Soybean WRINKLED1 protein GmWRI1a promotes flowering under long-day conditions via regulating expressions of flowering-related genes

Flowering time is an important agronomic character that influences the adaptability and yield of soybean [Glycine max (L.) Merrill]. WRINKLED 1 (WRI1) plays an important regulatory role in plant growth and development. In this study, we found that the expression of GmWIR1a could be induced by long days. Compared with the wild type, transgenic soybean overexpressing GmWRI1a showed earlier flowering and maturity under long days but no significant changes under short days. Overexpression of GmWRI1a led to up-regulated expression of genes involved in the regulation of flowering time. The GmWRI1a protein was able to directly bind to the promoter regions of GmAP1, GmFUL1a, GmFUL2 and up-regulated their expression. GmCOL3 was identified by yeast one-hybrid library screening using the GmWRI1a promoter as bait. GmCOL3 was revealed to be a nucleus-localized protein that represses the transcription of GmWRI1a. Expression of GmCOL3 was induced by short days. Taken together, the results show that overexpression of GmWRI1a promotes flowering under long days by promoting the transcriptional activity of flowering-related genes in soybean, and that GmCOL3 binds to the GmWRI1a promoter and directly down-regulates its transcription. This discovery reveals a new function for GmWRI1a, which regulates flowering and maturity in soybean.