Functional Analysis of the Trichoderma harzianum nox1 Gene, Encoding an NADPH Oxidase, Relates Production of Reactive Oxygen Species to Specific Biocontrol Activity against Pythium ultimum

The synthesis of reactive oxygen species (ROS) is one of the first events following pathogenic interactions in eukaryotic cells, and NADPH oxidases are involved in the formation of such ROS. Thenox1 gene ofTrichoderma harzianum was cloned, and its role in antagonism against phytopathogens was analyzed innox1 -overexpressed transformants. The increased levels ofnox1 expression in these transformants were accompanied by an increase in ROS production during their direct confrontation withPythium ultimum . The transformants displayed an increased hydrolytic pattern, as determined by comparing protease, cellulase, and chitinase activities with those for the wild type. In confrontation assays againstP. ultimum thenox1 -overexpressed transformants were more effective than the wild type, but not in assays againstBotrytis cinerea orRhizoctonia solani . A transcriptomic analysis using aTrichoderma high-density oligonucleotide (HDO) microarray also showed that, compared to gene expression for the interaction of wild-typeT. harzianum andP. ultimum , genes related to protease, cellulase, and chitinase activities were differentially upregulated in the interaction of anox1 -overexpressed transformant with this pathogen. Our results show thatnox1 is involved inT. harzianum ROS production and antagonism againstP. ultimum .