Differential transcript profiling through cDNA-AFLP showed complexity of rutin biosynthesis and accumulation in seeds of a nutraceutical food crop (Fagopyrum spp.)

BACKGROUND: Buckwheat, consisting of two cultivated species Fagopyrum tataricum and F. esculentum, is the richest source of flavonoid rutin. Vegetative tissues of both the Fagopyrum species contain almost similar amount of rutin; however, rutin content in seed of F. tataricum are ~50 folds of that in seed of F. esculentum. In order to understand the molecular basis of high rutin content in F. tataricum, differential transcript profiling through cDNA-AFLP has been utilized to decipher what genetic factors in addition to flavonoid structural genes contribute to high rutin content of F. tataricum compared to F. esculentum. RESULTS: Differential transcript profiling through cDNA-AFLP in seed maturing stages (inflorescence to seed maturation) with 32 primer combinations generated total of 509 transcript fragments (TDFs). 167 TDFs were then eluted, cloned and sequenced from F. tataricum and F. esculentum. Categorization of TDFs on the basis of their presence/absence (qualitative variation) or differences in the amount of expression (quantitative variation) between both the Fagopyrum species showed that majority of variants are quantitative (64%). The TDFs represented genes controlling different biological processes such as basic and secondary metabolism (33%), regulation (18%), signal transduction (14%), transportation (13%), cellular organization (10%), and photosynthesis & energy (4%). Most of the TDFs except belonging to cellular metabolism showed relatively higher transcript abundance in F. tataricum over F. esculentum. Quantitative RT-PCR analysis of nine TDFs representing genes involved in regulation, metabolism, signaling and transport of secondary metabolites showed that all the tested nine TDFs (Ubiquitin protein ligase, ABC transporter, sugar transporter) except MYB 118 showed significantly higher expression in early seed formation stage (S7) of F. tataricum compared to F. esculentum. qRT-PCR results were found to be consistent with the cDNA-AFLP results. CONCLUSIONS: The present study concludes that in addition to structural genes, other classes of genes such as regulators, modifiers and transporters are also important in biosynthesis and accumulation of flavonoid content in plants. cDNA-AFLP technology was successfully utilized to capture genes that are contributing to differences in rutin content in seed maturing stages of Fagopyrum species. Increased transcript abundance of TDFs during transition from flowers to seed maturation suggests their involvement not only in the higher rutin content of F. tataricum over F. esculentum but also in nutritional superiority of the former.