Walter A. Vargas, José M. Sanz Martín, Michael R. Thon and Serenella A. Sukno. 11 th European Congress on Fungal Genetics. Marburg, Germany, 30 March – 2 April 2012
Fungi secrete effectors that alter the host’s structure and function. Colletotrichum graminicola is the causal agent of maize anthracnose, which causes severe crop losses worldwide. To better understand disease development, we are studying novel effector proteins that are expressed during infection. We identified a gene encoding a putative effector protein by searching for proteins that contain secretion signal peptides as well as nuclear localization signals (NLS). In addition to the signal peptide and NLS, the protein has a highly basic isoelectric point and seven nearly identical internal repeated motifs. A BLAST search of the predicted protein sequence found no homologs in public databases, suggesting that it is unique to C. graminicola. We performed time-course assays for transcript abundance using RT-PCR as well as in situ experiments using transcriptional fusions of the promoter with gfp as a reporter gene. These studies revealed that the gene is expressed at early stages of host colonization, mainly in primary hyphae. We constructed null mutants by gene replacement and performed pathogenicity assays on maize seedlings. Anthracnose development was severely impaired on maize plants inoculated with mutant strains demonstrating that the gene is crucial for full pathogenicity of C. graminicola on maize. Based on our findings, we conclude that the gene encodes a novel fungal pathogenicity factor that we call CgEP1 (C. graminicola Effector Protein 1.) Results of in planta subcellular localization of the mature protein will be also presented.