MicroRNAs against bacterial pathogens
A number of miRNAs involved in the regulation of rice immunity against
bacterial pathogens have been identified. Of these, five miRNAs have
been shown to modulate bacterial blight (BB) disease caused byXanthomonas oryzae pv. oryzae (Xoo ) and one miRNA
has been shown to positively regulate bacterial foot rot disease caused
by Dickeya zeae . Of the miRNAs regulating BB, Osa-miR159bacts in positive manner, while the others are involved in negative
regulation. The Osa-miR159b enhances resistance to BB by
repressing its target gene OsGAMYB, with concomitant effects in
terms of reduced nitrogen concentration and significantly repressed
activity of the GA signaling pathway (Jia et al. 2020).
The Osa-miR167 has also been shown to be involved in rice
immunity (Li et al. 2010; Yao, Withers & He 2013). TheOsa-miR167d abates the rice immunity upon Xanthomonas
oryzae pv. oryzae (Xoo) infection by suppressing the
target gene OsWD40-174, which function in maintaining the
downregulation of OsKNOX gene during leaf development (Jiaet al. 2020). Downregulation of KNOX hinders lignin biosynthesis
(Mele, Ori, Sato & Hake 2003). Transgenic plants overexpressingOsa-miR164a enhances susceptibility to Xoo by virtue of
the reduced accumulation of OsNAC60 (Jia et al. 2020). The
role of miR164a/OsNAC60 regulatory module in blast resistance has
been discussed earlier in this review. The Osa-miR169o represents
the coordinated regulation of the crosstalk between BB and N-use
efficiency in rice. Overexpression of the miR169o enhances N use
efficiency and susceptibility to BB by suppressing the Nuclear
factor Y-A (NF-YA ) which lead to significant reduction in the
transcript abundance of several defense related genes includingPR10b, PR1b, PR10a and PAL (Yu et al. 2018). TheOsa-miR156 negatively regulates rice immunity against the
bacterial blight (Liu et al. 2019). Transgenic plants
overexpressing the target gene IPA1 (Ideal Plant
Architecture 1 ) under the control of pathogen-inducible promoter ofOsHEN1 has been shown to enhance both disease resistance and
yield in rice.
More recently, Osa-miR396f was shown to play a positive role in
conferring resistance against bacterial foot rot disease caused byDickeya zeae. Overexpression of Osa-miR396f in the
susceptible rice variety Nipponbare showed enhanced immunity to D.
zeae by suppressing target gene OsGRFs (Growth-Regulating
Factors ). However, the molecular mechanism underpinning the immunity
against bacterial foot root mounted by OsGRFs remains to be
elusive (Li et al. 2019b).