S -nitrosothiols and Plant Defenses

Abstract

Analysis of plants ( Arabidopsis ) lacking S -nitrosoglutathione reductase (GSNOR) revealed an important role for the enzyme in multiple processes that mediate the plant immune response and resistance to pathogens. The enzyme metabolizes S -nitrosoglutathione, which appears to function in S -nitrosylation of proteins--a covalent modification that can alter protein function. Feechan et al. used T-DNA insertions to create Arabidopsis mutants that expressed increased amounts of GSNOR or lacked expression of the protein and explored the effects on resistance to pathogens. Plants expressing more GSNOR showed increased resistance to bacterial pathogens. Plants express resistance (R) gene products that specifically recognize avirulence protein from pathogens. Such resistance to a bacterial pathogen, Pst DC300, was diminished in plants lacking GSNOR. Plants also have two more general disease resistance mechanisms, which the authors call a basal disease resistance and nonhost disease resistance. Loss of GSNOR also enhanced these defense mechanisms. Sialic acid (SA) is a plant signaling molecule that promotes expression of genes that participate in defense responses. Such SA-dependent gene expression was reduced and delayed in plants lacking GSNOR. Thus, GSNOR appears to be a negative regulator of multiple plant defense responses. This contrasts with the role of vertebrate GSNOR, which appears to inhibit inflammatory responses. The authors note that control of GSNOR activity provides a possible target for modification of plant disease responses. A. Feechan, E. Kwon, B.-W. Yun, Y. Wang, J. A. Pallas, G. J. Loake, A central role for S -nitrosothiols in plant disease resistance. Proc. Natl. Acad. Sci. U.S.A. 102 , 8054-8059 (2005). [Abstract] [Full Text]