Exocyst subunit BcSec3 regulates growth, development and pathogenicity in Botrytis cinerea

Botrytis cinerea is a saprophytic plant pathogenic fungus that can infect a variety of crops and cause gray mold, which leads to huge losses worldwide. The role of exocyst in fungal pathogenicity is being revealed. In this study, homologous recombination technology was used to knock out the exocyst subunit BcSec3 of B. cinerea, and it was found that the BcSec3 subunit plays a crucial role in the growth and pathogenicity of B. cinerea. Compared with the wild-type strain B05.10, the mycelial growth ability of the BcSec3 deletion strain was reduced by up to 49.8%, the conidia production capacity of the deletion strain was severely lost, and no sclerotia was formed. The polygalacturonase, is one of plant cell wall hydrolases, whose activity in BcSec3 deletion strain was significantly reduced. In the tomato leaves infection assay in vitro, the lesion area caused by the BcSec3 deletion strain was only 20% of the wild type after 5 days of infection. Observation by light microscope showed that the morphology of BcSec3 deletion strain mycelium was significantly changed, the mycelium became thinner and deformed, and the polarity growth was not obvious. Further observation with laser confocal microscopy and transmission electron microscopy was conducted. It was found that compared with the wild type, the number of vesicles in BcSec3 deleted cells reduced and localization and distribution of vesicles changed. In mutant cell, vesicles relatively concentrated in the cytoplasm, while in wild-type cell mainly concentrated inside the cell membrane. These evidences indicate that the exocyst subunit BcSec3 plays an important role in the growth, development and pathogenicity of B. cinerea.