheng, Qiang Xu and Xiuxin Deng.
Plant Biotechnology Journal (2023)
Abstract: "Carotenoids contribute to fruit coloration and are valuable sources of provitamin A in the human diet. Abscisic acid (ABA) plays an essential role in fruit coloration during citrus fruit ripening, but little is known about the underlying mechanisms. Here, we identified a novel bZIP transcription activator called CsbZIP44, which serves as a central regulator of ABA-mediated citrus carotenoid biosynthesis. CsbZIP44 directly binds to the promoters of four carotenoid metabolism-related genes (CsDXR, CsGGPPs, CsBCH1 and CsNCED2) and activates their expression. Furthermore, our research indicates that Cashback, a positive regulator of ABA and carotenoid-driven processes, activates the expression of CsbZIP44 by binding to its promoter. Additionally, CsHB5 interacts with CsbZIP44 to form a transcriptional regulatory module CsHB5-CsbZIP44, which is responsive to ABA induction and promotes carotenoid accumulation in citrus. Interestingly, we also discover a positive feedback regulation loop between the ABA signal and carotenoid biosynthesis mediated by the CsHB5-CsbZIP44 transcriptional regulatory module. Our findings show that CsHB5-CsbZIP44 precisely modulates ABA signal-mediated carotenoid metabolism, providing an effective strategy for quality improvement of citrus fruit and other crops."
Authors: Abdugaffor Ablazov, Muhammad Jamil, Imran Haider, Jian You Wang, Vanessa Melino, Moez Maghrebi, Gianpiero Vigani, Kit Xi Liew, Pei-Yu Lin, Guan-Ting Chen, Hendrik NJ Kuijer, Lamis Berqdar, Teresa Mazzarella, Valentina Fiorilli, Luisa Lanfranco, Xiongjie Zheng, Nai-Chiang Dai, Ming-Hsin Lai, Yue-Ie Caroline Hsing, Mark Tester, Ikram Blilou and Salim Al-Babili.
bioRxiv (2023)
Abstract: "The rice Zaxinone Synthase (ZAS) gene encodes a carotenoid cleavage dioxygenase (CCD) that forms the apocarotenoid growth regulator zaxinone. Here, we generated and characterized constitutive ZAS-overexpressing rice lines, to better understand ZAS role in determining zaxinone content and regulating growth and architecture. ZAS overexpression enhanced endogenous zaxinone level, promoted root growth and meristem size, and increased the number of productive tillers, leading to an up to 30% higher grain yield per plant. Hormone analysis revealed a decrease in strigolactone (SL) content, which we confirmed by rescuing the high-tillering phenotype through application of a SL analog. Metabolomics analysis revealed that ZAS overexpressing plants accumulate higher amounts of monosaccharide sugars, in line with transcriptome analysis. Moreover, transgenic plants showed higher carbon (C) assimilation rate and elevated root phosphate, nitrate and sulfate level, enhancing the tolerance towards low phosphate (Pi) and indicating a generally better nutrient uptake. Our study shows that ZAS regulates hormone homeostasis and a combination of physiological processes to promote growth and grain yield, which makes this gene an excellent candidate for sustainable crop improvement."
Authors: Kang Xu, Haoran Zeng, Emi Yumoto, Masashi Asahina, Ken-ichiro Hayashi, Hidehiro Fukaki, Hisashi Ito and Masaaki K. Watahiki.
