CsFAO3 enhances citrus canker severity by regulating leaf cuticular wax production in Citrus sinensis

•The promoter activity of CsFAO3 is enhanced after Xanthomonas citri pv. citri induction.•Overexpression of CsFAO3 increases the susceptibility of transgenic citrus to canker disease.•Inhibiting the expression of CsFAO3 enhances the resistance of transgenic plants to canker disease.•CsFAO3 regulates leaf cuticular wax production through decarbonylation pathway. Long-chain fatty alcohol oxidase (FAO) plays an important role in plant responses to environmental stress in some species. However, there are no reports on whether FAO is involved in the response of citrus to biotic stress. In this study, a FAO gene CsFAO3 was cloned from Wanjincheng orange (Citrus sinensis Osbeck). Analysis of CsFAO3 expression revealed that it was specifically induced by the bacterial pathogen Xanthomonas citri pv. citri (Xcc) and exhibited tissue-specific expression, with the highest levels detected in the leaves. The promoter activity of CsFAO3 was also enhanced by Xcc induction. Overexpression of CsFAO3 increased the susceptibility of transgenic plants to citrus canker, whereas inhibition of CsFAO3 expression enhanced their resistance, demonstrating that CsFAO3 acts as a susceptibility gene for citrus canker. Furthermore, plants overexpressing CsFAO3 significantly increased cuticular wax content derived from the decarbonylation pathway, whereas those with inhibited CsFAO3 expression exhibited reduced levels of cuticular wax, alkanes, and secondary alcohols. Subcellular localization analysis indicated that CsFAO3 was localized in the endoplasmic reticulum. These results demonstrate that CsFAO3 is involved in the response of citrus to the Xcc pathogen by regulating the production of leaf culticular wax through the decarbonylation pathway.