The transcription factors GmSTF1 and GmSTF2 promote photosynthesis and lignin biosynthesis in soybean

Photosynthesis, as the primary biochemical reaction for carbon fixation, provides the carbon skeletons for diverse secondary metabolites in plants. Here, we report that the transcription factors GmSTF1 and GmSTF2 regulate both photosynthesis and lignin biosynthesis in soybean (Glycine max). GmSTF1 and GmSTF2 directly bound to a TGACG motif in the promoter of the photosynthetic gene GmLHCA4 and a Z-box element in the promoter of the lignin biosynthetic gene GmCAD1, activating their transcription. Loss-of-function mutants (gmstfs-dm) displayed light-green leaves with reduced chlorophyll levels, photosynthetic rates, soluble sugar contents, and lignin contents. Conversely, transgenic soybean plants overexpressing these genes (GmSTF1-YFP and GmSTF2-YFP) showed enhanced chlorophyll accumulation, photosynthetic efficiency, soluble sugar production, and lignin deposition. Our findings identify GmSTF1 and GmSTF2 as critical regulators of carbon assimilation and lignin production in soybean.