Pathogen-Induced Expression of OsDHODH1 Suggests Positive Regulation of Basal Defense Against Xanthomonas oryzae pv. oryzae in Rice

Bacterial leaf blight (BLB), a vascular disease caused by Xanthomonas oryzae pv. oryzae (Xoo), induces a significant reduction in rice yield in severe epidemics. This study investigated the transcriptional regulation of the OsDHODH1 gene in rice cultivars exposed to the Xoo K3 isolate. The symptoms were monitored on a daily basis, and the lesion length of inoculated rice plants was scored 21 days post inoculation (dpi). The most resistant and the highly susceptible cultivars were used for gene expression analysis. The dihydroorotate dehydrogenase (DHODH) domain is shared by many proteins in different plant species, and in Arabidopsis, this protein is encoded by the AtPYD1 gene. To investigate the functional role of the OsDHODH1 gene under bacterial infection, we inoculated the Arabidopsis pyd1-2 knockout (atpyd1-2) plants, lacking the AtPYD1 gene (orthologous gene of the rice OsDHODH1), with Pseudomonas syringae pv. tomato (Pst) DC3000 vir, and the phenotypic response was scored 9 dpi. Results show that OsDHODH1 was upregulated in Tunnae, the most resistant rice cultivar but downregulated in IRAT112, the highly susceptible rice cultivar. In addition, Tunnae, Sipi and NERICA-L14 exhibited a durable resistance phenotype towards Xoo K3 isolate 21 dpi. Moreover, the expression of OsPR1a and OsPR10b (the rice pathogenesis inducible genes) was significantly upregulated in Tunnae, while being suppressed in IRAT112. Furthermore, the atpyd1-2 plants exhibited a high susceptibility towards Pst DC3000 vir. AtPR1 and AtPR2 (the Arabidopsis pathogenesis inducible genes) transcripts decreased in the atpyd1-2 plants compared to Col-0 (wild type) plants. Due to the above, OsDHODH1 and AtPYD1 are suggested to be involved in the basal adaptive response mechanisms towards bacterial pathogen resistance in plants.