Characterization of a major facilitator superfamily transporter in Shiraia bambusicola

Reactive oxygen species (ROS) generated by photo-activated hypocrellin from Shiraia bambusicola are detrimental to cellular macromolecules. However, S. bambusicola can still maintain excellent morphology during continuous hypocrellin production, indicating an extraordinary autoresistance system that protects against the harmful ROS. In this study, a major facilitator superfamily transporter (MFS) was isolated from S. bambusicola and deleted using the clustered regularly interspaced short palindromic repeat sequences (CRISPR)/Cas9 system. The ΔMFS mutant abolished hypocrellin production and was slightly sensitive to 40-μM hypocrellin, while the ΔMFS compliment strain restored hypocrellin production and resistance. Hypocrellin treatment also enhanced the relative expression of MFS in wild-type S. bambusicola. Subsequent pathogenicity assays showed that MFS deletion reduced damage to bamboo leaves. By contrast, restoration of hypocrellin production in the MFS compliment strain generated similar necrotic lesions on bamboo leaves to those observed with the wild-type strain. These results revealed that the identified MFS is involved in efflux of hypocrellin from cells, which reduces the hypocrellin toxicity. Furthermore, hypocrellin contributed to the virulence of S. bambusicola on bamboo leaves. These findings could help to reduce plant loss by disrupting hypocrellin biosynthesis in S. bambusicola, or overexpressing the associated resistance gene in transgenic plants.