CrRAP2.2 reprograms transcriptional networks associated with vascular cell wall remodeling and stress responses in Citrus

The Rap2.2 gene encodes a member of the APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) transcription factor family and plays an important role in plant growth, development, and responses to biotic and abiotic stresses. Previous studies have demonstrated that Rap2.2 contributes to resistance against Xylella fastidiosa in both Arabidopsis thaliana and Citrus species. Here, we further investigated the molecular mechanisms of Rap2.2 in Citrus that lead to X. fastidiosa resistance. Transgenic Citrus sinensis plants overexpressing CrRap2.2 from Citrus reticulata , a species naturally resistant to X. fastidiosa , were generated and subjected to transcriptomic and phenotypic analyses. RNA sequencing revealed that CrRap2.2 overexpression induces genes associated with cell wall remodeling, and both biotic and abiotic stress responses. Consistent with the transcriptomic data, histochemical analyses revealed enhanced lignin deposition in the xylem vessel elements of CrRap2.2 -overexpressing plants compared with wild-type controls. Collectively, these findings demonstrate that CrRAP2.2 reprograms defense-related transcriptional networks and promotes vascular cell wall reinforcement, establishing a mechanistic link between transcriptional regulation and xylem structural modification that likely underlies the contribution of this transcription factor to disease resistance.