Transcriptome analysis reveals abscisic acid enhancing drought resistance by regulating genes related to flavonoid metabolism in pigeon pea

Abscisic acid (ABA) plays an important role in drought resistance of plants. Plants subjected to drought stress often produce a large number of secondary metabolites. More and more studies indicate that secondary metabolites are directly related to plant stress resistance. However, there are few reports about the influence of ABA regulating secondary metabolism on drought. In our study, we found that as a pioneer tree species in karst landforms, the drought resistance can also be improved by ABA. ABA can reduce the stomatal opening of pigeon pea under drought stress and reduce the influx of H+ from the root tip. At the same time, we found that in ABA-treated pigeon pea, flavonoid metabolites accumulate in large amounts, especially genistein, genistin and pterostilbene. Through transcriptome sequencing analysis, it was found that after ABA treatment, flavonoids biosynthesis pathways changed significantly; among them, the key enzyme genes CHS, HIDH and ROMT in the biosynthesis pathway of genistein, genistin and pterostilbene were significantly up-regulated. According to the co-expression analysis in the transcriptome data, we screened that multiple MYB and bHLH transcription factors may be involved in the regulation of flavonoid accumulation. And the biosynthetic genes contained binding sites of related transcription factors. Through RT-PCR, we further analyzed the expression of MYB, bHLH and related biosynthetic genes after ABA treatment at different times, and found that they were all regulated by ABA. By High Performance Liquid Chromatography (HPLC) analysis, we found the increase of genistein, genistin and pterostilbene content in pigeon pea treated with ABA under drought stress. Through hairy root transgenic analysis, We found that CcMYB114 regulate drought resistance by modulating the expression of CcHIDH1 and CcHIDH3, and then regulating genistein and genistin accumulation in pigeon pea. This study provides evidence to analyze the regulation of ABA in pigeon pea on the metabolism of flavonoids and thus affect its drought resistance.