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Authors: Xing Wang, Zhaobin Ren, Shipeng Xie, Zhaohu Li, Yuyi Zhou and Liusheng Duan.
Plant Physiology (2024)
One-sentence summary: A jasmonate mimic regulates a basic helix-loop-helix network by attenuating brassinosteroid signaling, which represses expression of a cell wall–related gene and inhibits internode elongation in maize.
Abstract: "Lodging restricts growth, development, and yield formation in maize (Zea mays L.). Shorter internode length is beneficial for lodging tolerance. However, although brassinosteroids (BRs) and jasmonic acid (JA) are known to antagonistically regulate internode growth, the underlying molecular mechanism is still unclear. In this study, application of the JA mimic coronatine (COR) inhibited basal internode elongation at the jointing stage and repressed expression of the cell wall-related gene XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDROLASE 1 (ZmXTH1), whose overexpression in maize plants promotes internode elongation. We demonstrated that the basic helix–loop–helix (bHLH) transcription factor ZmbHLH154 binds directly to the ZmXTH1 promoter and induces its expression, whereas the bHLH transcription factor ILI1 BINDING BHLH 1 (ZmIBH1) inhibits this transcriptional activation by forming a heterodimer with ZmbHLH154. Overexpressing ZmbHLH154 led to longer internodes, whereas zmbhlh154 mutants had shorter internodes than the wild type. The core JA-dependent transcription factors ZmMYC2-4 and ZmMYC2-6 interacted with BRASSINAZOLE RESISTANT 1 (ZmBZR1), a key factor in BR signaling, and these interactions eliminated the inhibitory effect of ZmBZR1 on its downstream gene ZmIBH1. Collectively, these results reveal a signaling module in which JA regulates a bHLH network by attenuating BR signaling to inhibit ZmXTH1 expression, thereby regulating cell elongation in maize."
Authors: Fereshteh Jafari, Baobao Wang, Haiyang Wang and Junjie Zou.
Journal of Integrative Plant Biology (2023)
Abstract: "Maize is a major staple crop widely used as food, animal feed, and raw materials in industrial production. High-density planting is a major factor contributing to the continuous increase of maize yield. However, high planting density usually triggers a shade avoidance response and causes increased plant height and ear height, resulting in lodging and yield loss. Reduced plant height and ear height, more erect leaf angle, reduced tassel branch number, earlier flowering, and strong root system architecture are five key morphological traits required for maize adaption to high-density planting. In this review, we summarize recent advances in deciphering the genetic and molecular mechanisms of maize involved in response to high-density planting. We also discuss some strategies for breeding advanced maize cultivars with superior performance under high-density planting conditions."
Authors: Canran Sun, Yang Liu, Guofang Li, Yanle Chen, Mengyuan Li, Ruihua Yang, Yongtian Qin, Yongqiang Chen, Jinpeng Cheng, Jihua Tang and Zhiyuan Fu.
The Crop Journal (2024)
Abstract: "Plant height (PH) is associated with lodging resistance and planting density, which is regulated by a complicated gene network. In this study, we identified a spontaneous dwarfing mutation in maize, m30, with decreased internode number and length but increased internode diameter. A candidate gene, ZmCYP90D1, which encodes a member of the cytochrome P450 family, was isolated by map-based cloning. ZmCYP90D1 was constitutively expressed and showed highest expression in basal internodes, and its protein was targeted to the nucleus. A G-to-A substitution was identified to be the causal mutation, which resulted in a truncated protein in m30. Loss of function of ZmCYP90D1 changed expression of hormone-responsive genes, in particular brassinosteroid (BR)-responsive genes which is mainly involved in cell cycle regulation and cell wall extension and modification in plants. The concentration of typhasterol (TY), a downstream intermediate of ZmCYP90D1 in the BR pathway, was reduced. A haplotype conferring dwarfing without reducing yield was identified. ZmCYP90D1 was inferred to influence plant height and stalk diameter via hormone-mediated cell division and cell growth via the BR pathway."
Authors: Shizhan Chen, Xiaocong Fan, Meifang Song, Shuaitao Yao, Tong Liu, Wusi Ding, Lei Liu, Menglan Zhang, Weimin Zhan, Lei Yan, Guanghua Sun, Hongdan Li, Lijian Wang, Kang Zhang, Xiaolin Jia, Qinghua Yang and Jianping Yang.
