The citrus defense in response to phytopathogen Xylella fastidiosa

Xylella fastidiosa is a gram-negative bacterium that colonizes the xylem of plants, thereby causing diseases on several economically important crops, such as citrus variegated chlorosis (CVC) in sweet orange. The aims of this work were an investigation on the roots influence to CVC bacterium, as well as to verify whether compounds in the roots were associated with the citrus infection. To establish a representative chromatographic fingerprint for the roots of C. sinensis grafted on C. limonia cv. Pêra with and without CVC symptoms. Respective samples were individually analyzed using the established high performance liquid chromatography-diode array and liquid chromatography-ultraviolet-atmospheric pressure chemical ionizationmass spectrometric methods, and two peaks indicated the highest content among others with good resolution, and they were identified as xanthyletin and seselin, respectively. Thus, a HPLC-UV method was developed for quantifying both in roots, with a good linearity. The quantification method was applied to Citrus with and without CVC symptoms after X. fastidiosa infection (Figure 1). Xanthyletin showed a significant increase (44%) in its amount in symptomatic roots. Increased biosynthesis of this metabolite may represent a plant defense strategy in response to pathogen attack, since this compound showed antimicrobial activity on X. fastidiosa growth (MIC 34 nM). Our studies open up possibilities for engineering citrus enzymes to increase levels of xanthyletin and thereby enhance resistance against X. fastidiosa, and also show a model substance used by the plant itself as a defense mechanism, with the potential to become a bactericide.