Undergraduate Student University of Kentucky Danville, Kentucky
Body of Abstract: Colletotrichum graminicola is an economically devastating fungus that causes anthracnose leaf blight, stalk rot, and top die-back in maize. As a hemibiotrophic pathogen, C. graminicola uses two methods of nutrient acquisition. The fungus first invades living cells biotrophically and later switches to necrotrophy. This transition from biotrophy to necrotrophy is attributed to the up regulation of genes encoding cell wall degrading enzymes (CWDEs). CWDEs also play roles in host-pathogen communication and are critical to promoting disease susceptibility. A mutant strain of C. graminicola (MT) lacks pathogenicity to maize leaves and stalks due to a mutation in the 3’UTR of a gene (Cpr1) encoding a homolog of the SPC22/23 subunit of the signal peptidase complex. Despite being able to germinate and penetrate host cells, the MT is interrupted early in infection, so it never shifts to necrotrophy, produces lesions, or sporulates. To investigate the mechanism behind the non-pathogenicity of the MT, it was hypothesized that the MT is deficient in its ability to secrete CWDEs in planta during the transition to necrotrophy. Hydrolase activity against plant cell wall polymers in culture was quantified and compared via reducing-sugar assays and utilization of chromogenic substrates. Individual CWDEs, such as pectate lyase, were also visualized as fluorescent fusions and quantified in the wild type (WT), MT, and complemented MT (C-MT) strains in living or killed maize leaf sheaths, and in culture. Pectate lyase plays a critical role in pectin degradation and was selected due to its high expression in transcriptome studies. Results indicated that hydrolase activity and enzyme secretion by the MT were equivalent to those of the WT and C-MT, suggesting that the lack of pathogenicity in the MT is not due to an inability to secrete CWDEs. Understanding fungal pathogenicity mechanisms is crucial to develop plant resistance to fungal pathogens.