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Bacterial blight (BB) disease caused by Xanthomonas oryzae pv. oryzae (Xoo) is a costly disease in rice that threatens global rice production. The Xa21 gene is a broad spectrum BB-resistance gene that is extensively used for improving BB resistance in rice. The Xoo responsive gene,
Xoo-induced kinase 1 (XIK1), recently characterized in japonica rice, was also found to be involved in Xa21-mediated resistance. The current study investigated the differential expression of XIK1 in the BB-susceptible indica rice cultivar RD47 and its improved BB-resistant progenies BC3F3 (Xa21/Xa21) in various growth stages and during Xoo inoculation. The results showed that the expression of XIK1 was development-dependent and induced earlier in BB-resistant progenies BC3F3 than in the susceptible cultivar RD47 after Xoo inoculation. However, the expression levels of XIK1 substantially dropped after a peak of expression. Interestingly, the XIK1 expression tended to increase again in the succeeding hours post-inoculation in BC3F3 but not in RD47. Similar development and induction patterns were also observed when the expression of XIK1 and Xa21 was analyzed in the same runs in the BB-resistant BC3F3 under different growth stages and during Xoo inoculation. The findings suggested that XIK1 may also be involved in the Xa21-mediated resistance pathway of indica rice.