The miR172 target TOE3 represses AGAMOUS expression during Arabidopsis floral patterning

Abstract

microRNA172 (miR172) regulates phase transition and floral patterning in Arabidopsis by repressing targets that encode the APETALA2 (AP2) and AP2-like transcription factors. The miR172-mediated repression of the AP2 gene restricts AGAMOUS (AG) expression. In addition, most miR172 targets, including AP2, redundantly act as floral repressors, and the overexpression of the target genes causes delayed flowering. However, how miR172 targets other than AP2 regulate both of the developmental processes remains unclear. Here, we demonstrate that miR172-mediated repression of the TARGET OF EAT 3 (TOE3) gene is critical for floral patterning in Arabidopsis. Transgenic plants that overexpress a miR172-resistant TOE3 gene (rTOE3-ox) exhibit indeterminate flowers with numerous stamens and carpelloid organs, which is consistent with previous observations in transgenic plants that overexpress a miR172-resistant AP2 gene. TOE3 binds to the second intron of the AG gene. Accordingly, AG expression is significantly reduced in rTOE3-ox plants. TOE3 also interacts with AP2 in the nucleus. Given the major role of AP2 in floral patterning, miR172 likely regulates TOE3 in floral patterning, at least in part via AP2. In addition, a miR156 target SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3 directly activates TOE3 expression, revealing a novel signaling interaction between miR156 and miR172 in floral patterning.

Keywords: -glucuronidase; AG; AGAMOUS; AP2; APETALA2; Arabidopsis; CaMV; ChIP; FLOWERING LOCUS T; FT; Floral patterning; GUSβ; MS; Murashige & Skoog; SOC1; SPL3; SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3; SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1; TARGET OF EAT 3; TOE3; cauliflower mosaic virus; chromatin immunoprecipitation; miR172; microRNA172; qRT-PCR; quantitative real-time RT-PCR.