Plant small RNAs:
- siRNA: ta-siRNAs(trans-acting siRNAs); phasiRNAs (secondary phased siRNAs); nat-siRNAs (natural antisense transcripts-derived siRNAs); hc-siRNAs (heterochromatic siRNAs); lsiRNAs (long siRNAs)
miRNA/siRNA in plants involved in microbe interaction (pathogen and symbiosis):
- miRNA393 in Arabidopsis silence Auxin receptor to activate Pathogen-associated molecular pattern triggered immunity
- miR863-3p silence both negative and positive regulators of plant immunity and ﬁne-tune the timing and amplitude of immune responses
- 22-nt miRNAs cleave target mRNAs to produce phasiRNAs, which targeted NLRs. Upon pathogen infection, both these miRNA and siRNA are downregulated, which lead to upregulation of NLRs.
(nat-miR6019 in tobacco; miR482 and miR2118 in tomato; miR472 in Arabidopsis)
(some miRNA triggered siRNA also target PRRs: miR6021, miR6022, and miR6023 target a tomato gene encoding a transmembrane receptor-like protein)
Summary: expression of some NLR and PRR genes is tightly suppressed by 22 nt miRNAs and secondary phasiRNAs in absence of pathogens to avoid autoimmune responses and to save energy for plant growth.
- Some NLR proteins such as SNC1 can repress transcription of miRNA and phasiRNA as well indicating a regulatory circuit
- hc-siRNA-mediated transcriptional silencing ((RdDM)) regulate the NLRs expression.
the miRNAs reported involved in symbiosis
miR160 :plays a crucial role in maintaining the auxin/cytokinin balance during soybean nodule inception and maturation.
(Nizampatnam et al., 2015)
miR167 : acts upstreamofNIN,NSP1,NF-YA1,NF-YA2,andENOD40andpositively regulates nodule formation by inhibiting GmARF8a and GmARF8b expression (Auxin-mediated organogenesis)
(Wang et al., 2015).