Systematic analyses of the MIR172 family members of Arabidopsis define their distinct roles in regulation of APETALA2 during floral transition

Abstract

MicroRNAs (miRNAs) play important roles in regulating flowering and reproduction of angiosperms. Mature miRNAs are encoded by multiple MIRNA genes that can differ in their spatiotemporal activities and their contributions to gene regulatory networks, but the functions of individual MIRNA genes are poorly defined. We functionally analyzed the activity of all 5 Arabidopsis thaliana MIR172 genes, which encode miR172 and promote the floral transition by inhibiting the accumulation of APETALA2 (AP2) and APETALA2-LIKE (AP2-LIKE) transcription factors (TFs). Through genome editing and detailed confocal microscopy, we show that the activity of miR172 at the shoot apex is encoded by 3 MIR172 genes, is critical for floral transition of the shoot meristem under noninductive photoperiods, and reduces accumulation of AP2 and TARGET OF EAT2 (TOE2), an AP2-LIKE TF, at the shoot meristem. Utilizing the genetic resources generated here, we show that the promotion of flowering by miR172 is enhanced by the MADS-domain TF FRUITFULL, which may facilitate long-term silencing of AP2-LIKE transcription, and that their activities are partially coordinated by the TF SQUAMOSA PROMOTER-BINDING-LIKE PROTEIN 15. Thus, we present a genetic framework for the depletion of AP2 and AP2-LIKE TFs at the shoot apex during floral transition and demonstrate that this plays a central role in floral induction.

Beyond the Genetic Pathways, Flowering Regulation Complexity in Arabidopsis thaliana

“…Indeed, SPL15 induces FUL and MIR172 . These three genes show a synergistic effect on flowering promotion [ 196 ]…”

MIR172d Is Required for Floral Organ Identity and Number in Tomato

“…The traditional approaches to study miRNA functions such as target mimicry and expression of a miRNA-resistant target mRNA are more suitable to study the generic function of a miRNA family rather than the function of specific miRNA family member. However, recently, the inactivation of specific MIR genes using CRISPR/Cas9 has proven useful to decipher the roles of individual miRNA family members [ 17 , 18 , 28 ]. Here, to identify the sly-miR172 members that are regulating flower development in tomato, several null and hypomorphic mutants were generated in SlMIR172c and SlMIR172d , which code for the predominant miR172 members in flower buds.…”

“…In Arabidopsis CRISPR-meditated mutagenesis of miR172 revealed its roles in phase transition, flowering time, and floral organ development [ 17 , 18 ]. In this study, we deciphered the functions of SlMIR172c and SlMIR172d in flower development.…”

“…Recently, a comprehensive functional analysis of MIR172 genes in Arabidopsis has shown that under non-inductive photoperiod, floral transition is dependent on the downregulation of TOE2 and AP2 mainly by MIR172d and to a lesser degree by MIR172a and MIR172b at the shoot apical meristem. Under inductive photoperiod, MIR172b , which is the main family member expressed in leaves, together with MIR172a promote flowering most probably by targeting AP2-LIKE transcription factors that suppress the expression of the florigen-encoding FLOWERING LOCUS T in leaves [ 13 , 15 , 16 , 17 , 18 ].…”

“…Recently, the use of clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated protein9 (Cas9) to mutate specific tomato MIR genes provided insights into their specific regulatory roles in development [ 28 ]. In contrast to the comprehensive understanding of miR172 and individual MIR172 gene functions in Arabidopsis [ 7 , 17 , 18 ], only two functional studies on tomato miR172 were published to date. These describe the ectopic expression of miR172 that resulted in the development of flowers with enlarged sepals showing sepal-to-petal transformation [ 29 , 30 ].…”