A small species-specific effector from Colletotrichum graminicola that targets the host nucleus and aids in virulence at the early stages of infection
Résumé
The fungus Colletotrichum graminicola is the causal agent of maize anthracnose. Fungal effector proteins are important for disabling plant defense components and promote successful infection. We have identified C. graminicola effector protein 3 (CgEP3). Based on evolutionary analysis, we determined that CgEP3 is specific to C. graminicola. Also, the genomic region including CgEP3 did not have synteny with other closely related species of Colletotrichum. We propose that genomic rearrangements led to the evolution of a new gene, CgEP3. Using heterologous transient expression in tobacco plants, we discovered that CgEP3 is localized to the nucleus and cytoplasm of host cells. Transcriptional profiling and live cell imaging show that CgEP3 is specifically expressed in conidia and appressoria suggesting that it is functionally important at this time-point. CgEP3 null mutants had significantly reduced lesion size, appressorial penetration and biomass accumulation on maize leaves and stems but, internal appressoria pressure and development are normal. Complementation of the CgEP3 null mutant restored the wild-type phenotype. A transcriptomic analysis designed to understand
the plant responses to CgEP3 during the colonization of maize leaves revealed that several plant defense genes are suppressed by CgEP3. We propose that CgEP3 is a pre-penetration effector that can help the fungus to disable plant defenses during the early stages of
infection.