Plant Physiology (2023)
Abstract: "Maize (Zea mays L.) is one of the most important crops worldwide. Photoperiod, light quality, and light intensity in the environment can affect the growth, development, yield, and quality of maize. In Arabidopsis (Arabidopsis thaliana), cryptochromes are blue-light receptors that mediate the photocontrol of stem elongation, leaf expansion, shade tolerance, and photoperiodic flowering. However, the function of maize cryptochrome ZmCRY in maize architecture and photomorphogenic development remains largely elusive. The ZmCRY1b transgene product can activate the light signaling pathway in Arabidopsis and complement the etiolation phenotype of the cry1-304 mutant. Our findings show that the loss-of-function mutant of ZmCRY1b in maize exhibits more etiolation phenotypes under low blue light and appears slender in the field compared with wild-type plants. Under blue and white light, overexpression of ZmCRY1b in maize substantially inhibits seedling etiolation and shade response by enhancing protein accumulation of the bZIP transcription factors ELONGATED HYPOCOTYL 5 (ZmHY5) and ELONGATED HYPOCOTYL 5-LIKE (ZmHY5L), which directly upregulate the expression of genes encoding gibberellin (GA) 2-oxidase to deactivate GA and repress plant height. More interestingly, ZmCRY1b enhances lodging resistance by reducing plant and ear heights and promoting root growth in both inbred lines and hybrids. In conclusion, ZmCRY1b contributes blue-light signaling upon seedling de-etiolation and integrates light signals with the GA metabolic pathway in maize, resulting in lodging resistance and providing information for improving maize varieties."
Authors: Jiao Shu-liang, Li Qin-yan, Zhang Fan, Tao Yong-hong, Yu Ying-zhen, Yao Fan, Li Qing-mao, Hu Feng-yi and Huang Li-yu.
Journal of Integrative Agriculture (2024)
Abstract: "Semidwarf breeding has boosted crop production and is a well-known outcome from the first Green Revolution. The Green Revolution gene Semidwarf 1 (SD1), which modulates gibberellic acid (GA) biosynthesis, plays a principal role in rice plant height. Mutation in SD1 reduces rice plant height and promotes lodging resistance and fertilizer tolerance to increase grain production. Plant height mediated by SD1 also favours grain yield under certain conditions. However, it is not yet known whether the function of SD1 in upland rice promotes adaptation and grain production. In this study, the plant height and grain yield of irrigated and upland rice were comparatively analysed under paddy and dryland conditions. In response to dryland environments, rice requires a reduction in plant height to cope with water deficits. Upland rice accessions had greater plant height than their irrigated counterparts under both paddy and dryland conditions, and appropriately reducing plant height could promote adaptability to dryland environments and maintain high grain yield formation. Moreover, upland rice cultivars with thicker stem diameters had stronger lodging resistance, which addresses the lodging problem. Knockout of SD1 in the upland rice cultivar IRAT104 reduced the plant height and grain yield, demonstrating that adjustment of the plant height mediated by SD1 could increase grain production in dryland fields. In addition, SD1 genetic diversity analysis verified that haplotype variation caused phenotypic variation in plant height. During the breeding history of rice, SD1 allelic mutations were selected from landraces to improve the grain yield of irrigated rice cultivars, and this selection was accompanied by reduced plant height. Thus, five known mutant alleles were analysed to verify that functional SD1 is required for upland rice production. All these results suggest that SD1 might undergo artificial positive selection in upland rice, which provides further insights concerning greater plant height in upland rice breeding.
Authors: Getu Beyene, Raj Deepika Chauhan, Justin Villmer, Nada Husic, Ning Wang, Endale Gebre, Dejene Girma, Solomon Chanyalew, Kebebew Assefa, Girma Tabor, Malia Gehan, Michael McGrone, Meizhu Yang, Brian Lenderts, Chris Schwartz, Huirong Gao, William Gordon-Kamm, Nigel J. Taylor and Donald J. MacKenzie.
