Chen L, Yang H, Fang Y, Guo W, Chen H, Zhang X, Dai W, Chen S, Hao Q, Yuan S, Zhang C, Huang Y, Shan Z, Yang Z, Qiu D, Liu X, Tran LP, Zhou X, Cao D.

Plant Biotechnol J. 2021 Apr; 19(4):702-716.

Abstract

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.

See: https://pubmed.ncbi.nlm.nih.gov/33098207/

Figure 7: GmMYB14 directly activates the expression of GmBEN1 gene. (a) Schematic diagram of the GmBEN1 promoter with four putative AC elements ‘ACC(A/T)A(A/C)C’ within 1‐kb region upstream of the ATG. (b) Electrophoretic mobility shift assay (EMSA) indicates that the GmMYB14 binds to the first putative AC element ‘ACCTACC’ of the GmBEN1 promoter shown in (a). The 30‐bp fragment containing the first AC element was used as a hot probe in the EMSA. Binding competition was tested using the 100× competitive cold probe. Biotin probe was used as negative control. (c) Yeast one‐hybrid assay indicated the binding of GmMYB14 to the 31‐bp sequence of the GmBEN1 promoter. Yeast cells from serial dilutions (1:10, 1:100 and 1:1000) were grown on SD/‐Leu/‐Ura medium supplemented with different concentrations of aureobasidin A (AbA). The empty pGADT7 vector was used as negative control. (d) GmMYB14 protein promotes the transcription of LUC (LUCIFERASE) reporter gene driven by the 1‐kb pGmBEN1 promoter inArabidopsisprotoplasts. LUC activities were normalized to the respective Renilla luciferase (REN) activity and were expressed in relative expression units. Data shown are means and standard deviations of three replicates (n = 3), with asterisks showing statistically significant difference (**P < 0.01; Student's t‐test). (e–f) Contents of endogenous brassinosteroids, including (e) castasterone (CS) and (f) 6‐deoxo‐castasterone (6‐deoxo‐CS), in the shoots of 2‐week‐old OX9 transgenic and wild‐type (WT) plants. Data shown are means and standard deviations of three replicates (n = 3), with asterisks showing statistically significant differences (**P < 0.01; Student's t‐test). (g‐h) Phenotypes of 17‐day‐old WT plants, T3‐generation OX9 (g) and OX12 (h) after spaying with 0, 1, 5 or 10 μM brassinolide (BL). (i–l) Plant height, leaf area, leaf petiole angle and leaf petiole length of the OX9, OX12 and WT plants shown in (g–h). Data shown are means and standard deviations (n = 18 plants/genotype/treatment). Significant differences were shown by different letters following Duncan’s multiple‐range test (P < 0.05).