Arabidopsis Argonaute 2 Regulates Innate Immunity via miRNA393∗-Mediated Silencing of a Golgi-Localized SNARE Gene, MEMB12

Abstract

Summary Argonaute (AGO) proteins are critical components of RNA silencing pathways that bind small RNAs and mediate gene silencing at their target sites. We found that Arabidopsis AGO2 is highly induced by the bacterial pathogen Pseudomonas syringae pv. tomato (Pst). Further genetic analysis demonstrated that AGO2 functions in antibacterial immunity. One abundant species of AGO2-bound small RNAs is miR393b*, which targets a Golgi-localized SNARE gene MEMB12. Pst infection down-regulates MEMB12 in a miR393b*-dependent manner. Loss-of-function of MEMB12 but not SYP61, another intracellular SNARE, leads to increased exocytosis of an antimicrobial pathogenesis-related protein PR1. Overexpression of miR393b* resembles memb12 mutant in resistance responses. Thus, AGO2 functions in antibacterial immunity by binding miR393b* to modulate exocytosis of antimicrobial PR proteins via MEMB12. Since miR393 also contributes to antibacterial responses, miR393*/miR393 represent an example of a miRNA*/miRNA pair that functions in immunity through two distinct AGOs - miR393* through AGO2 while miR393 through AGO1.

mRNA Decay of Most Arabidopsis miRNA Targets Requires Slicer Activity of AGO1

“…2, A and B). Up-regulation of miR172 could be explained by stabilization through preferential loading into AGO2 (Zhang et al, 2011), whose levels are higher in ago1 null and slicer-deficient mutants (see below), probably due to defective repression of AGO2 by miR403 (Allen et al, 2005). Two miRNA*s (miR160* and miR173*) were clearly more abundant in ago1 null, but not in slicerdeficient mutants ( Fig.…”

“…2A). Although several miRNA*s are also loaded into AGO2 (Zhang et al, 2011), overaccumulation of AGO2 is not sufficient to explain the difference in miRNA* levels in null and slicer-deficient plants because AGO2 levels are similarly increased in both groups (see below). We conclude that the general trend of loss of miRNA in ago1 null mutants does not involve slicer activity.…”

Functional and Genetic Analysis Identify a Role for Arabidopsis ARGONAUTE5 in Antiviral RNA Silencing

“…However, some AGO proteins could have an indirect effect through association with endogenous microRNAs (Zhang et al, 2011;Seo et al, 2013). We therefore tested if the AGO2 and AGO5 proteins could bind PVX RNA.…”

RNAi in Plants: An Argonaute-Centered View

“…Arabidopsis AGO7 (also known as ZIP) specifically binds miR390 (Montgomery et al, 2008), which targets TAS3 transcripts (Bohmert et al, 1998;Morel et al, 2002;Vaucheret et al, 2004;Baumberger and Baulcombe, 2005;Qi et al, 2005;Zhang et al, 2006) ta-siRNAs vsiRNAs OsAGO1a Os02g45070 miRNAs Plant development, antiviral defense Os04g47870 miRNAs Plant development, antiviral defense (Wu et al, , 2015 (Takeda et al, 2008;Tucker et al, 2012;Brosseau and Moffett, 2015) vsiRNAs OsAGO5c Os03g58600 phasiRNAs Germ cell division (Nonomura et al, 2007;Komiya et al, 2014) AtAGO10 AT5G43810 miR165/166 SAM development, antiviral defense (Moussian et al, 1998;Lynn et al, 1999;Liu et al, 2009;Ji et al, 2011;Zhu et al, 2011;Garcia-Ruiz et al, 2015;Zhou et al, 2015) miR172 vsiRNAs (Harvey et al, 2011;Jaubert et al, 2011;Wang et al, 2011b;Zhang et al, 2011;Wei et al, 2012) vsiRNAs miR393* AtAGO3 AT1G31290 n.d. n.d. AtAGO7 AT1G69440 miR390 ta-siRNA biogenesis, phase transition, antiviral defense (Hunter et al, 2003;Adenot et al, 2006;Montgomery et al, 2008;Qu et al, 2008) OsAGO7 Os03g33650 miR390 ta-siRNA biogenesis, SAM development (Nagasaki et al, 2007) ZmAGO7 GRMZM5G892991 miR390 ta-siRNA biogenesis, leaf development (Douglas et al, 2010) AtAGO4 AT2G27040 hc-siRNAs DNA methylation, antibacterial immunity, defense against DNA viruses (Zilberman et al, 2003;Li et al, 2006;Pontes et al, 2006;…”