Plant Biotechnology Journal (2022)
Abstract: "Tef is a staple food and a valuable cash crop for millions of people in Ethiopia. Lodging is a major limitation to tef production, and for decades, the development of lodging resistant varieties proved difficult with conventional breeding approaches. We used CRISPR/Cas9 to introduce knockout mutations in the tef orthologue of the rice SEMIDWARF-1 (SD-1) gene to confer semidwarfism and ultimately lodging resistance. High frequency recovery of transgenic and SD-1 edited tef lines was achieved in two tef cultivars by Agrobacterium-mediated delivery into young leaf explants of gene editing reagents along with transformation and regeneration enhancing morphogenic genes, BABY BOOM (BBM) and WUSCHEL2 (WUS2). All of the 23 lines analyzed by next-generation sequencing had at least two or more alleles of SD-1 mutated. Of these, 83% had tetra-allelic frameshift mutations in the SD-1 gene in primary tef regenerants, which were inherited in subsequent generations. Phenotypic data generated on T1 and T2 generations revealed that the sd-1 lines have reduced culm and internode lengths with no reduction in either panicle or peduncle lengths. These characteristics are comparable with rice sd-1 plants. Measurements of lodging, in greenhouse-grown plants, showed that sd-1 lines have significantly higher resistance to lodging at the heading stage compared with the controls. This is the first demonstration of the feasibility of high frequency genetic transformation and CRISPR/Cas9-mediated genome editing in this highly valuable but neglected crop. The findings reported here highlight the potential of genome editing for the improvement of lodging resistance and other important traits in tef."
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Authors: Barbora Ndreca, Alison Huttly, Sajida Bibi, Carlos Bayon, George Lund, Joshua Ham, Rocío Alarcón-Reverte, John Addy, Danuše Tarkowská, Stephen Pearce, Peter Hedden, Stephen G. Thomas and Andrew L. Phillips.
Research Square (2024)
Abstract: "Background - Semi-dwarfing alleles are used widely in cereals to confer improved lodging resistance and assimilate partitioning. The most widely deployed semi-dwarfing alleles in rice and barley encode the gibberellin (GA)-biosynthetic enzyme GA 20-OXIDASE2 (GA20OX2). The hexaploid wheat genome carries three homoeologous copies of GA20OX2, and because of functional redundancy, loss-of-function alleles of a single homoeologue would not be selected in wheat breeding programmes. Instead, approximately 70% of wheat cultivars carry gain-of-function mutations in REDUCED HEIGHT 1 (RHT1) genes that encode negative growth regulators and are degraded in response to GA. Semi-dwarf Rht-B1b or Rht-D1b alleles encode proteins that are insensitive to GA-mediated degradation. However, because RHT1 is expressed ubiquitously these alleles have pleiotropic effects that confer undesirable traits in some environments. Results - We have applied reverse genetics to combine loss-of-function alleles in all three homoeologues of wheat GA20OX2 and its paralogue GA20OX1 and evaluated their performance in three years of field trials. ga20ox1 mutants exhibited a mild height reduction (approximately 3%) suggesting GA20OX1 plays a minor role in stem elongation in wheat. ga20ox2 mutants have reduced GA1 content and are 12-32% shorter than their wild-type segregants, comparable to the effect of the Rht-D1b ‘Green Revolution’ allele. The ga20ox2 mutants showed no significant negative effects on yield components, although these alleles should be evaluated in different genetic backgrounds and environments. Conclusions - Our study demonstrates that induced mutagenesis can expand genetic variation in polyploid crops to uncover novel alleles and that mutations in GA20OX2 could have utility in wheat breeding as alternative semi-dwarfing alleles.
Authors: Xiujie Liu, Kai Huang and Chengcai Chu.
Plant Communications (2024)
Excerpts: "Very recently, Li et al. (2023) identified an ideal allele for compact plant architecture in soybean, reduced internode 1 (rin1), that downregulates plant height by reducing internode length and increases total yield per plot under dense planting conditions (Figure 1C). Li et al. have screened out a dwarf mutant from the mutant library in the background of Heinong 35 (HN35), an elite soybean cultivar in China. Interestingly, the reduced plant height of the mutant was mainly caused by the shortened internode, and the yield per plant of rin1 is higher than HN35 (Li et al., 2023). With F2 segregating population derived from the cross between rin1 and Heihe 43 (HH43), another elite cultivar, as well as a residual heterozygous inbred population from the F2 segregating population, the candidate gene of rin1 was cloned."
"In summary, the work of Li et al. (2023) that not only provides a potential elite allele, rin1, for soybean GR, but also uncovers the molecular mechanism of plant height and internode length regulation by RIN1, making a groundbreaking advance in soybean breeding for dense planting to enhance grain yield. Introducing rin1 into more elite soybean cultivars would be an effective strategy to promote the leap of soybean production, especially for China, which has a substantially lower soybean yield compared to USA, which has benefited from soybean varieties with enhanced lodging resistance to adapt to high-density planting (Figure 1B)."
