The WRKY transcription factor CsWRKY55 positively regulates citrus bacterial canker resistance in Citrus sinensis

•CsWRKY55 encodes a nucleus-localized Xcc-inducible WRKY transcription factor.•Overexpressing CsWRKY55 confers the citrus plant CBC resistance while silence of CsWRKY55 causes CBC susceptibility.•CsWRKY55 regulates the expression of genes involved in phytohormone biosynthesis and signaling. Citrus bacterial canker (CBC) is an infection caused by Xanthomonas citri subsp. citri (Xcc), adversely affecting citrus production. Plant-specific WRKY transcription factors positively regulate the expression of genes involved in defense against pathogens. However, the role of CsWRKY55 in CBC resistance remains unknown. CsWRKY55 was found to be upregulated in the CBC-resistant Kumquat citrus variety but not in the sensitive Wanjincheng variety, as shown by qRT-PCR, indicating its involvement in Xcc infection. Furthermore, CsWRKY55 was observed to be localized in the nucleus. Transient overexpression of CsWRKY55 markedly increased resistance to CBC, while virus-induced gene silencing enhanced susceptibility. Biochemical analyses demonstrated that CsWRKY55 silencing reduced the production of salicylic acid (SA) and increased the synthesis of jasmonic acid (JA) and abscisic acid (ABA). In summary, the findings of the study indicate that CsWRKY55 is a positive regulator that enhances resistance against CBC by altering the biosynthesis and signaling of JA, SA, and ABA. These results suggest that modulation of CsWRKY55 could be beneficial in the production of CBC-resistant citrus.