Overexpression of PIF4 affects plant morphology and accelerates reproductive phase transitions in soybean

Phytochrome-interacting factor 4 acts as a signalling hub for integrating multiple environmental cues like light and temperature. While the function of PIF4 in the model plant Arabidopsis has been studied, there is limited knowledge regarding the role of PIF4 in agronomically important legume crop soybean. Here, we employed a constitutive overexpression approach to functionally characterise a soybean PIF4 homolog, GmPIF4b in a determinate short-day cultivar, Bragg. Multiple sequence alignment of seven soybean PIF4 homologs (GmPIF4a-g) with Arabidopsis PIF4 revealed the presence of an active phytochrome-binding (APB) domain in the N-terminal region of six soybean PIF4 homologs. Cis-elements related to plant hormone biosynthesis, stress response, meristem and endosperm gene expression were located in the promoter region of soybean PIF4s. Interestingly, transgenic soybean plants carrying 35s::GmPIF4b::polyA construct showed reduced plant height, reduced leaf surface area, decreased branching, early flowering and faster transition from full-bloom flowering stage to full maturity stage without any decline in yield. Further, pod colour of transgenic soybean plants changed to dark brown, whereas wild-type plants showed tan or light brown pod colour. Clear hilum was observed in seeds obtained from transgenic plants as opposed to the dark or black hilum of wild-type seeds. Transcripts of soybean florigens GmFT2a and GmFT5a were also elevated in transgenic plants. Collectively, our results suggest that GmPIF4b overexpression could affect phenotypes related to plant morphology and reproductive stages in soybean, and can be used as a gene target for soybean improvement programmes to ensure future food security.

Automated summary

The overexpression of GmPIF4b in soybean plants led to reduced plant height, leaf surface area, branching, early flowering, and faster transition from full-bloom flowering to full maturity stage. Additionally, changes were observed in pod color and seed hilum characteristics. These findings suggest that GmPIF4b could be a valuable gene target for soybean improvement programmes focusing on plant morphology and reproductive stages.