Functional characterization of a Colletotrichum graminicola fungalysin with a role in virulence

JOSÉ M. SANZ MARTÍN; WALTER A. VARGAS; VINICIO ARMIJOS-JARAMILLO; MICHAEL R. THON ; SERENELLA A. SUKNO

Conferencia; 12th European Conference in Fungal Genetics; 2014

Plants produce a wide array of pathogenesis-related(PR) proteins to defend themselves against microbial invaders. Some of these PR proteins are hydrolytic enzymes that target fungal cell walls, such as chitinases. Fungi also secrete awide range of effector proteins to manipulate the plant immune system. Recently, fungal effectors have been identified that interfere with chitin-triggered immunity, protecting the fungal hyphae against hydrolysis by chitinases or sequestering the chitinoligosaccharides and preventing chitin binding to the receptor. In thisstudy, we describe CgEP2 (Colletotrichum graminicola EffectorP rotein 2), a 640 aa secreted protein in the maize hemibiotroph Colletotrichum graminicola, with an important role in virulence. CgEP2 is a fungalysin highly conserved in diverse fungi that binds plant produced class IV chitinases, and directly catalyzes their post-translational modification by enzymatic activity. Using transcriptional fusions of the gene promoter with GFP as well as qPCR assays at different time points during infection, we show that the gene expression is activated specifically when the fungus switches from biotrophic to necrotrophic growth. We constructed null mutants by gene replacement and performed pathogenicity assays in maize and observed reduced lesion sizes on leaves and reduced colonization of roots, showing that CgEP2 has a role in C. graminicola virulence. Biochemical analysis of chitinase activity with the null mutant confirms the lack of ability to degrade this substrate. Our results show that CgEP2 plays a role in plant infection and host colonization and could be important in the lifestyle change of C. graminícola.