Search

MYB transcription factors (TFs) have been reported to regulate the biosynthesis of secondary metabolites, as well as to mediate plant adaption to abiotic stresses, including drought. However, the roles of MYB TFs in regulating plant architecture and yield potential remain poorly understood. Here, we studied the roles of the dehydration-inducible GmMYB14 gene in regulating plant architecture, high-density yield and drought tolerance through the brassinosteroid (BR) pathway in soybean. GmMYB14 was shown to localize to nucleus and has a transactivation activity. Stable GmMYB14-overexpressing (GmMYB14-OX) transgenic soybean plants displayed a semi-dwarfism and compact plant architecture associated with decreased cell size, resulting in a decrease in plant height, internode length, leaf area, leaf petiole length and leaf petiole angle, and improved yield in high density under field conditions. Results of the transcriptome sequencing suggested the involvement of BRs in regulating GmMYB14-OX plant architecture. Indeed, GmMYB14-OX plants showed reduced endogenous BR contents, while exogenous application of brassinolide could partly rescue the phenotype of GmMYB14-OX plants. Furthermore, GmMYB14 was shown to directly bind to the promoter of GmBEN1 and up-regulate its expression, leading to reduced BR content in GmMYB14-OX plants. GmMYB14-OX plants also displayed improved drought tolerance under field conditions. GmBEN1 expression was also up-regulated in the leaves of GmMYB14-OX plants under polyethylene glycol treatment, indicating that the GmBEN1-mediated reduction in BR level under stress also contributed to drought/osmotic stress tolerance of the transgenic plants. Our findings provided a strategy for stably increasing high-density yield and drought tolerance in soybean using a single TF-encoding gene., (© 2020 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)

Cystathionine-β-synthase (CBS) domain-containing proteins (CDCPs) constitute a large family in plants, and members of this family have been implicated in a variety of biological processes. However, the precise functions and the underlying mechanisms of most members of this family in plants remain to be elucidated. CBSDUF proteins belong to the CDCP superfamily, which contains one domain of unknown function (DUF21) and an N terminus that is adjacent to two intracellular CBS domains. In this study, a comprehensive genome database analysis of soybean was performed to investigate the role(s) of these CBSDUFs and to explore their nomenclature, classification, chromosomal distribution, exon-intron organization, protein structure, and phylogenetic relationships; the analysis identified a total of 18 putative CBSDUF genes. Using specific protein domains and phylogenetic analysis, the CBSDUF gene family was subdivided into eight groups. The soybean CBSDUF genes showed an uneven distribution on 12 chromosomes of Glycine max. RNA-seq transcriptome data from different tissues in public databases revealed tissue-specific and differential expression profiles of the GmCBSDUFs, and qPCR analysis revealed that certain groups of soybean CBSDUFs are likely involved in specific stress responses. In addition, GmCBSDUF3 transgenic Arabidopsis was subjected to phenotypic analysis under NaCl, PEG, and ABA stress treatments. The overexpression of GmCBSDUF3 could enhance tolerance to drought and salt stress in Arabidopsis. This study presents a first comprehensive look at soybean CBSDUF proteins and provides valuable resources for functionally elucidating this protein subgroup within the CBS domain-containing protein family.

Background: Plant papain-like cysteine proteases (PLCPs) are a large class of proteolytic enzymes and play important roles in root nodule symbiosis (RNS), while the whole-genome studies of PLCP family genes in legume are quite limited, and the roles of Glycine max PLCPs (GmPLCPs) in nodulation, nodule development and senescence are not fully understood., Results: In the present study, we identified 97 GmPLCPs and performed a genome-wide survey to explore the expansion of soybean PLCP family genes and their relationships to RNS. Nineteen paralogous pairs of genomic segments, consisting of 77 GmPLCPs, formed by whole-genome duplication (WGD) events were identified, showing a high degree of complexity in duplication. Phylogenetic analysis among different species showed that the lineage differentiation of GmPLCPs occurred after family expansion, and large tandem repeat segment were specifically in soybean. The expression patterns of GmPLCPs in symbiosis-related tissues and nodules identified RNS-related GmPLCPs and provided insights into their putative symbiotic functions in soybean. The symbiotic function analyses showed that a RNS-related GmPLCP gene (Glyma.04G190700) really participate in nodulation and nodule development., Conclusions: Our findings improved our understanding of the functional diversity of legume PLCP family genes, and provided insights into the putative roles of the legume PLCPs in nodulation, nodule development and senescence.

