MAF2 Is Regulated by Temperature-Dependent Splicing and Represses Flowering at Low Temperatures in Parallel with FLM.

Chiara A Airoldi,Mary Mckay,Brendan Davies,Mohammed Bendahmane

doi:10.1371/journal.pone.0126516

Abstract

Plants enter their reproductive phase when the environmental conditions are favourable for the successful production of progeny. The transition from vegetative to reproductive phase is influenced by several environmental factors including ambient temperature. In the model plant Arabidopsis thaliana, SHORT VEGETATIVE PHASE (SVP) is critical for this pathway; svp mutants cannot modify their flowering time in response to ambient temperature. SVP encodes a MADS-box transcription factor that directly represses genes that promote flowering. SVP binds DNA in complexes with other MADS-box transcription factors, including FLOWERING LOCUS M (FLM), which acts with SVP to repress the floral transition at low temperatures. Small temperature changes post-transcriptionally regulate FLM through temperature-dependent alternative splicing (TD-AS). As ambient temperature increases, the predominant FLM splice isoform shifts to encode a protein incapable of exerting a repressive effect on flowering. Here we characterize a closely related MADS-box transcription factor, MADS AFFECTING FLOWERING2 (MAF2), which has independently evolved TD-AS. At low temperatures the most abundant MAF2 splice variant encodes a protein that interacts with SVP to repress flowering. At increased temperature the relative abundance of splice isoforms shifts in favour of an intron-retaining variant that introduces a premature termination codon. We show that this isoform encodes a protein that cannot interact with SVP or repress flowering. At lower temperatures MAF2 and SVP repress flowering in parallel with FLM and SVP, providing an additional input to sense ambient temperature for the control of flowering.

Highlights

The timing of the vegetative to reproductive phase transition in plants is influenced by many environmental stimuli
Since MADS AFFECTING FLOWERING2 (MAF2) is capable of interacting with SHORT VEGETATIVE PHASE (SVP) [12], we investigated the significance of SVP for MAF2 function by analysing flowering time in single and double mutants
Comparisons of flowering time in WT, maf2, svp, and svp maf2 backgrounds revealed that the early flowering phenotype seen in svp is not significantly enhanced in the svp maf2 double mutant (Fig 1A), suggesting that MAF2 and SVP are in the same pathway and that the MAF2-SVP interaction is required for the repression of flowering by MAF2

Summary

Introduction

The timing of the vegetative to reproductive phase transition in plants is influenced by many environmental stimuli. Perception and integration of a range of environmental signals maximises reproductive success and species fitness. Initiation of the reproductive phase is regulated by environmental variables, such as day-length and temperature, in addition to endogenous. Low Temperature Repression of Flowering by MAF2 signals such as plant age [1] [2]. In Arabidopsis thaliana these diverse inputs are integrated by regulating the expression of a limited set of genes including FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS (SOC1). FT and SOC1 are known as floral pathway integrators [3], because several pathways converge on these activators of flowering to translate endogenous and exogenous signals into the decision to flower

Methods

Results

Conclusion