A R2R3-MYB Transcription Factor of GmMYB62 Regulates Seed-Coat Color and Seed Size in Arabidopsis

The seed-coat color and seed size have an impact on both the evolutionary fitness and the grain yield of crops. Soybean is a major oil crop, and the seed-coat color and seed size exhibit natural diversity among the different soybean varieties. Here, we found an R2R3-MYB transcription factor of <i>GmMYB62</i>, which shows a significant increase in expression as the seed-coat color changes from yellow to black in different soybean varieties. The <i>GmMYB62</i> was specifically highly expressed in reproductive organs, especially in floral organs in soybeans. The <i>GmMYB62</i> encodes a nuclear protein that contains two MYB domains. In the phylogenetic analysis, the GmMYB62 was relatively conserved after the divergence of the monocots and dicots, and it also grouped with transcriptional repressors of MYBs in anthocyanin synthesis. The <i>GmMYB62</i> was overexpressed in Arabidopsis and the seeds displayed a pale-brown coat in <i>GmMYB62</i> overexpression lines, in contrast to the dark-brown seed coat observed in wild-type of Col-0. The anthocyanin content in the <i>GmMYB62</i> overexpression lines was dramatically reduced when compared to Col-0. Additionally, the seeds in overexpression lines showed shorter lengths, larger widths, and lower thousand-seed weights than those in Col-0. Furthermore, the genes related to anthocyanin synthesis and seed size regulation were investigated, and expression of eight genes that involved in anthocyanin synthesis pathway, like <i>chalcone synthase</i> (<i>CHS</i>), <i>chalcone isomerase</i> (<i>CHI</i>), <i>flavanone 3-hydroxylase</i> (<i>F3H</i>), and <i>anthocyanidin synthase</i> (<i>ANS</i>) were severely inhibited in the <i>GmMYB62</i> overexpression lines when compared to Col-0. In addition, the <i>ARGOS-LIKE</i> (<i>ARL</i>), <i>B-Type Cyclin 1</i> (<i>CYCB1</i>), and <i>enhancer of DA1-1</i> (<i>EOD3</i>), which govern cell expansion and proliferation, were highly expressed in <i>GmMYB62</i> overexpression lines when compared to Col-0. Overall, this study sheds new light on the control of seed-coat color and seed size by <i>GmMYB62</i> and provides potentially valuable targets for improving crop seed quality.