A variant of LEAFY reveals its capacity to stimulate meristem development by inducing RAX1

Abstract

SUMMARYIn indeterminate inflorescences, floral meristems develop on the flanks of the shoot apical meristem, at positions determined by auxin maxima. The floral identity of these meristems is conferred by a handful of genes called floral meristem identity genes, among which the LEAFY (LFY) transcription factor plays a prominent role. However, the molecular mechanism controlling the early emergence of floral meristems remains unknown. A body of evidence indicates that LFY may contribute to this developmental shift, but a direct effect of LFY on meristem emergence has not been demonstrated. We have generated a LFY allele with reduced floral function and revealed its ability to stimulate axillary meristem growth. This role is barely detectable in the lfy single mutant but becomes obvious in several double mutant backgrounds and plants ectopically expressing LFY. We show that this role requires the ability of LFY to bind DNA, and is mediated by direct induction of REGULATOR OF AXILLARY MERISTEMS1 (RAX1) by LFY. We propose that this function unifies the diverse roles described for LFY in multiple angiosperm species, ranging from monocot inflorescence identity to legume leaf development, and that it probably pre-dates the origin of angiosperms.

The WRKY Transcription Factor WRKY71/EXB1 Controls Shoot Branching by Transcriptionally Regulating RAX Genes in Arabidopsis

“…Up to now, few transcription factors have been reported to directly regulate RAX genes. LEAFY was reported to bind to the promoter region of RAX1 directly (Chahtane et al, 2013). Our data suggested that RAX genes are very likely regulated by EXB1 directly for the following reasons.…”

The Stem Cell Niche in Leaf Axils Is Established by Auxin and Cytokinin in Arabidopsis

“…This discrepancy has recently been reconciled by the finding that auxin promotes the expression of LEAFY (LFY), a key regulator of the floral transition, and that LFY feeds back to the auxin pathway (Li et al, 2013;Yamaguchi et al, 2013). LFY further activates the expression of RAX1 to promote inflorescence branching (Chahtane et al, 2013).…”

Molecular Dynamics Simulations of Ternary Complexes: Comparisons of LEAFY Protein Binding to Different DNA Motifs

“…Interestingly, two separate mutation studies using the same amino acid substitutions in the dimerization interface obtained opposite results. 11,14 In our study, the amino acid sequences of the dimerization interfaces are not identical in the AtLFY and PpLFY1 proteins. Nevertheless, except for different interaction modes at position 312 in helix α3, the two LFY proteins have similar DNAbinding specificity (see Table 1).…”

“…In 2013, based on the crystallographic data of 2008, Chahtane et al generated a LFY allele that has an altered dimerization interface in vivo. 14 This study broke new ground by revealing a novel role for LFY in enabling meristem outgrowth. They confirmed the importance of LFY monomer− monomer contacts and tested the effect of the mutations at the dimerization interface on LFY DNA-binding specificity.…”