MicroRNA172 regulates growth under low nitrogen conditions in Arabidopsis thaliana.

miR172 and its target genes TOE1 and TOE2 regulate low nitrogen (LN) dependent root elongation growth in Arabidopsis thaliana. Overexpression of miR172 suppresses LN mediated PR elongation. Reduced responses of miR172 overexpression lines and toe1-2;toe2-1 mutants to LN are associated with impaired nitrate assimilation, suggesting a role of the miR172-TOE1/TOE2 module in regulating plant growth under LN conditions. MicroRNAs (miRNAs), a class of small non-coding regulatory RNAs, play important roles in various aspects of plant growth and stress responses, including nutrient deficiency. The availability of nitrogen (N), an essential mineral for plant growth, affects the expression of several miRNAs. However, the function of miRNAs in modulating root responses under low nitrogen (LN) condition remains elusive. Here we report that LN differentially regulates miR172 expression levels, which modulate plant response. Overexpression of miR172 (miR172OE) reduced the plant response to LN-mediated PR elongation, whereas miR172-target mimic (MIM172) lines exhibited enhanced LN-dependent PR elongation in Arabidopsis thaliana (Arabidopsis). Cellular analysis at the root tip revealed that miR172OE plants exhibited a reduced response to LN-mediated root cell elongation and meristem zone (MZ) inhibition, whereas MIM172 plants maintained LN-responsive regulation of these cellular parameters comparable to wild-type. Consistent with these findings, LN-mediated suppression of chlorophyll levels was compromised in miR172OE plants. Analysis of miR172 target genes suggests that among the known targets [SCHLAFMUTZE (SMZ), SCHNARCHZAPFEN (SNZ), APETALA2 (AP2), TARGET OF EAT1 (TOE1), TOE2, and TOE3], TOE1 and TOE2 are involved in LN-dependent elongation of PR through modulation of cellular activities at the root tip. The toe1-2;toe2-1 double mutants showed reduced response to PR elongation and compromised cell elongation under LN condition. Further, chlorate sensitivity assay data suggest that reduced response of miR172OE lines and toe1-2;toe2-1 double mutants under LN condition is associated with a reduced nitrate assimilation pathway. Together, our findings suggest the role of miR172 and its targets TOE1 and TOE2 in regulating nitrogen-responsive growth and the nitrate assimilation pathway.