The MADS-Domain Factors AGAMOUS-LIKE15 and AGAMOUS-LIKE18, along with SHORT VEGETATIVE PHASE and AGAMOUS-LIKE24, Are Necessary to Block Floral Gene Expression during the Vegetative Phase.

Donna E Fernandez,Sharyn E Perry,Benjamin J Adamczyk,Pamela K Hall,Chieh-Ting Wang,Yumei Zheng,Rajneesh Singhal

doi:10.1104/pp.114.242990

Donna E Fernandez, Sharyn E Perry + Show 5 more

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https://doi.org/10.1104/pp.114.242990

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Abstract

Multiple factors, including the MADS-domain proteins AGAMOUS-LIKE15 (AGL15) and AGL18, contribute to the regulation of the transition from vegetative to reproductive growth. AGL15 and AGL18 were previously shown to act redundantly as floral repressors and upstream of FLOWERING LOCUS T (FT) in Arabidopsis (Arabidopsis thaliana). A series of genetic and molecular experiments, primarily focused on AGL15, was performed to more clearly define their role. agl15 agl18 mutations fail to suppress ft mutations but show additive interactions with short vegetative phase (svp) mutations in ft and suppressor of constans1 (soc1) backgrounds. Chromatin immunoprecipitation analyses with AGL15-specific antibodies indicate that AGL15 binds directly to the FT locus at sites that partially overlap those bound by SVP and FLOWERING LOCUS C. In addition, expression of AGL15 in the phloem effectively restores wild-type flowering times in agl15 agl18 mutants. When agl15 agl18 mutations are combined with agl24 svp mutations, the plants show upward curling of rosette and cauline leaves, in addition to early flowering. The change in leaf morphology is associated with elevated levels of FT and ectopic expression of SEPALLATA3 (SEP3), leading to ectopic expression of floral genes. Leaf curling is suppressed by sep3 and ft mutations and enhanced by soc1 mutations. Thus, AGL15 and AGL18, along with SVP and AGL24, are necessary to block initiation of floral programs in vegetative organs.

Highlights

Appropriate timing of the shift from vegetative to reproductive growth is an important determinant of plant fitness
AGL15 and AGL18 contribute to flowering time regulation, but their effects can only be measured under non-inductive conditions
We reasoned that their contributions might be partially obscured by the contributions of SHORT VEGETATIVE PHASE (SVP) and members of the FLOWERING LOCUS C (FLC) clade, which have large quantitative effects on flowering time in Arabidopsis (reviewed in (Amasino, 2010)). svp mutations result in early flowering under both inductive and non-inductive conditions and are largely epistatic to flc and flm mutations, but show additive interactions with agl15 agl18 mutations (Adamczyk et al, 2007)

Summary

Introduction

Appropriate timing of the shift from vegetative to reproductive growth is an important determinant of plant fitness. The floral integrator FLOWERING LOCUS T (FT) is a major target of multiple flowering pathways, and the photoperiod pathway in particular. It is directly activated by CO (Samach et al, 2000). The changes in gene expression that accompany the floral transition must be rapid, robust, largely irreversible, and strictly controlled spatially. This is achieved through positive feedforward and negative feedback loops involving multiple regulatory factors (for recent review, see (Kaufmann et al, 2010))

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