Soybean GmWRKY44 transcription factor activates SOC1 and LFY to promote flowering in Arabidopsis thaliana.

Key message: Soybean GmWRKY44 can directly activate the expressions of SOC1 and LFY to promote flowering in Arabidopsis. WRKY transcription factors (TFs) play pivotal roles in regulating plant flowering; however, the molecular mechanism underlying flowering regulation by soybean (Glycine max) WRKY TFs remains elusive. In this study, we isolated GmWRKY44, a nuclear-localized Group IIc WRKY member exhibiting transcriptional activation capacity. GmWRKY44 displayed spatiotemporal specificity, with peak expression in 30 d post-germination stems. GUS staining showed that GmWRKY44 expressed in various tissues, such as roots, stems, leaves, sepals, stigmas, filaments, siliques and seedlings. GmWRKY44 promoter harbored 92 cis-elements associated with phytohormone responses, light signaling, abiotic stress adaptation and developmental regulation. Furthermore, the overexpression of GmWRKY44 in Arabidopsis led to an early-flowering phenotype, as evidenced by the significant upregulation of flowering activators SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), LEAFY (LFY), APETALA1 (AP1) and downregulation of the flowering repressor FLOWERING LOCUS C (FLC). Subsequent analyses, including Y1H, EMSA, and LUC assays, provided convincing evidences that GmWRKY44 directly bound to the promoters of SOC1 and LFY, thereby elevating their expression. Genetic complementation assays further revealed that OE44-1 soc1-2 and OE44-1 lfy-2 hybrids exhibited a later flowering time than OE44-1 plants, indicating that the loss of SOC1 or LFY genetically arrested the early-flowering of OE44-1. In summary, this study revealed that GmWRKY44 promoted flowering in Arabidopsis by directly upregulating SOC1 and LFY, thus addressing a critical knowledge gap in the molecular regulation of soybean WRKYs on flowering time and offering a novel candidate gene for optimizing flowering time to enhance soybean yield across diverse agroecological zones.