A Floricaula/Leafy gene homolog is preferentially expressed in developing female cones of the tropical pine Pinus caribaea var. caribaea

Abstract

In angiosperms, flower formation is controlled by meristem identity genes, one of which, FLORICAULA (FLO)/LEAFY (LFY), plays a central role. It is not known if the formation of reproductive organs of pre-angiosperm species is similarly regulated. Here, we report the cloning of a conifer (Pinus caribaea var. caribaea) FLO/LFY homolog, named PcLFY. This gene has a large C-terminal region of high similarity to angiosperm FLO/LFY orthologs and shorter regions of local similarity. In contrast to angiosperms, conifers have two divergent genes resembling LFY. Gymnosperm FLO/LFY proteins constitute a separate clade, that can be divided into two divergent groups. Phylogenetic analysis of deduced protein sequences has shown that PcLFY belongs to the LFY-like clade. Northern hybridization analysis has revealed that PcLFY is preferentially expressed in developing female cones but not in developing male cones. This expression pattern was confirmed by in situ hybridization and is consistent with the hypothesis of PcLFY being involved in the determination of the female cone identity. Additionally, mutant complementation experiments have shown that the expression of the PcLFY coding region, driven by the Arabidopsis LFY promoter, can confer the wild-type phenotype to lfy-26 transgenic mutants, suggesting that both gymnosperm and angiosperm LFY homologs share the same biological role.

The Ancestral Developmental Tool Kit of Land Plants

“…LEAFY has been identified primarily with the specification of floral meristems in angiosperms, since loss-of-function alleles result in a partial loss of floral meristem identity and gain-of-function alleles cause inflorescence meristems to differentiate as floral meristems (Coen et al 1990;Weigel et al 1992;Weigel and Nilsson 1995). Thus, in angiosperms, LEAFY is thought to regulate the transition from vegetative growth to reproductive growth by directly or indirectly regulating the transcription of the ABC floral organ identity genes in angiosperms, and its expression pattern in gymnosperms is consistent with a similar role in these taxa (Lee et al 1997;Mouradov et al 1998a;Parcy et al 1998;Busch et al 1999;Frohlich and Parker 2000;Shindo et al 2001;Dornelas and Rodriguez 2005). In a limited phylogenetic context, LEAFY also regulates complexity of leaf development in some legumes (Hofer et al 1997).…”

How Have Advances in Comparative Floral Development Influenced Our Understanding of Floral Evolution?

“…Species of Pinus, Welwitschia, and Ginkgo contain two LEAFY homologues, and early data suggested that the angiosperm sequence was most similar to a male-specific gymnosperm copy. However, more recent data have shown that both gymnosperm genes can have mixed expression patterns (Dornelas and Rodriguez 2005;Vázquez-Lobo et al 2007;Shindo et al 2010). Although further analysis has not supported the molecular genetic basis of the mostly male hypothesis, it is an important example of an early effort to use comparative developmental genetic data to inform evolutionary theory.…”

A link between LEAFY and B‐gene homologues in Welwitschia mirabilis sheds light on ancestral mechanisms prefiguring floral development

“…LFY ‐like genes are expressed in the developing GRS of all gymnosperms studied to date, consistent with a role for these genes in reproductive development (Mellerowicz et al ., ; Mouradov et al ., ; Shindo et al ., ; Carlsbecker et al ., ; Dornelas & Rodriguez, ; Guo et al ., ; Shiokawa et al ., ). A recent study in Norway spruce provides further support for a role of LFY‐like proteins in reproductive initiation: in the acrocona mutant, vegetative shoots can develop into female cones and this vegetative‐to‐reproductive transition correlates with an upregulation of LFY ‐like genes (Carlsbecker et al ., ).…”