Fungal Mitochondrial DNases: Effectors with the Potential to Activate Plant Defenses in Nonhost Resistance

Hadwiger, L. A., and Polashock, J. 2013. Fungal mitochondrial DNases: Effectors with the potential to activate plant defenses in nonhost resistance. Phytopathology 103:81-90. Previous reports on the model nonhost resistance interaction between Fusarium solani f. sp. phaseoli and pea endocarp tissue have described the disease resistance-signaling role of a fungal DNasel-like protein. The response resulted in no further growth beyond spore germination. This F solani f. sp. phaseoli DNase gene, constructed with a pathogenesis-related (PR) gene promoter, when transferred to tobacco, generated resistance against Pseudomonas syringe pv. tabaci. The current analytical/theoretical article proposes similar roles for the additional nuclear and mitochondria] nucleases, the coding regions for which are identified in newly available fungal genome sequences. The amino acid sequence homologies within functional domains are conserved within a wide array of fungi. The potato pathogen Verticillium dahliae nuclease was divergent from that of the saprophyte, yeast; however, the purified DNase from yeast also elicited nonhost defense responses in pea, including pisatin accumulation, PR gene induction, and resistance against a true pea pathogen. The yeast mitochondrial DNase gene (open reading frame) predictably codes for a signal peptide providing the mechanism for secretion. Mitochondrial DNase genes appear to provide an unlimited source of components for developing transgenic resistance in all transformable plants.