RESUMO
SOC1, a MADS-box type II transcription factor, integrates environmental and endogenous cues to promote flowering in angiosperms. Recent reports implicating SOC1 in roles beyond floral transition prompted functional characterization of SOC1 in polyploid rapeseed mustard genomes. Gene characterization in Brassicas necessitates analysis of composite homeolog function. While insertional mutagenesis is untenable in Brassicas owing to gene redundancy, gain-of-function approach entails serial characterization of individual homeologs. Herein, we demonstrate modulated floral promotive effects in natural variants of Brassica SOC1 and provide lateral branching as a probable outcome of polyploidy-induced gene diversification. Ectopic expression of two B genome specific SOC1 variants in Arabidopsis thaliana resulted in differential floral acceleration and manifestation of multiple vegetative rosettes. Characterization of composite homeolog function in B. juncea via introgression of Brassica SOC1 specific artificial miRNA, designed to target homeologs, also exhibited modifications in floral transition and lateral branching. Comprehensive analysis of field performance of B. juncea transgenics displayed altered fitness across 11 agronomic traits. Crucially, reduced SOC1 levels directly impacted two developmental traits, namely, flowering time and number of lateral branches which in turn influenced several dependent agronomic traits. While delayed flowering and crop maturity resulted in altered fatty acid composition with higher SFA and lower PUFA in transgenics relative to controls, reduction in overall count of lateral branches caused a concomitant decrease in silique count which ultimately impacted total seed yield in transgenics. Statistical analysis revealed number of secondary branches as the most critical trait influencing seed yield. Based on our findings, we propose enhancing levels Brassica SOC1, a key target, for achieving earliness in flowering, improved seed yield and oil quality, and studying trait trade-offs.