Upregulation of LmHxt1 gene is associated with reduced virulence of Leptosphaeria maculans on Brassica napus

Abstract

AbstractLeptosphaeria maculans is a fungal pathogen that causes heavy losses of Brassica napus crops. To develop novel means of plant protection it is necessary to understand the virulence mechanisms of pathogens. In this study we investigated a T-DNA insertion mutant of L. maculans that exhibited a hypovirulent phenotype (pHxt1ins). The mutant contains a single T-DNA insertion that affects expression of a single gene identified as a transmembrane hexose transporter (LmHxt1). This gene exhibited enhanced expression in the pHxt1ins mutant during in vitro cultivation. The excess of glucose in the cultivation medium lowered expression of LmHxt1 in the mutant line, suggesting that the gene might function as a sugar sensor. Lack of virulence of the pHxt1ins mutant in planta was observed using fluorescence microscopy in GFP labeled lines ruling out asymptomatic growth and showing inability to successfully colonize the apoplastic space of B. napus. On the other hand, in vitro growth did not differ between pHxt1ins and control lines. Interestingly, the mutant showed altered mycelium morphology and a change in conidial germination. Overall, our results suggest that the LmHxt1 gene is a novel important virulence factor for L. maculans. We also propose pHxt1ins mutant as a tool to study the role of sugar transporters in fungal metabolism and pathogenesis.