bioRxiv (2023)
Abstract: "Carotenoids support plant developmental activities as photosynthesis and photoprotective pigments, and also provide precursors for production of phytohormone abscisic acid and strigolactones, or bioactive apocarotenoids. Herein, we examined the role of carotenoid as a source of apocarotenoids, which control endogenous auxin levels and plant root architecture. Inhibiting β-carotene biosynthesis by phytoene desaturase (PDS) inhibitor fluridone suppresses root growth, consequently inducing lateral root growth. PDS was confirmed to be the target of fluridone via the expression of the fluridone-insensitive trait 35S::mHvPDS in an Arabidopsis plant. Inhibiting β-carotene biosynthesis elevated endogenous auxin levels and activated auxin signaling, thereby suppressing root growth. In addition, the root growth of the auxin-deficient mutant yucQ was partially restored via fluridone treatment. These results indicate that suppressing PDS activity increases endogenous auxin levels and suppresses root growth. Conversely, the carotenoid pool indirectly suppresses endogenous auxin levels. Exogenous application of retinal, apocarotenoid derived from β-carotene, complemented fluridone-mediated root growth inhibition and partially recovered auxin-mediated growth inhibition. Moreover, retinal inhibited the induction of the auxin-inducible reporter pIAA19::ElucPEST, indicating an antagonistic effect of retinal on endogenous auxin levels. Interestingly, the auxin-deficient mutants wei2 wei7 and yucQ accumulated more β-carotene compared with the wild type. The expression of CCDs, which converts β-carotene into apocarotenoids, is auxin-inducible and increases following fluridone treatment. These results indicate feedback regulation during apocarotenoid biosynthesis in plant tissue. Thus, we conclude carotenoid regulates auxin levels and response, and this regulation is intermediated by apocarotenoid retinal."
Authors: Gang Ma, Lancui Zhang, Kan Murakami, Masaki Yahata and Masaya Kato.
The Horticulture Journal (2023)
Abstract: ‘Miyagawa-wase’ (Citrus unshiu Marcow.), an early-season citrus variety, is rich in multiple nutrients and widely consumed in Japan. In ‘Miyagawa-wase’, when the pulp reaches maturity and is ready to eat, the peel is still a greenish color because of the relatively high temperature in the harvest season. In this study, to improve the coloration of ‘Miyagawa-wase’ peel, we treated the fruit with 1-naphthaleneacetic acid (NAA) after harvest. The results showed that postharvest treatment with NAA was effective to induce chlorophyll degradation and carotenoid accumulation in ‘Miyagawa-wase’ peel during storage. In the NAA treatment, the reduction in the chlorophyll contents after harvest was in parallel with decreases in the expression of chlorophyll biosynthetic genes (CitGGDR, CitCHLH, CitCHL27, CitPORA, and CitCAO) and an increase in chlorophyll degradation gene CitPPH. The contents of the major carotenoids, β-cryptoxanthin and 9-cis-violaxanthin, were increased by the NAA treatment through upregulation of the expression of carotenoid biosynthetic genes (CitPSY, CitPDS, CitZDS, CitLCYb2, and CitHYb) after harvest. In addition, it was found that the positive effect on degreening in the NAA treatment was inhibited by the ethylene antagonist 1-MCP. In the combination treatment using NAA and 1-MCP, the total chlorophyll content was much higher, while the contents of β-cryptoxanthin and 9-cis-violaxanthin were lower compared with NAA treatment alone, indicating that the acceleration of degreening by NAA may be caused by ethylene. The results presented in this study suggest that postharvest NAA treatment is an effective method for improving the peel coloration in early-season citrus varieties."
Authors: Muhammad Jamil, Pei-Yu Lin, Lamis Berqdar, Jian You Wang, Ikuo Takahashi, Tsuyoshi Ota, Noor Alhammad, Guan-Ting Erica Chen, Tadao Asami and Salim Al-Babili.
Biomolecules (2023)
Abstract: "The apocarotenoid zaxinone is a recently discovered regulatory metabolite required for proper rice growth and development. In addition, zaxinone and its two mimics (MiZax3 and MiZax5) were shown to have a remarkable growth-promoting activity on crops and a capability to reduce infestation by the root parasitic plant Striga through decreasing strigolactone (SL) production, suggesting their potential for application in agriculture and horticulture. In the present study, we developed a new series of MiZax via structural modification of the two potent zaxinone mimics (MiZax3 and MiZax5) and evaluated their effect on plant growth and Striga infestation. In general, the structural modifications to MiZax3 and MiZax5 did not additionally improve their overall performance but caused an increase in certain activities. In conclusion, MiZax5 and especially MiZax3 remain the likely most efficient zaxinone mimics for controlling Striga infestation."
