Molecular cloning of a catalase cDNA from Nicotiana glutinosa L-and its repression by tobacco mosaic virus infection

Recent reports revealed that catalase has a role in the plant defense mechanism against a broad range of pathogens through being inhibited by salicylic acid (SA), During an effort to clone disease resistance-responsive genes, a cDNA encoding catalase (Ngcat1; Nicotiana glutinosa cat1) was isolated from a tobacco cDNA library. In N, glutinosa, catalase is encoded by a small gene family. The deduced amino acid sequence of the Ngcat1 cDNA has 98% homology with the cat1 gene of N. plumbaginifolia. The Ngcat1 expression is controlled by the circadian clock, and its mRNA level is the most abundant in leaves. Both the expression of Ngcat1 mRNA and its enzyme activity in the tobacco plant undergoing a hypersensitive response (HR) to TMV infection were repressed. The repression of the mRNA level was also observed following treatment with SA, These results imply that SA may act as an inhibitor of catalase transcription during the HR of tobacco. Cloning and expression of the Ngcat1 in tobacco following pathogen infection and SA treatment are presented.