Authors: Shichen Li, Zhihui Sun, Qing Sang, Chao Qin, Lingping Kong, Xin Huang, Huan Liu, Tong Su, Haiyang Li, Milan He, Chao Fang, Lingshuang Wang, Shuangrong Liu, Bin Liu, Baohui Liu, Xiangdong Fu, Fanjiang Kong and Sijia Lu
Nature Communications (2023)
Editor's view: Many cereal crops have been bred to be more compact to allow high-density planting, but soybean has remained relatively overlooked. Here, the authors describe a compact soybean mutant, reduced internode 1, that significantly enhances grain yield under high-density planting conditions compared to an elite cultivar.
Abstract: "Major cereal crops have benefitted from Green Revolution traits such as shorter and more compact plants that permit high-density planting, but soybean has remained relatively overlooked. To balance ideal soybean yield with plant height under dense planting, shortening of internodes without reducing the number of nodes and pods is desired. Here, we characterized a short-internode soybean mutant, reduced internode 1 (rin1). Partial loss of SUPPRESSOR OF PHYA 105 3a (SPA3a) underlies rin1. RIN1 physically interacts with two homologs of ELONGATED HYPOCOTYL 5 (HY5), STF1 and STF2, to promote their degradation. RIN1 regulates gibberellin metabolism to control internode development through a STF1/STF2–GA2ox7 regulatory module. In field trials, rin1 significantly enhances grain yield under high-density planting conditions comparing to its wild type of elite cultivar. rin1 mutants therefore could serve as valuable resources for improving grain yield under high-density cultivation and in soybean–maize intercropping systems. Many cereal crops have been bred to be more compact to allow high-density planting, but soybean has remained relatively overlooked. Here, the authors describe a compact soybean mutant, reduced internode 1, that significantly enhances grain yield under high-density planting conditions compared to an elite cultivar."
Authors: Hao Wu, Beibei Bai, Xiaoduo Lu and Haiyan Li.
Plant Cell Reports (2023)
Key message: The reduction in endogenous gibberellin improved drought resistance, but decreased cellulose and lignin contents, which made the mutant prone to lodging.
Abstract; "It is well known that gibberellin (GA) is a hormone that plays a vital role in plant growth and development. In recent years, a growing number of studies have found that gibberellin plays an important role in regulating the plant height, stem length, and stressed growth surfaces. In this study, a dwarf maize mutant was screened from an EMS-induced mutant library of maize B73. The mutated gene was identified as KS, which encodes an ent-kaurene synthase (KS) enzyme functioning in the early biosynthesis of GA. The mutant was named as ks3-1. A significant decrease in endogenous GA levels was verified in ks3-1. A significantly decreased stem strength of ks3-1, compared with that of wild-type B73, was found. Significant decreases in the cellulose and lignin contents, as well as the number of epidermal cell layers, were further characterized in ks3-1. The expression levels of genes responsible for cellulose and lignin biosynthesis were induced by exogenous GA treatment. Under drought stress conditions, the survival rate of ks3-1 was significantly higher than that of the wild-type B73. The survival rates of both wild-type B73 and ks3-1 decreased significantly after exogenous GA treatment. In conclusion, we summarized that a decreased level of GA in ks3-1 caused a decreased plant height, a decreased stem strength as a result of cell wall defects, and an increased drought tolerance. Our results shed light on the importance of GA and GA-defective mutants in the genetic improvement of maize and breeding maize varieties."
Authors: Hongning Tong and Chengcai Chu.
Journal of Genetics and Genomics (2023)
Excerpts: "The Green Revolution, which took place in the 1960s, was instrumental in increasing grain yields and mitigating the world's food crisis. Breeding semi-dwarfing crops was a critical activity that significantly improved lodging resistance, field management, and harvesting convenience. Subsequent molecular genetic studies revealed that the semi-dwarfing genes used in rice and wheat, two major staple crops, are related to the plant hormone gibberellin (GA)."
"Notably, a recent study by Song et al. (2023) demonstrated that a combination of changes in BR signaling and GA signaling can produce semi-dwarf plant height in wheat, while simultaneously improving NUE (Song et al., 2023). Together with many other superior features, such as compact plant structure, increased grain size, and heavier spike weight, the study's findings offer a novel strategy for simultaneously optimizing multiple traits."
"These traits resulted in a significant yield increase (8.4%-13.8%) for r-e-z wheat, which was more pronounced at high planting densities due to its compact plant architecture, leading to improved population photosynthetic efficiency. Concurrently, the increase in yield was accompanied by improved lodging resistance, as demonstrated in the large-scale field trials."
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