Expression characteristics of CsESA1 in citrus and analysis of its interacting protein

Abstract The most damaging disease affecting citrus globally is Huanglongbing (HLB), primarily attributed to the infection by ‘Candidatus Liberibacter asiaticus’ (CaLas). Based on comparative transcriptome data, two cellulose synthase (CESA) genes responsive to CaLas infection induction were screened, and one gene cloned with higher differential expression level was selected and named CsCESA1. The yeast two-hybrid (Y2H) and Bimolecular Fluorescent Complementation (BiFC) experiments confirmed the interaction between CsCESA1 and citrus exopolysaccharide 2 (CsEPS2). Subcellular localization in tobacco indicated that both CsCESA1 and CsEPS2 proteins are primarily located in the nucleus and cytoplasm. RT-qPCR analysis indicated that the expression levels of CsCESA1 and CsEPS2 were associated with variety tolerance, tissue site, and symptom development. Furthermore, we employed the Virus-induced gene silencing (VIGS) system to generate CsCESA1 and CsEPS2 silencing plants. We established a stable transformation system mediated by Agrobacterium rhizogenes in citrus and obtained CsCESA1 and CsEPS2 silencing and overexpressing hairy roots. The analysis of hormone content and gene expression also showed that CsCESA1 and CsEPS2 are involved in transcriptional regulation of genes involved in systemic acquired resistance (SAR) response. In conclusion, our results suggested that CsCESA1 and CsEPS2 could serve as potential resistance genes for HLB disease, offering insights into the plant's defense mechanisms against HLB.