Involvement of effector proteins in Penicillium expansum-apple fruit interactions

Penicillium expansum regarded as one of the most important postharvest rots of apple fruit and of great concern to fruit processing industries due to secretion of potent mycotoxins. Elucidating the pathogenicity mechanisms of this pathogen is of utmost importance for the development of effective and safe management strategies. We found that P. expansum secretes proteins during apple infection that suppress resistance related ROS production in the apple wounds. These findings suggest the possibility that effector-proteins may play an important role in the P. expansum interaction with the host. In the current study, bioinformatic tools were used to develop a pipeline to predict potential effector genes in P. expansum and study their role in pathogenicity on apples. Features such as secretion, differential expression in planta during infection, small size, and large number of cysteines as well as information available in databases on known effectors were used to predict genes relevant to processes associated with the infection of apples by P. expansum. Applying the effector-prediction pipeline to the secretome of P. expansum revealed 103 enzymes that degrade cuticle-building polymers, carbohydrates, peptides, lipids and phospholipids, as well as 106 potential effector proteins. Among the predicted effectors that were identified, 47 of them have homology to known effectors. LysM proteins, NEP-1-like proteins, small-cystein rich (SCR) proteins with unknown function and subtilisin-related Peptidase S8 were characterized and functionaly analyzed. We found several putative effectors that have an effect on the pathogenicity and virulence of P. expansum on apples as well as proteins with pleiotropic effect affecting growth rate, morphology and sporulation.