Caracterization of the biological activity of the AhpR system of Xylella fastidiosa

Abstract

Xylella fastidiosa is the etiological agent of a number of economically important phytopathogenic diseases such as citrus variegated chlorosis (CVC). Plants produce oxidants such as peroxides as a defense against microorganisms, which have developed antioxidant defenses such as AhpR (alkylhydroperoxide reductase). AhpR is composed of peroxiredoxin AhpC (alkylhydroperoxide reductase subunit A) and flavoprotein disulfide reductase AhpF (alkylhydroperoxide reductase subunit F). The AhpC activity is based on a preserved cysteine residue which, in the reduced form, is in thiolate state and is in disulfide state in the oxidized form. The reduction of AhpC is performed by AhpF, which is composed of three domains: the first shows similarity with thioredoxins (Trx) and the other two are similar to thioredoxin reductase (TrxR) domains. Trx is a disulfide reductase endowed by a CXXC motif. TrxR is similar to AhpF, however it does not contain a Trx domain. Intriguingly, AhpF produces H2O2 through NADH-oxidase activity, which is flavin-dependent but not cysteine-dependent. Results obtained by non-systematic assays by our group showed that NADH-oxidase activity is absent in TrxR's. Therefore, in principle, the absence of AhpC (an antioxidant) aggravates the NADH-oxidase (pro-oxidant) activity of AhpF. The present work has as its objective the characterization of the physiological role of AhpR system in Xylella fastidiosa. Among others aspects, the structure and roles of TrxR and AhpF of Xylella fastidiosa will be compared. We will also try to obtain mutant strains of Xylella fastidiosa by deleting the genes that code these proteins. This will be done with the support of Dra. Marilis do Valle Marques (ICB-USP)'s research group.