Interaction of Polycomb-group proteins controlling flowering inArabidopsis

Abstract

In Arabidopsis, the EMBYRONIC FLOWER2 (EMF2), VERNALISATION2 (VRN2) and FERTILISATION INDEPENDENT ENDOSPERM2 (FIS2) genes encode related Polycomb-group (Pc-G)proteins. Their homologues in animals act together with other Pc-G proteins as part of a multimeric complex, Polycomb Repressive Complex 2 (PRC2), which functions as a histone methyltransferase. Despite similarities between the fis2 mutant phenotype and those of some other plant Pc-G members, it has remained unclear how the FIS2/EMF2/VRN2 class Pc-G genes interact with the others. We have identified a weak emf2 allele that reveals a novel phenotype with striking similarity to that of severe mutations in another Pc-G gene, CURLY LEAF (CLF), suggesting that the two genes may act in a common pathway. Consistent with this, we demonstrate that EMF2 and CLF interact genetically and that this reflects interaction of their protein products through two conserved motifs, the VEFS domain and the C5 domain. We show that the full function of CLF is masked by partial redundancy with a closely related gene, SWINGER(SWN), so that null clf mutants have a much less severe phenotype than emf2 mutants. Analysis in yeast further indicates a potential for the CLF and SWN proteins to interact with the other VEFS domain proteins VRN2 and FIS2. The functions of individual Pc-G members may therefore be broader than single mutant phenotypes reveal. We suggest that plants have Pc-G protein complexes similar to the Polycomb Repressive Complex2 (PRC2) of animals, but the duplication and subsequent diversification of components has given rise to different complexes with partially discrete functions.

Plant SET domain-containing proteins: Structure, function and regulation

“…In Arabidopsis, CLF controls leaf and flower morphology as well as flowering time through repression of the floral homeotic genes AGAMOUS (AG) and SHOOTMERISTEMLESS (STM) [51,52]. Its close relative, SWN, acts redundantly in mediating tri-methylation of histone H3K27 at both AG and STM loci [52,53]. MEA plays a role in maintaining its own imprinting during endosperm development and methylation of H3K27 is associated with MEA silencing during vegetative development and male gametogenesis [54][55][56].…”

Dynamic regulation of Polycomb group activity during plant development

“…While EMF-PRC2 represses important floral regulators, such as FLOWERING LOCUS T (FT), AGAMOUS (AG) and APETALA3 (AP3), the VRN-PRC2 complex promotes flowering after vernalization by silencing FLOWERING LOCUS C (FLC) [13][14]. However, EMF2 and VRN2 also have redundant functions, and the emf2 vrn2 double mutant, like the clf swn double mutant, produces mainly undifferentiated cells [13], indicating that both PRC2 complexes have a major role in ensuring differentiation and repressing stem cell genes.…”

“…However, in a recent report, this problem could be circumvented by fertilizing fie/FIE plants with pollen deficient for FIE and CYCLIN-DEPENDENT KINASE1;A [20]. Homozygous fie mutant seeds, like those of clf swn double mutants [13,[20][21], showed delayed germination and displayed a progressive loss of cell differentiation after germination, eventually resulting in callus growth. A similar de-differentiation phenotype had previously been described for a weak fie allele [13,[20][21].…”

“…Homozygous fie mutant seeds, like those of clf swn double mutants [13,[20][21], showed delayed germination and displayed a progressive loss of cell differentiation after germination, eventually resulting in callus growth. A similar de-differentiation phenotype had previously been described for a weak fie allele [13,[20][21]. These data show that PRC2 also plays an essential role in the embryo-to-seedling phase transition..…”

Developmental switches that hold the key to a revolution in crop biotechnology

“…The molecular mechanisms that underlie the developmental switch that directly transforms a somatic plant cell to an embryo are still elusive 9 . Several genes, such as WUSCHEL (WUS), SOMATIC EMBRYO RECEPTOR-LIKE KINASE 1 (SERK1), LEAFY COTYLEDON 1 (LEC1), LEC2 and BABY BOOM (BBM), can induce embryonic growth in plant somatic cells 10 , and Polycomb group proteins are also implicated in somatic embryogenesis 11 . However, it is uncertain whether these pathways for reprogramming of plant somatic cells towards embryogenesis are conserved among species.…”