Abstract
Citrus canker, caused by the bacterium Xanthomonas citri subsp. citri (Xcc), is a severe disease of citrus. Xcc presents broad spectrum of citrus hosts including economically important species whereas X. fuscans subsp. aurantifolii–type C (XauC) causes a milder disease and only infects Citrus aurantifolia. Trehalase catalyzes hydrolysis of the disaccharide trehalose, a sugar that has been reported to be related to Xcc pathogenicity. We expressed the recombinant gene product and assessed Xcc trehalase structural and kinetics data. The recombinant protein presented 42.7% of secondary structures in α-helix and 13% in β-sheets, no quaternary structure in solution, and Michaelis-Menten constant (KM) of 0.077 mM and Vmax 55.308 μMol glucose.min-1.mg protein-1 for trehalose. A Xcc mutant strain (XccΔtreA) was produced by gene deletion from Xcc genome. Enzymatic activity of trehalase was determined in Xcc, XauC and XccΔtreA cellular lysates, showing the highest values for XauC in in vitro infective condition and no activity for XccΔtreA. Finally, leaves of Citrus aurantifolia infected with XccΔtreA showed much more drenching and necrosis than those infected by wild type Xcc. We concluded that trehalase contributes to alleviate bacterial virulence and that inability for trehalose hydrolysis may promote higher Xcc infectivity.
Highlights
Citrus canker is one of the most important citrus diseases and causes reduced productivity and quality of citrus fruits, aggravated by the lack of effective measures to control and cure the disease [1]
Deconvolution of the circular dichroism (CD) spectrum of TreA (Fig 1) indicated 42.7% of secondary structures in α-helix and 13% in β-sheets, a expected composition given the extensive identity with the trehalase from E. coli, which has 47% of α-helices and 8% β-sheets [22]
The data obtained from size-exclusion chromatography (SEC, Fig 2) indicated that Xanthomonas citri subsp. citri (Xcc) TreA must be a monomer in solution
Summary
Citrus canker is one of the most important citrus diseases and causes reduced productivity and quality of citrus fruits, aggravated by the lack of effective measures to control and cure the disease [1]. Citri (Xcc) attack all known species of citrus and their hybrids, causing the most severe form of the disease (canker A). Aurantifolii type C (XauC) causes the less severe canker C that attacks a single host, Citrus aurantifolia [2, 3]. Canker A injuries the aerial parts of the plants, especially the leaves and the surface of fruits, causing disruption of the plant epidermis [1, 4]. Man is an important disease spreader through contaminated
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