Systematic analysis and functional verification of citrus ascorbate peroxidases reveal that CsAPX01 and CsAPX02 negatively regulate citrus bacterial canker through the hydrogen peroxide regulation.

Ascorbate peroxidases (APXs) are antioxidant enzymes that play vital roles in redox homeostasis in plants. Citrus is susceptible to infection by Xanthomonas citri subsp. citri (Xcc), resulting in citrus bacterial canker (CBC). The present study used bioinformatic and expression analyses to investigate the APX family in Citrus sinensis. Bioinformatic research revealed the chromosomal locations, phylogeny, gene structure, promoter elements, functional domains, conserved motifs, and most likely physicochemical properties of the sequences. Six APXs clustered in three groups were identified, with each protein containing a single peroxidase domain. The promoter regions contained a variety of transcription factor-binding and hormone-response components. Xcc infection induced different CsAPX01 and CsAPX02 expressions in the CBC-susceptible Wanjincheng and CBC-resistant Kumquat varieties. Subcellular localization and transient expression showed that CsAPX01 and CsAPX02 were expressed in the cytoplasm and nucleus and had hydrogen peroxide (HO)-scavenging activity. Virus-induced gene silencing (VIGS) of CsAPX01 and CsAPX02 resulted in strong resistance to CBC and HO bursts without effects on the plant phenotype. The current study focused on investigating and characterizing the citrus APX family. It was found that CsAPX01 and CsAPX02 exacerbated CBC by altering the balance of HO. These findings emphasize the importance of APXs in enhancing plant resistance to pathogens.