Identification and expression analysis of OsmiR1861k in rice leaves in response to Xanthomonas oryzae pv. oryzae

OsmiR1861k was predicted to be inducible by Xanthomonas oryzae pv. oryzae (Xoo) in resistant rice leaves by using a computational approach based on transcription data. The existence of many known pathogen-related cis-elements in the promoter region of OsmiR1861k further supported the prediction. A stem-loop real-time RT-PCR analysis validated that OsmiR1861k was significantly upregulated in resistant genotype SH5 in comparison with the less-resistant genotype 8411 at 3 and 5 days after inoculation with Xoo strain Zhe173. Two target genes of OsmiR1861k were downregulated in SH5 at the same time after inoculation with Zhe173. Among 3 precursors with an identical mature miRNA, only pre-OsmiR1861k was significantly induced by Zhe173 in 2 genotypes. The expression of OsmiR1861k increased significantly in 4 other resistant genotypes to different extents after Zhe173 attack, but not in the susceptible genotypes. Resistant genotypes generally had higher constitutive levels of OsmiR1861k than did the susceptible. OsmiR1861k in SH5 leaves was also induced by 6 other Xoo strains. Together, these results suggested that OsmiR1861k might have a role in wide spectrum resistance.