Key Message: Drought tolerance level of 136 soybean genotypes, the correlations among traits were evaluated, and several important drought-tolerant genotypes, traits, SNPs and genes were possibly useful for soybean genetic breeding. Drought is an adverse environmental factor affecting crops growth, development, and yield. Promising genotypes and genes with improved tolerance to drought are probably effective ways to alleviate the situation. In this study, our main task was to determine drought tolerance level of 136 soybean genotypes, the correlations among physiological and agronomic traits under drought, and drought-tolerant single nucleotide polymorphism (SNPs) and genes. In this study, twenty-six varieties were identified as excellent tolerant genotypes to stress among which S14, S93 and S135 with high drought-tolerant index (DTI > 1.3) and yield (Y > 300 kg). Fourteen varieties were identified as drought-sensitive genotypes, such as S25, S45 and S58, with low drought-tolerant index (DTI < 0.5). 422 SNPs and 302 genes correlated with seed number per plant (SNPP), maturity (M), number of seeds per pod (NSPP), node number of main stem (NNMS), Stem diameter (SD) and pull stem (PS) were detected under well-watered and drought conditions by genome-wide association study (GWAS). Among them, we found SNPs (Chr 3:1758920-1958934) between drought-tolerant and sensitive genotypes. 13 genes (Glyma.03G017800, Glyma.03G018000, Glyma.03G018200, Glyma.03G018400, Glyma.03G018500, Glyma.03G018600, Glyma.03G018700, Glyma.03G018800, Glyma.03G018900, Glyma.03G019000, Glyma.03G019100, Glyma.03G019200, Glyma.03G019300) correlated with NNMS were detected. By qRT-PCR, the expression level of Glyma.03G018000 and Glyma.03G018900 in drought-tolerant varieties was significantly increased, but low or no expression in sensitive varieties under drought stress. This study provides important drought-tolerant genotypes, traits, SNPs and potential genes, possibly useful for soybean genetic breeding.

Background: The plant architecture has significant effects on grain yield of various crops, including soybean (Glycine max), but the knowledge on optimization of plant architecture in order to increase yield potential is still limited. Recently, CRISPR/Cas9 system has revolutionized genome editing, and has been widely utilized to edit the genomes of a diverse range of crop plants., Results: In the present study, we employed the CRISPR/Cas9 system to mutate four genes encoding SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors of the SPL9 family in soybean. These four GmSPL9 genes are negatively regulated by GmmiR156b, a target for the improvement of soybean plant architecture and yields. The soybean Williams 82 was transformed with the binary CRISPR/Cas9 plasmid, assembled with four sgRNA expression cassettes driven by the Arabidopsis thaliana U3 or U6 promoter, targeting different sites of these four SPL9 genes via Agrobacterium tumefaciens-mediated transformation. A 1-bp deletion was detected in one target site of the GmSPL9a and one target site of the GmSPL9b, respectively, by DNA sequencing analysis of two T0-generation plants. T2-generation spl9a and spl9b homozygous single mutants exhibited no obvious phenotype changes; but the T2 double homozygous mutant spl9a/spl9b possessed shorter plastochron length. In T4 generation, higher-order mutant plants carrying various combinations of mutations showed increased node number on the main stem and branch number, consequently increased total node number per plants at different levels. In addition, the expression levels of the examined GmSPL9 genes were higher in the spl9b-1 single mutant than wild-type plants, which might suggest a feedback regulation on the expression of the investigated GmSPL9 genes in soybean., Conclusions: Our results showed that CRISPR/Cas9-mediated targeted mutagenesis of four GmSPL9 genes in different combinations altered plant architecture in soybean. The findings demonstrated that GmSPL9a, GmSPL9b, GmSPL9c and GmSPL9 function as redundant transcription factors in regulating plant architecture in soybean.

Nitrogen is an important macronutrient required for plant growth, and is a limiting factor for crop productivity. Improving the nitrogen use efficiency (NUE) is therefore crucial. At present, the NUE mechanism is unclear and information on the genes associated with NUE in soybeans is lacking. cystathionine beta synthase (CBS) domain-containing proteins (CDCPs) may be implicated in abiotic stress tolerance in plants. We identified and classified a CBS domain-containing protein superfamily in soybean. A candidate gene for NUE, GmCBS21, was identified. GmCBS21 gene characteristics, the temporal expression pattern of the GmCBS21 gene, and the phenotype of GmCBS21 overexpression in transgenic Arabidopsis thaliana under low nitrogen stress were analyzed. The phenotypes suggested that the transgenic Arabidopsis thaliana seedlings performed better under the nitrogen-deficient condition. GmCBS21-overexpressing transgenic plants exhibit higher low nitrogen stress tolerance than WT plants, and this suggests its role in low nitrogen stress tolerance in plants. We conclude that GmCBS21 may serve as an excellent candidate for breeding crops with enhanced NUE and better yield.

