Identification and analysis of flavonoid pathway genes in responsive to drought and salinity stress in Medicago truncatula

Flavonoid compounds are widely present in various organs and tissues of different plants, playing important roles when plants are exposed to abiotic stresses. Different types of flavonoids are biosynthesized by a series of enzymes that are encoded by a range of gene families. In this study, a total of 63 flavonoid pathway genes were identified from the genome of Medicago truncatula. Gene structure analysis revealed that they all have different gene structure, with most CHS genes containing only one intron. Additionally, analysis of promoter sequences revealed that many cis-acting elements responsive to abiotic stress are located in the promoter region of flavonoid pathway genes. Furthermore, analysis on M. truncatula gene chip data revealed significant changes in expression level of most flavonoid pathway genes under the induction of salt or drought treatment. qRT-PCR further confirmed significant increase in expression level of several flavonoid pathway genes under NaCl and mannitol treatments, with CHS1, CHS9, CHS10, F3'H4 and F3'H5 genes showing significant up-regulation, indicating they are key genes in response to abiotic stress in M. truncatula. In summary, our study identified key flavonoid pathway genes that were involved in salt and drought response, which provides important insights into possible modification of flavonoid pathway genes for molecular breeding of forage grass with improved abiotic resistance.