Potentiation of host defense through sRNA packaged in OMVs of Xanthomonas oryzae pv. oryzicola

Bacterial outer membrane vesicles (OMVs)-packaged delivery of noncoding small RNAs (sRNAs) can function as novel mediators of interspecies communication. However, the role in the interaction between phytopathogenic bacteria and their host plants is unclear. In this study, we characterized differentially packaged sRNAs in Xanthomonas oryzae pv. oryzicola (Xoc) BLS256 OMVs using RNA-Seq, and we selected the most abundant sRNA Xosr001 for further study based on its essential role in the induction of stomatal immunity in rice. Xoc loads Xosr001 into OMVs, which are transferred specifically into the mechanical tissues of rice leaves. We uncovered that OMVs-mediated Xosr001 inhibitors attenuated OsJMT1 transcripts in vivo and reduced the endogenous MeJA contents in rice leaves. Stomatal conductance was measured to show that ΔXosr001 mutant weakened the ability of stomatal re-opening on rice leaves after spray inoculation. Most notably, the transgenic rice lines OsJMT1-HA-OE exhibited attenuated stomatal immunity and disease susceptibility after ΔXosr001 infection compared with Xoc infection. These results define that Xosr001 packaged in Xoc OMVs highlights a smart molecular mechanism to activate stomatal immunity in rice.