Differential responses of genes and enzymes associated with ROS protective responses in the sugarcane smut fungus

Abstract The fungal pathogen Sporisorium scitamineum causes sugarcane smut disease. Previously, we have shown that sugarcane plants resistant to smut induce ROS coinciding with a delay in fungal colonization. Here, we investigated whether the fungus modifies the enzymatic antioxidant system in vitro and when colonizing sugarcane tissues in response to ROS. In vitro, the exposure to ROS did not affect cell integrity, and a combination of superoxide dismutases (SOD) and catalases (CAT) were active. Also, in vitro, the fungus did not alter the expression of the transcriptional regulator Yap1 and the effector protein Pep1. The fungus activated a distinct set of enzymes when colonizing plant tissues. Instead of CAT, S. scitamineum induced glutathione peroxidase (Gpx) gene expression only when colonizing smut-resistant plants. Yap1 had an earlier expression when colonizing both smut-susceptible and -resistant plants, with no apparent correlation either with the expression of antioxidant genes sod, cat, and gpx, or external redox imbalance. The expression of the effector pep1 was induced only in smut-resistant plants, potentially in response to ROS. Collectively, these results suggest that S. scitamineum copes with oxidative stress by inducing different mechanisms depending on the conditions (in vitro/in planta) and intensity of ROS. Moreover, the effector Pep1 is responsive to the stress imposed only by the sugarcane resistant genotype.