The transcription factor REM16a promotes flowering time in soybean by activating flowering-related genes

The flowering time of soybean [Glycine max (L.) Merr.] is extremely sensitive to photoperiod, which importantly influences its yield potential and restricts the geographical range of soybean cultivars to specific latitudes. Molecular breeding to modulate flowering time and reduce sensitivity to day length is an effective approach to enhance the adaptability and productivity of soybean. Here, we characterized reproductive meristem 16a (GmREM16a), a member of the AP2/B3-like transcription factor family. The GmREM16a protein contains 2 B3 domains, and the expression of its encoding gene is responsive to photoperiod and circadian rhythm. The overexpression of GmREM16a in soybean accelerated flowering by regulating the expression of flowering-related genes. The GmREM16a protein was able to directly bind to the promoters of GmSOC1, GmFT2a, and GmFT5a and upregulate their expression. Yeast two-hybrid screening revealed that GmCSN5 interacts with GmREM16a. GmCSN5 is the fifth subunit of the COP9 signalosome (constitutively photomorphogenic signalosome, CSN) that regulates the activity of CULLIN-RING E3 ubiquitin ligases and regulates protein degradation. Protein degradation assays in vivo and in vitro showed that GmCSN5 promotes the degradation of GmREM16a protein via the ubiquitin-proteasome pathway. Taken together, these findings indicate that the transcription factor GmREM16a promotes flowering by regulating the expression of flowering-related genes. Additionally, GmCSN5 interacts with GmREM16a to regulate its stability in soybean. The GmREM16a-GmSCN5 module may represent a pathway involved in the regulation of flowering time in soybean and is a useful genetic resource for improving the adaptability of soybean through molecular breeding approaches.