Isoflavone phytoalexins in root exudates participate in mediating the resistance of common bean Phaseolus vulgaris to Phytophthora sojae

Abstract

AbstractCommon bean (Phaseolus vulgaris) cannot be infected naturally by Phytophthora sojae but produces a hypersensitive response (HR) under P. sojae inoculation. The goal of this study was to determine the roles of isoflavone phytoalexins in common bean root exudates in the resistance of common bean to P. sojae. The concentrations of kievitone, phaseollin and phaseollidin in the root exudates of common bean and their effects on P. sojae were measured. The transcriptomes of P. sojae responding to the phytoalexins were analysed. The three phytoalexins were included in the root exudates of three common bean cultivars at different concentrations and inhibited mycelial growth, oospore formation, zoospore chemotaxis and infection efficiency of P. sojae. The concentrations of the three phytoalexins in root exudates of three common bean cultivars were very low but increased significantly after inoculation with P. sojae. Kievitone probably inhibits P. sojae by promoting accumulation of abnormal transcripts, destroying mitochondria, inhibiting synthesis of ATP and protein, and reducing cell invasion and migration, making cells more sensitive to oxidative stress and slowing down proliferation and even apoptosis; phaseollin probably inhibits P. sojae by promoting the transcription level of some key genes in P. sojae that are associated with a reduction in migration and cell membrane damage; and phaseollidin probably inhibits P. sojae by promoting cell apoptosis. Our results suggest that kievitone, phaseollin and phaseollidin are involved in mediating the resistance of common bean to P. sojae through different mechanisms.