| Summary: | Bacterial leaf blight (BLB), a vascular disease caused by <i>Xanthomonas</i><i>oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>), induces a significant reduction in rice yield in severe epidemics. This study investigated the transcriptional regulation of the <i>OsDHODH1</i> gene in rice cultivars exposed to the <i>Xoo</i> 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 <i>Arabidopsis</i>, this protein is encoded by the <i>AtPYD1</i> gene. To investigate the functional role of the <i>OsDHODH1</i> gene under bacterial infection, we inoculated the <i>Arabidopsis</i><i>pyd1-2</i> knockout (<i>atpyd1-2)</i> plants, lacking the <i>AtPYD1</i> gene (orthologous gene of the rice <i>OsDHODH1</i>), with <i>Pseudomonas</i><i>syringae</i> pv. <i>tomato</i> (<i>Pst</i>) DC3000 <i>vir</i>, and the phenotypic response was scored 9 dpi. Results show that <i>OsDHODH1</i> 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 <i>Xoo</i> K3 isolate 21 dpi. Moreover, the expression of <i>OsPR1a</i> and <i>OsPR10b</i> (the rice pathogenesis inducible genes) was significantly upregulated in Tunnae, while being suppressed in IRAT112. Furthermore, the <i>atpyd1-2</i> plants exhibited a high susceptibility towards <i>Pst</i> DC3000 <i>vir</i>. <i>AtPR1</i> and <i>AtPR2</i> (the <i>Arabidopsis</i> pathogenesis inducible genes) transcripts decreased in the <i>atpyd1-2</i> plants compared to Col-0 (wild type) plants. Due to the above, <i>OsDHODH1</i> and <i>AtPYD1</i> are suggested to be involved in the basal adaptive response mechanisms towards bacterial pathogen resistance in plants.
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