Differential expression of Xoo-induced kinase 1 (XIK1), a Xanthomonas oryzae pv. oryzae responsive gene, in bacterial blight-susceptible and Xa21-mediated resistant indica rice cultivars

Abstract

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.