MicroRNA172 controls inflorescence meristem size through regulation of APETALA2 in Arabidopsis

The APETALA2 (AP2) transcription factor regulates flower development, floral transition and shoot apical meristem (SAM) maintenance in Arabidopsis. AP2 is also regulated at the post-transcriptional level by microRNA172 (miR172), but the contribution of this to SAM maintenance is poorly understood. We generated transgenic plants carrying a form of AP2 that is resistant to miR172 (rAP2) or carrying a wild-type AP2 susceptible to miR172. Phenotypic and genetic analyses were performed on these lines and mir172 mutants to study the role of AP2 regulation by miR172 on meristem size and the rate of flower production. We found that rAP2 enlarges the inflorescence meristem by increasing cell size and cell number. Misexpression of rAP2 from heterologous promoters showed that AP2 acts in the central zone (CZ) and organizing center (OC) to increase SAM size. Furthermore, we found that AP2 is negatively regulated by AUXIN RESPONSE FACTOR 3 (ARF3). However, genetic analyses indicated that ARF3 also influences SAM size and flower production rate independently of AP2. The study identifies miR172/AP2 as a regulatory module controlling inflorescence meristem size and suggests that transcriptional regulation of AP2 by ARF3 fine-tunes SAM size determination.

Automated summary

The AP2 transcription factor is important for flower development, floral transition, and shoot apical meristem maintenance in Arabidopsis. It is regulated by microRNA172 (miR172) at the post-transcriptional level, but its contribution to shoot apical meristem maintenance is not well understood. In this study, transgenic plants with a miR172-resistant form of AP2 were generated to investigate its role in meristem size and flower production. The results show that miR172-resistant AP2 increases the size of the inflorescence meristem by enlarging cells and increasing cell number. Additionally, the study also identified a negative regulation of AP2 by AUXIN RESPONSE FACTOR 3 (ARF3). However, genetic analysis suggests that ARF3 independently influences shoot apical meristem size and flower production rate. This study highlights the importance of miR172/AP2 regulation in controlling meristem size and suggests that transcriptional regulation of AP2 by ARF3 fine-tunes shoot apical meristem size determination.