Comparative microRNA profiling reveals microRNAs involved in rice resistant response to bacterial blight

Bacterial blight (BB), which is caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most destructive bacterial diseases of rice (Oryza sativa L.). During plant defense responses, microRNAs (miRNAs) play important roles in regulating disease resistance. However, the functions of miRNAs in the interaction between rice and Xoo remain relatively uncharacterized. In this study, we compared the miRNA profiles of the BB resistant rice introgression line F329 and its susceptible recurrent parent Huang-Hua-Zhan (HHZ) at multiple time points after inoculation with Xoo. A total of 538 known and 312 novel miRNAs were identified, among which only 17 and 26 were responsive to Xoo infection in F329 and HHZ, respectively. Compared with the expression levels in HHZ, 37 up-regulated and 53 down-regulated miRNAs were detected in F329. The predicted target genes for the miRNAs differentially expressed between F329 and HHZ were revealed to be associated with flavonoid synthesis, the reactive oxygen species regulatory pathway, plant hormone signal transduction, defense responses, and growth and development. Additionally, the patterns of interactions between osa-miR390-3p, novel_miR_104, novel_miR_238, osa-miR166k-5p, osa-miR529b, and osa-miR167h-3p and their target genes were further validated by quantitative real-time PCR. Furthermore, we overexpressed osa-miR167h-3p in transgenic plants and proved that this miRNA positively regulates the resistance of rice to BB. These results provide novel information regarding the miRNA-based molecular mechanisms underlying the disease resistance of rice. The data presented herein may be useful for engineering rice BB resistance via miRNAs.