GATA transcription factors are transcriptional regulatory proteins that contain a characteristic type-IV zinc finger DNA-binding domain and recognize the conserved GATA motif in the promoter sequence of target genes. Previous studies demonstrated that plant GATA factors possess critical functions in developmental control and responses to the environment. To date, the GATA factors in soybean (Glycine max) have yet to be characterized. Thus, this study identified 64 putative GATA factors from the entire soybean genomic sequence. The chromosomal distributions, gene structures, duplication patterns, phylogenetic tree, tissue expression patterns, and response to low nitrogen stress of the 64 GATA factors in soybean were analyzed to further investigate the functions of these factors. Results indicated that segmental duplication predominantly contributed to the expansion of the GATA factor gene family in soybean. These GATA proteins were phylogenetically clustered into four distinct subfamilies, wherein their gene structure and motif compositions were considerably conserved. A comparative phylogenetic analysis of the GATA factor zinc finger domain sequences in soybean, Arabidopsis (Arabidopsis thaliana), and rice (Oryza sativa) revealed four major classes. The GATA factors in soybean exhibited expression diversity among different tissues; some of these factors showed tissue-specific expression patterns. Numerous GATA factors displayed upregulation or downregulation in soybean leaf in response to low nitrogen stress, and two GATA factors GATA44 and GATA58 were likely to be involved in the regulation of nitrogen metabolism in soybean. Overexpression of GmGATA44 complemented the reduced chlorophyll phenotype of the Arabidopsis ortholog AtGATA21 mutant, implying that GmGATA44 played an important role in modulating chlorophyll biosynthesis. Overall, our study provides useful information for the further analysis of the biological functions of GATA factors in soybean and other crops.

The macronutrient potassium (K) is essential to plant growth and development. Crop yield potential is often affected by lack of soluble K. The molecular regulation mechanism of physiological and biochemical responses to K starvation in soybean roots and shoots is not fully understood. In the present study, two soybean varieties were subjected to low-K stress conditions: a low-K-tolerant variety (You06-71) and a low-K-sensitive variety (HengChun04-11). Eight libraries were generated for analysis: 2 genotypes ×2 tissues (roots and shoots) ×2 time periods [short term (0.5 to 12 h) and long term (3 to 12 d)]. RNA derived from the roots and shoots of these two varieties across two periods (short term and long term) were sequenced and the transcriptomes were compared using high-throughput tag-sequencing. To this end, a large number of clean tags (tags used for analysis after removal of dirty tags) corresponding to distinct tags (all types of clean tags) were identified in eight libraries (L1, You06-71-root short term; L2, HengChun04-11-root short term; L3, You06-71-shoot short term; L4, HengChun04-11-shoot short term; L5, You06-71-root long term; L6, HengChun04-11-root long term; L7, You06-71-shoot long term; L8, HengChun04-11-shoot long term). All clean tags were mapped to the available soybean (Glycine max) transcript database (http://www.soybase.org). Many genes showed substantial differences in expression across the libraries. In total, 5,440 transcripts involved in 118 KEGG pathways were either up- or down-regulated. Fifteen genes were randomly selected and their expression levels were confirmed using quantitative RT-PCR. Our results provide preliminary information on the molecular mechanism of potassium absorption and transport under low-K stress conditions in different soybean tissues.

Chlorophyll plays an essential role in photosynthetic light harvesting and energy transduction in green tissues of higher plants and is closely related to photosynthesis and crop yield. Identification of transcription factors (TFs) involved in regulating chlorophyll biosynthesis is still limited in soybean (Glycine max), and the previously identified GmGATA58 is suggested to potentially modulate chlorophyll and nitrogen metabolisms, but its complete function is still unknown. In this study, subcellular localization assay showed that GmGATA58 was localized in the nucleus. Histochemical GUS assay and qPCR assay indicated that GmGATA58 was mainly expressed in leaves and responded to nitrogen, light and phytohormone treatments. Overexpression of GmGATA58 in the Arabidopsis thaliana ortholog AtGATA21 (gnc) mutant complemented the greening defect, while overexpression in Arabidopsis wild-type led to increasing chlorophyll content in leaves through up-regulating the expression levels of the large of chlorophyll biosynthetic pathway genes, but suppressing plant growth and yield, although the net photosynthetic rate was slightly improved. Dual-luciferase reporter assay also supported that GmGATA58 activated the transcription activities of three promoters of key chlorophyll biosynthetic genes of soybean in transformed protoplast of Arabidopsis. It is concluded that GmGATA58 played an important role in regulating chlorophyll biosynthesis, but suppressed plant growth and yield in transgenic Arabidopsis. [ABSTRACT FROM AUTHOR]