Proline metabolism and phenylpropanoid pathway act independently in conferring resistance against yellow mosaic virus infection in black gram

Yellow mosaic virus (YMV) transmitted by whitefly (Bemisiatabaci) infects the leaves of black gram only during the kharif season, causing yellow mosaic disease (YMD)and the incidence of infections absent during the spring season. The main objective of the present investigation was to study the regulation of the phenylpropanoid pathway involved in the biosynthesis of secondary metabolites along with proline metabolizing enzymes that regulate proline content to provide resistance against YMD in black gram. Two blackgram cultivars- KUG253 (highly susceptible to YMV), MASH114 (resistant), and their Cross(KUG253 × MASH114) were sown during the kharif and spring seasons. During the kharif season,YMD appeared only in leaves of the KUG253 cultivar, followed by severe leaf chlorosis. All three cultivars of the black gram did not show any disease symptoms during the spring season. MASH114 and Cross cultivars successfully survived despite the prevalence of disease during kharif season because of the efficient working of both the pathways. Being susceptible to YMV, the KUG253 cultivar could not maintain the flavanol content, control quinone toxicity, and regulate proline metabolizing enzymes. Hence it failed to resist the attack of the disease. The reciprocal regulation of prolinedehydrogenase(ProDH) with proline biosynthesizing enzymes such as ornithine aminotransferase (OAT), glutamate dehydrogenase (GDH),and Δ¹-pyrroline-5-carboxylate synthetase (P5CS) in cultivars during infection suggested that proline accumulation was initiated as a part of induced defense response against the YMV infection in blackgram. The observed independence of phenylpropanoid and proline metabolizing pathways in imparting resistance to YMV can be significant in virus-infected plants.