Molecular and Functional Characterization of Key Regulatory Elements, FT and SOC1, Controlling Development of Flowering Traits in Brassica Species

摘要

Brassica is an economically important oilseed mustard crop; globally India ranks fourth in acreage and production albeit with lower per acre productivity. The failure to realize true harvest potential is mainly attributable to environmental onslaughts encountered by the crop in the field. Thus there is an urgent need to develop high yielding Brassica varieties capable of withstanding environmental stresses. Time to flower is an important trait in any crop as it marks the culmination of life-cycle of a plant. One of the ways to mitigate losses occurring in the field is to develop early flowering cultivars with shorter life spans. Genes regulating flowering time are well described in model plant system A. thaliana, and I extrapolated this knowledge to Brassicas which belong to the same mustard family. Keeping Brassica crop improvement in mind, my research problem "Molecular and functional characterization of key regulatory elements like FT and SOC1 controlling development of flowering traits in Brassica species" was taken up. My doctoral research is the first ever study that reports isolation and characterization of two important candidate genes, FT and SOC1, from Indian cultivars of Brassica. Analysis of expression pattern of FT and SOC1 in Brassica suggested their role in control of flowering time. Further, FT expression was shown to follow a circadian rhythm in "long days" in B. juncea. Numerous sequence variants were isolated from diverse cultivars of six Brassica species and displayed likely evolutionary trajectories leading to their diversification. In-silico synteny analysis confirmed the differential gene fractionation of the three B. rapa subgenomes (LF, MF1 and MF2). Detailed phylogenetic analyses, led to the identification of divergent Brassica FT and SOC1 variants. Functional characterization using gain-of-function approach showed drastic to moderate effects in terms of earliness in flowering time, in transgenic backgrounds. As a complementary strategy, I also designed artificial miRNA based gene silencing technology for specific down-regulation of Brassica FT and SOC1 and demonstrated expected delay in flowering time. Taken together, the data from mutant analysis confirmed the role of Brassica FT and Brassica SOC1 in flowering time control. In summary, my doctoral research led to identification of extensive natural variation in FT and SOC1 gene, with conserved role in control of flowering time in Indian Brassicas. This genetic diversity is a valuable natural resource for Brassica crop improvement programs and generation of climate resilient crops displaying modulated flowering time.