Analysis of the Alternaria solani genome reveals effector protein candidates that trigger cell death in potato

The fungal genus Alternaria consists of saprophytes as well as important necrotrophic plant pathogens. Early blight is a serious disease of potato that is caused by Alternaria solani and closely related Alternaria species. In A. alternata, host specific toxins have been identified that enable it to infect specific hosts, but, as of now, it is still unknown which genes from A. solani are involved in causing early blight. We used Single Molecule, Real-Time sequencing technology to sequence the A. solani genome to identify genes that contribute to the infection of potato. The finished genome sequence of A. solani was compared with the genomes of related Alternaria that are not pathogenic on potato, leading to the identification of proteinaceous effector candidates. Transient expression of these putative effectors in potato plants showed that some of them can trigger cell death in susceptible hosts, suggesting a role for these genes in disease development. In parallel, we have performed a wide screen of wild potato accessions for resistance to A. solani, which resulted in the identification of Solanum genotypes with high levels of resistance. Thus, we provide a promising starting point to explore the roles of proteinaceous effectors, and the underlying molecular mechanisms, in causing susceptibility or resistance of potato plants to early blight. By screening for responses to the effector candidates that were identified in our study, the mapping of host susceptibility factors or resistance genes will be facilitated.