Comparative analyses of secreted proteins from the phytopathogenic fungus Verticillium dahliae in response to nitrogen starvation

The soilborne fungus Verticillium dahliae is the major pathogen that causes the verticillium wilt disease of plants, which leads to huge economic loss worldwide. At the early stage of infection, growth of the pathogen is subject to the nutrition stress of limited nitrogen. To investigate the secreted pathogenic proteins that play indispensable roles during invasion at this stage, we compared the profiles of secreted proteins of V. dahliae under nitrogen starvation and normal conditions by using in-gel and in-solution digestion combined with liquid chromatography–nano-electrospray ionization tandem mass spectrometry (LC–nanoESI-MS). In total, we identified 212 proteins from the supernatant of liquid medium, including 109 putative secreted proteins. Comparative analysis indicated that the expression of 76 proteins was induced, whereas that of 9 proteins was suppressed under nitrogen starvation. Notably, 24 proteins are constitutively expressed. Further bioinformatic exploration enabled us to classify the stress-induced proteins into seven functional groups: cell wall degradation (10.5%), reactive oxygen species (ROS) scavenging and stress response (11.8%), lipid effectors (5.3%), protein metabolism (21.1%), carbohydrate metabolism (15.8%), electron–proton transport and energy metabolism (14.5%), and other (21.0%). In addition, most stress-suppressed proteins are involved in the cell-wall remodeling. Taken together, our analyses provide insights into the pathogenesis of V. dahliae and might give hints for the development of novel strategy against the verticillium wilt disease.