TAL effectors and the predicted host targets of pomegranate bacterial blight pathogen Xanthomonas citri pv. punicae

The molecular mechanism of pomegranate susceptibility to bacterial blight, a serious threat to pomegranate production in India, is largely unknown. In the current study, we have used PacBio and Illumina sequencing of Xanthomonas citri pv. punicae (Xcp) strain 119 genome to identify tal genes and RNA-Seq analysis to identify putative host targets in the susceptible pomegranate variety Bhagwa challenged with Xcp119. Xcp119 genome encodes seven transcription activator-like effectors (TALEs), three of which are harbored by a plasmid. RVD-based phylogenetic analysis of TALEs of Xanthomonas citri pathovars indicate the TALEs of Xcp as evolutionarily and functionally close to Xanthomonas citri pv. malvacearum and Xanthomonas citri pv. glycines. Comparative RNA-Seq of Xcp and mock-inoculated leaf tissues revealed Xcp-induced pomegranate transcription modulation. The prediction of TALE binding elements (EBEs) in the promoters of up-regulated genes identified a set of TALE-targeted candidate genes in pomegranate-Xcp interaction. The predicted candidate susceptibility genes include two oxoglutarate-dependent dioxygenase gene, ethylene-responsive transcription factor and flavanone 3-hydroxylase-like gene, and the further characterization of these would enable blight resistance engineering in pomegranate.