Botrytis cinerea BcNma is involved in apoptotic cell death but not in stress adaptation

Apoptotic-like programmed cell death (PCD) occurs naturally in fungi during development and might also be induced by external conditions. Candidate apoptotic genes have been characterized in several model fungal species but not in plant pathogenic fungi. Here we report on the isolation and characterization of BcNMA, an orthologue of the human pro-apoptotic gene HtrA2 from the plant pathogen Botrytis cinerea. The predicted BcNma protein shows high homology to the previously characterized Nma111p from Saccharomyces cerevisiae and despite some structural differences it complemented the function of Nma111p in Δnma111 mutant strains. BcNMA-over-expression and mutant strains had enhanced or reduced appearance of apoptotic markers, respectively. However there was no difference in growth response of the wild type and BcNMA-transgenic strains to application of various stresses, and the effect on pathogenicity was marginal in both the over-expression and mutant strains. When considered together these results suggest that although BcNma has a pro-apoptotic activity, it is not a major regulator of apoptosis. The protein probably has additional roles that are unrelated to apoptosis, which lead to the pleotrophic phenotype of the transgenic strains and lack of a clear effect on stress adaptation and pathogenicity.