Tyagi Shikha, Sri Tanu, Singh Anupama, Mayee Pratiksha, Shivaraj S M, Sharma Prateek, Singh Anandita
Department of Biotechnology, TERI School of Advanced Studies, 10, Institutional Area, Vasant Kunj, New Delhi, 110070, India.
Department of Research, Ankur Seeds Pvt. Ltd., 27, New Cotton Market Layout, Nagpur, Maharashtra, 440018, India.
Funct Integr Genomics. 2019 Jan;19(1):43-60. doi: 10.1007/s10142-018-0626-8. Epub 2018 Jun 25.
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.
SOC1是一种MADS-box II型转录因子，它整合环境和内源信号以促进被子植物开花。最近有报道表明SOC1在花期转换之外还发挥其他作用，这促使人们对多倍体油菜基因组中的SOC1进行功能表征。在芸苔属植物中进行基因表征需要分析复合同源基因的功能。由于基因冗余，在芸苔属植物中进行插入诱变是不可行的，而功能获得法需要对单个同源基因进行系列表征。在此，我们证明了芸苔属植物SOC1自然变体中花促进效应的调节，并表明侧枝形成可能是多倍体诱导的基因多样化的结果。在拟南芥中异位表达两个B基因组特异性SOC1变体导致了不同程度的花期加速和多个莲座叶丛的出现。通过导入针对同源基因设计的芸苔属植物SOC1特异性人工miRNA来表征芥菜型油菜中复合同源基因的功能，也显示出花期转换和侧枝形成的改变。对芥菜型油菜转基因植株田间表现的综合分析显示，11个农艺性状的适应性发生了变化。至关重要的是，SOC1水平降低直接影响了两个发育性状，即开花时间和侧枝数量，进而影响了几个相关的农艺性状。虽然转基因植株中开花延迟和作物成熟导致脂肪酸组成改变，饱和脂肪酸含量较高，多不饱和脂肪酸含量较低，但侧枝总数减少导致角果数随之减少，最终影响了转基因植株的种子总产量。统计分析表明，二级分枝数量是影响种子产量的最关键性状。基于我们的研究结果，我们建议提高关键靶点芸苔属植物SOC1的水平，以实现花期提前、提高种子产量和油质，并研究性状权衡。
