Enhanced Resistance Against a Broad Spectrum of Fungal Pathogens and Reniform Nematodes in Transgenic Cotton Plants Expressing an Arabidopsis NPR1 Gene

Cotton crop suffers severe losses every year due to a wide range of fungal/bacterial pathogens and nematodes.  Given its susceptibility to various pathogens, it is important to obtain a broad-spectrum resistance in cotton.  One of the possible means to achieve this goal is by utilizing one or more transgene(s) whose expression has been shown to confer tolerance/resistance to diseases.  In some plant species, overexpression of the Non-expressor of Pathogenesis-Related genes-1 (NPR1) has been shown to confer resistance to several fungal and bacterial diseases with apparently minimal or no pleiotropic effects.  We have now evaluated the usefulness of this approach in cotton by constitutive expression of the Arabidopsis (Arabidopsis thaliana) NPR1 gene.  Several NPR1-expressing transgenic lines were examined under growth chamber/greenhouse conditions and found to exhibit significant tolerance to Verticillium dahliae (isolates TS-2 and EZ-2), Fusarium oxysporum f. sp. vasinfectum (isolate Fov11), Rhizoctonia solani, Thielaviopsis basicola, and Alternaria alternata.  Interestingly, the transformants also showed significant resistance to reniform nematodes. Transcriptional and biochemical analyses of the defense response showed that when challenged with a pathogen (or certain systemic acquired resistance-inducing chemicals), the transgenic lines exhibit a stronger and faster induction of most of the defense-related genes/enzymes compared to the wild-type plants.  Importantly, the basal activities of the defense-related genes and enzymes in the uninduced transformants were no different than those of their non-transgenic counterparts.  This implies that plants incur little or no metabolic cost associated with the expression of this transgene.  Our investigation provides strong evidence supporting the role of NPR1 as an important part of the plant defense system and suggests that its overexpression can be used to achieve broad-spectrum resistance to pathogens in cotton.