Authors: Yuanda Lv, Shuang Ren, Bo Wu, Caizhong Jiang, Bo Jiang, Birong Zhou, Guangyan Zhong, Yun Zhong and Huaxue Yan.
Tree Physiology (2023)
Abstract: "Previous studies have shown that abscisic acid and ethylene are involved in pulp maturation and peel coloration in the nonclimacteric citrus fruits. There are also signs indicating that other plant hormones may play some roles in citrus fruit ripening. In this study, we compared profiles of genome-wide gene expression, and changes in hormones and peel pigments between fruits of Shatangju mandarin (Citrus reticulata Blanco, designated WT) and its natural mutant, Yuenongwanju (designated MT). The MT fruit mature approximately two months later than the WT fruit. Significant differences in fruit diameter, total soluble solids, titratable acid content, chlorophylls and carotenoids were detected between the fruits of the two genotypes at the sampled time points. Genome-wide transcriptome profiling showed that many genes involved in auxin and ABA metabolism and/or signaling pathways were differentially expressed between the MT and the WT fruits. Importantly, the expression of CrYUCCA8 was significantly lower and the expression of CrNCED5 was significantly higher in WT than in MT fruits at 230 and 250 DPA, respectively. In addition, the IAA level in the MT fruit was significantly higher than that in the WT counterpart, whereas a significantly lower level of ABA was detected in the mutant. Treatment of the WT fruit with exogenous IAA significantly delayed fruit maturation. Our results provide experimental evidence supporting the notion that auxin is a negative regulator of fruit maturation in citrus."
Authors: Hongli Li, Gangshuai Liu and Daqi Fu.
Postharvest Biology and Technology (2023)
Highlights: • Tomato serves as the model plant for studying fruit quality formation. • Fruit quality formation is regulated by a series of transcription factors. • Interactions between transcription factors related to fruit quality.
Abstract: "Tomato serves as the model plant for studying fruit ripening and quality formation including pigment, texture, flavor, aroma and nutrition. The ripening of tomato fruit results from the selective expression of ripening-related genes, which are strictly regulated by transcription factors (TFs), such as RIPENING INHIBITOR (RIN), NON-RIPENING (NOR) and COLORLESS NON-RIPENING (CNR). Understanding the transcriptional network has important biological significance for the fruit ripening regulation, which can help improve fruit quality and commodity value, and improve the utilization of agricultural resources. The molecular mechanism of TF control, a redundant regulatory network, has been extensively studied thanks to advancements in scientific research technologies. Here, we focus on the synergistic or antagonistic regulation of TFs in tomato fruit ripening, including the relationship between TFs and the regulatory patterns of ripening-related target genes, which is supported by sufficient evidence."
Authors: Jianyan Zeng, Dan Yao, Ming Luo, Lingli Ding, Yi Wang, Xingying Yan, Shu'e Ye, Chuannan Wang, Yiping Wu, Jingyi Zhang, Yaohua Li, Lingfang Ran, Yonglu Dai, Yang Chen, Fanlong Wang, Hanyan Lai, Nian Liu, Nianjuan Fang, Yan Pei and Yuehua Xiao.
