Plant cell localization of candidate effector proteins from Sporisorium scitamineum, the sugarcane smut pathogen

Abstract

Sugarcane (Saccharum spp.) has long been recognized as one of the world's most efficient crop in converting solar energy into chemical harvestable energy, as sucrose and biomass. However, its productivity is compromised by several diseases, including the smut, caused by the biotrophic basidiomycete Sporisorium scitamineum. Efforts to elucidate the global plant response to pathogen as well as smut pathogenicity mechanisms were made by our group using RNAseq technology in a compatible interaction at two time points: shortly after inoculation and later, when the whip appeared and disease symptoms were evident. Data analysis revealed that early (5 days after inoculation) general plant immunity is down-regulated, while epigenetic mechanisms and genes related to meristem identity are up-regulated; while late interaction (after whip development) is characterized by hormonal imbalance and changes in carbon distribution. This behavior indicates that smut pathogen is able to avoid eliciting PTI and either cope with or suppress it using mechanisms such as inactivation of toxic metabolites or secretion of fungal effectors. These effectors are small secreted pathogen proteins that in compatible interactions manipulate plant processes to its own advantage. RNAseq and genomic data were used in our lab to create hypothesis on the presence of candidate effector proteins by analyzing differential gene expression of S. scitamineum growing in plant in comparison to its growth in culture medium. The analysis revealed a set of genes from the predicted pathogen secretome with no known function that are among the genes highly expressed in plant, differentially expressed or only expressed in planta. Due to their predicted protein size, lack of GPI-anchor sequences and presence of signal peptide make them good targets for functional analyzes. Functional description of effectors is not an easy task, but allow us to improve the chances in locating resistance genes. The aim of this project is to determine the host compartment cells targeted by S. scitamineum candidate effectors using N. benthamiana transient expression. We chose the lab of Dr. Savithramma P. Dinesh-Kumar for his expertise and long term experience that can help us to quick and efficiently work our hypothesis. The knowledge acquired during the internship will improve the ways of working in Dr. Claudia Monteiro-Vitorello's laboratory which is leaning towards functional studies of plant-pathogen interaction. (AU)