Soybean GmMYB73 promotes lipid accumulation in transgenic plants.

BACKGROUND: Soybean is one of the most important oil crops. The regulatory genes involved in oil accumulation are largely unclear. We initiated studies to identify genes that regulate this process. RESULTS: One MYB-type gene GmMYB73 was found to display differential expression in soybean seeds of different developing stages by microarray analysis and was further investigated for its functions in lipid accumulation. GmMYB73 is a small protein with single MYB repeat and has similarity to CPC-like MYB proteins from Arabidopsis. GmMYB73 interacted with GL3 and EGL3, and then suppressed GL2, a negative regulator of oil accumulation. GmMYB73 overexpression enhanced lipid contents in both seeds and leaves of transgenic Arabidopsis plants. Seed length and thousand-seed weight were also promoted. GmMYB73 introduction into the Arabidopsis try cpc double mutant rescued the total lipids, seed size and thousand-seed weight. GmMYB73 also elevated lipid levels in seeds and leaves of transgenic Lotus, and in transgenic hairy roots of soybean plants. GmMYB73 promoted PLDα1 expression, whose promoter can be bound and inhibited by GL2. PLDα1 mutation reduced triacylglycerol levels mildly in seeds but significantly in leaves of Arabidopsis plants. CONCLUSIONS: GmMYB73 may reduce GL2, and then release GL2-inhibited PLDα1 expression for lipid accumulation. Manipulation of GmMYB73 may potentially improve oil production in legume crop plants.

Soybean GmbZIP123 gene enhances lipid content in the seeds of transgenic Arabidopsis plants.

Soybean is one of most important oil crops and a significant increase in lipid content in soybean seeds would facilitate vegetable oil production in the world. Although the pathways for lipid biosynthesis in higher plants have been uncovered, our understanding of regulatory mechanism controlling lipid accumulation is still limited. In this study, we identified 87 transcription factor genes with a higher abundance at the stage of lipid accumulation in soybean seeds. One of these genes, GmbZIP123, was selected to further study its function in regulation of lipid accumulation. Overexpression of GmbZIP123 enhanced lipid content in the seeds of transgenic Arabidopsis thaliana plants. The GmbZIP123 transgene promoted expression of two sucrose transporter genes (SUC1 and SUC5) and three cell-wall invertase genes (cwINV1, cwINV3, and cwINV6) by binding directly to the promoters of these genes. Consistently, the cell-wall invertase activity and sugar translocation were all enhanced in siliques of GmbZIP123 transgenic plants. Higher levels of glucose, fructose, and sucrose were also found in seeds of GmbZIP123 transgenic plants. These results suggest that GmbZIP123 may participate in regulation of lipid accumulation in soybean seeds by controlling sugar transport into seeds from photoautotrophic tissues. This study provides novel insights into the regulatory mechanism for lipid accumulation in seeds and may facilitate improvements in oil production in soybean and other oil crops through genetic manipulation of the GmbZIP123 gene.

A PP2C-1 Allele Underlying a Quantitative Trait Locus Enhances Soybean 100-Seed Weight.

Cultivated soybeans may lose some useful genetic loci during domestication. Introgression of genes from wild soybeans could broaden the genetic background and improve soybean agronomic traits. In this study, through whole-genome sequencing of a recombinant inbred line population derived from a cross between a wild soybean ZYD7 and a cultivated soybean HN44, and mapping of quantitative trait loci for seed weight, we discovered that a phosphatase 2C-1 (PP2C-1) allele from wild soybean ZYD7 contributes to the increase in seed weight/size. PP2C-1 may achieve this function by enhancing cell size of integument and activating a subset of seed trait-related genes. We found that PP2C-1 is associated with GmBZR1, a soybean ortholog of Arabidopsis BZR1, one of key transcription factors in brassinosteroid (BR) signaling, and facilitate accumulation of dephosphorylated GmBZR1. In contrast, the PP2C-2 allele with variations of a few amino acids at the N-terminus did not exhibit this function. Moreover, we showed that GmBZR1 could promote seed weight/size in transgenic plants. Through analysis of cultivated soybean accessions, we found that 40% of the examined accessions do not have the PP2C-1 allele, suggesting that these accessions can be improved by introduction of this allele. Taken together, our study identifies an elite allele PP2C-1, which can enhance seed weight and/or size in soybean, and pinpoints that manipulation of this allele by molecular-assisted breeding may increase production in soybean and other legumes/crops.