Unraveling the regulatory role of miRNAs responsible for proanthocyanidin biosynthesis in the underutilized legume Psophocarpus tetragonolobus (L.) DC.

The underutilized legume winged bean (Psophocarpus tetragonolobus (L.) DC.) is deposited with various degrees of proanathocyanidin (PA) or condensed tannin (CT) on its seed-coat. PA content of two different lines of P. tetragonolobus was estimated and accordingly they were denoted as high-proanthocyanidin containing winged bean (HPW) and low-proanthocyanidin containing winged bean (LPW). The level of PA-content varied as 59.23 mg/g in HPW and 8.68 mg/g in LPW when estimated through vanillin-HCl assay. The identification and quantification of catechin and epigallocatechin gallate were estimated in a range of 63.8 mg/g and 2.3mg/g respectively in HPW whereas only epigallocatechin gallate was reported in LPW line with a value of 3 mg/g. A comparative miRNA profiling of the leaf-tissues of these contrasting lines of P. tetragonolobus revealed a total of 139 mature miRNAs. Isoforms of known novel miRNAs were also identified in this study. Differentially expressed miRNAs e.g., miR156, miR396, miR4414b, miR4416c, miR894, miR2111 and miR5139 were validated through qRT-PCR analysis. Target prediction of the identified miRNAs especially miR156, miR396, miR4416b shows that they have a potential role in the proanthocyanidin biosynthesis of P. tetragonolobus. The study will provide the basis for understanding the role of miRNAs in regulating the biosynthesis of proanthocyanidin.