The Crop Journal (2023)
Abstract: "Cotton fiber is a raw material for the global textile industry and fiber quality is essential to its industrial application. Carotenoids are plant secondary metabolites that may serve as dietary components, regulate light harvesting, and scavenge reactive oxygen species. Although carotenoids accumulate predominantly in rapidly elongating cotton fibers, their roles in cotton fiber development remain poorly understood. In this study, a fiber-specific promoter proSCFP was applied to drive the expression of GhOR1Del, a positive regulator of carotenoid accumulation, to upregulate the carotenoid level in cotton fiber in planta. Fiber length, strength, and fineness were increased in proSCFP:GhOR1Del transgenic cotton and abscisic acid (ABA) and ethylene contents were increased in elongating fibers. The ABA downstream regulator GhbZIP27a stimulated the expression of the ethylene synthase gene GhACO3 by binding to its promoter, suggesting that ABA promoted fiber elongation by increasing ethylene production. These findings suggest the involvement of carotenoids and ABA signaling in promoting cotton fiber elongation and provide a strategy for improving cotton fiber quality."
Authors: Havza Imtiaz, Yamshi Arif, Pravej Alam and Shamsul Hayat.
Environmental and Experimental Botany (2023)
Highlights: • Apocarotenoids are generated from carotenoids by CCDs and ROS. • CCDs cleave carotenoids at different positions. • Apocarotenoids involved in plant tolerance against abiotic and biotic stresses. • Apocarotenoids modulate the level of phytohormones. • Apocarotenoids are of high economic value in the flavoring and cosmetic industries.
Abstract: "Apocarotenoids are essential metabolites found in all photosynthetic and heterotrophic organisms. Apocarotenoids include phytohormones, signaling molecules, pigments, volatiles, and many other molecules used in flavor, aroma, food, and cosmetics. Apocarotenoids are a crucial component of horticulture crops' quality and contribute to increasing their health benefits. Apocarotenoids are derived from the oxidative breakdown of carotenoids; the reaction can be enzymatic by CCDs and non-enzymatic (non-site specific) by ROS or enzymatic (site specific) by lipoxygenases and peroxidases. The enzymes belong to the family of carotenoid cleavage dioxygenase (CCDs) that includes nine different types of CCDs along with recently identified CCD10, and each plays a decisive role in catalyzing different apocarotenoids. Recent and novel apocarotenoids like β-cyclocitral, anchorene, zaxinone, and ionone were discussed. In all taxa, apocarotenoids perform crucial biological functions. They have a significant role in controlling plants' growth, development, and reaction to biotic and abiotic environmental stimuli and mediating interactions between plants and other lifeforms. This review covers biosynthesis, isolation, characterization, and types of apocarotenoids. It also discusses the regulation of biosynthesis and CCDs genes at different levels, such as transcription (TFs, promoter, and post-transcription), post-translation, and epigenetic modifications. This review limelights the crucial role of apocarotenoids in defense against abiotic and biotic stresses. The crosstalk of apocarotenoids (SLs and ABA) with other phytohormones is also discussed."
Authors: Ming Zeng, Nicole M. van Dam and Bettina Hause.
Physiologia Plantarum (2023)
Abstract: "Ethylene (ET) controls many facets of plant growth and development under abiotic and biotic stresses. MtEIN2, as a critical element of the ET signalling pathway, is essential in biotic interactions. However, the role of MtEIN2 in responding to abiotic stress, such as combined nutrient deficiency, is less known. To assess the role of ethylene signalling in nutrient uptake, we manipulated nitrate (NO3-) and phosphate (Pi) availability for wild type (WT) and the ethylene-insensitive (MtEIN2-defective) mutant, sickle, in Medicago truncatula. We measured leaf biomass and photosynthetic pigments in WT and sickle to identify conditions leading to different responses in both genotypes. Under combined NO3- and Pi deficiency, sickle plants had higher chlorophyll and carotenoid contents than WT plants. Under these conditions, nitrate content and gene expression levels of nitrate transporters were higher in the sickle mutant than in the WT. This led to the conclusion that MtEIN2 is associated with nitrate uptake and the content of photosynthetic pigments under combined Pi and NO3-deficiency in M. truncatula. We conclude that ethylene perception plays a critical role in regulating the nutrient status of plants."
Via Jean-Michel Ané
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