Ras-associated protein PdRSR1 is essential for sterol synthesis and stress tolerance to response to prochloraz in...

Citrus green mold caused by the fungi Penicillium digitatum always brings out enormous economic losses during the postharvest period. In practice, this pathogen is generally controlled by the demethylation inhibitor (DMI) fungicides, but massive usage of DMIs leads to the increasing occurrence of resistant strains and concerns of public safety. Hence, it is vital to clarify the molecular mechanism of P. digitatum response to DMIs. In this study, we investigated the biological function of gene PdRSR1, the Rap1 protein of Ras GTPase family in P. digitatum. First, gene PdRSR1 was deleted and complemented in the principle of homologous recombination, and the deletion mutant ΔPdRSR1 showed highly reduced resistance to DMIs. The phenotypic assay indicated that strain ΔPdRSR1 had severe defects in osmotic stress tolerance and cell wall integrity, but the hyphal growth and pathogenicity were still normal. Compared with wild-type strain N1, the sterol and trehalose levels of strain ΔPdRSR1 were detected to be sharply declined with or without prochloraz-treated. The RT-qPCR analysis suggested that prochloraz did not influence the expression of PdRSR1, but suppressed it of PdRas1 and their activating proteins PdGAPs, which disturbed the transcription of downstream metabolism, including the MAPK signaling pathway, the synthesis of chitin, trehalose and sterol, and the activities of efflux transporters. Taken together, our work characterized that GTPase PdRSR1 is an essential target to prochloraz in P. digitatum, and provided a new insight of P. digitatum to response to prochloraz.