Elevated genetic variation within virulence-associated Botrytis cinerea polygalacturonase loci

Botrytis cinerea, or gray mold, is a necrotrophic fungal pathogen of hundreds of plant species. The genetic diversity of B. cinerea may contribute to its broad host range; however, the level and structure of genetic variation at pathogenesis- associated loci has not been described. B. cinerea possesses six distinct cell-wall-degrading polygalacturonases (PGs), enzymes of demonstrated importance to pathogenesis and interaction with host plant defenses. Sequencing a collection of 34 B. cinerea isolates at three PG-encoding loci, BcPG1, BcPG2, and BcPG3, revealed limited evidence of host-mediated genetic subdivision within loci, yet suggested differences in the action of evolutionary forces among loci. BcPG1 and BcPG2 are highly polymorphic, particularly when compared with previously published data from nonpathogenicity loci, whereas BcPG3 is relatively conserved. Sequence variation at BcPG1 and BcPG2 did not appear to be associated with virulence on Arabidopsis leaves; however, BcPG2 variation showed a statistically significant association with growth rate on pectin. Rather than providing evidence for host-mediated genetic subdivision at individual PG loci, our data support specialization among PGs and the potential diversification of PGs interacting directly with host defenses.