BcHnm1, a predicted choline transporter, modulates conidial germination and virulence in Botrytis cinerea.

Previous network-based comparative genomic analysis between major lifestyles of fungal plant pathogens highlighted that HNM1, a predicted choline transporter, is part of the necrotroph core-genome's functions. In this work we have generated and characterized deletion mutants and developed complemented strains for the HNM1 homolog (Bchnm1) in the necrotrophic model fungal plant pathogen Botrytis cinerea. The Bchnm1 deletion mutants exhibited reduced conidia germination and germ tube elongation. The functional activity of the Δbchnm1 deletion mutants was illustrated by reduced necrotic colonization of B. cinerea on tomato and French bean leaves. The role of BcHnm1 in germination was also supported by qRT-PCR results that illustrated increased Bchnm1 transcript levels during the early infection stages (at 16 h post inoculation) of the WT strain on tomato plant leaves, and during conidia germination (in-vitro). In line with the predicted function of BcHnm1 in choline transport, Δbchnm1 deletion mutant showed an attenuated choline import capacity. The potential role of choline in the WT B. cinerea was further demonstrated by an increase in conidia germination (by 100%) in the presence of 1 mM exogenous choline while growth in the presence of hemicholinium-3, an inhibitor of choline transporter, showed 40% inhibition in germination. In contrast to the WT, exogenous choline and the inhibitor did not affect conidia germination in the Δbchnm1 deletion mutants. Collectively, this study shows for the first time that BcHnm1, a predicted choline transporter, is important for conidial germination, germ tube elongation, response to exogenous choline, and virulence in plant pathogenic fungi.

MFS transporter from Botrytis cinerea provides tolerance to glucosinolate-breakdown products and is required for pathogenicity.

Glucosinolates accumulate mainly in cruciferous plants and their hydrolysis-derived products play important roles in plant resistance against pathogens. The pathogen Botrytis cinerea has variable sensitivity to glucosinolates, but the mechanisms by which it responds to them are mostly unknown. Exposure of B. cinerea to glucosinolate-breakdown products induces expression of the Major Facilitator Superfamily transporter, mfsG, which functions in fungitoxic compound efflux. Inoculation of B. cinerea on wild-type Arabidopsis thaliana plants induces mfsG expression to higher levels than on glucosinolate-deficient A. thaliana mutants. A B. cinerea strain lacking functional mfsG transporter is deficient in efflux ability. It accumulates more isothiocyanates (ITCs) and is therefore more sensitive to this compound in vitro; it is also less virulent to glucosinolates-containing plants. Moreover, mfsG mediates ITC efflux in Saccharomyces cerevisiae cells, thereby conferring tolerance to ITCs in the yeast. These findings suggest that mfsG transporter is a virulence factor that increases tolerance to glucosinolates.