Tulipa gesneriana and Lilium longiflorum PEBP Genes and Their Putative Roles in Flowering Time Control.

Floral induction in Tulipa gesneriana and Lilium longiflorum is triggered by contrasting temperature conditions, high and low temperature, respectively. In Arabidopsis, the floral integrator FLOWERING LOCUS T (FT), a member of the PEBP (phosphatidyl ethanolamine-binding protein) gene family, is a key player in flowering time control. In this study, one PEBP gene was identified and characterized in lily (LlFT) and three PEBP genes were isolated from tulip (TgFT1, TgFT2 and TgFT3). Overexpression of these genes in Arabidopsis thaliana resulted in an early flowering phenotype for LlFT and TgFT2, but a late flowering phenotype for TgFT1 and TgFT3. Overexpression of LlFT in L. longiflorum also resulted in an early flowering phenotype, confirming its proposed role as a flowering time-controlling gene. The tulip PEBP genes TgFT2 and TgFT3 have a similar expression pattern in tulip, but show opposite effects on the timing of flowering in Arabidopsis. Therefore, the difference between these two proteins was further investigated by interchanging amino acids thought to be important for the FT function. This resulted in the conversion of phenotypes in Arabidopsis upon overexpressing the substituted TgFT2 and TgFT3 genes, revealing the importance of these interchanged amino acid residues. Based on all obtained results, we hypothesize that LlFT is involved in creating meristem competence to flowering-related cues in lily, and TgFT2 is considered to act as a florigen involved in the floral induction in tulip. The function of TgFT3 remains unclear, but, based on our observations and phylogenetic analysis, we propose a bulb-specific function for this gene.

Combining comparative sequence and genomic data to ascertain phylogenetic relationships and explore the evolution of the large GDSL-lipase family in land plants.

The GDSL-lipase gene family is a very large subfamily within the supergene family of SGNH esterases, defined by the distinct GDSL amino acid motif and several highly conserved domains. Plants retain a large number of GDSL-lipases indicating that they have acquired important functions. Yet, in planta functions have been demonstrated for only a few GDSL-lipases from diverse species. Considering that orthologs often retain equivalent functions, we determined the phylogenetic relationships between GDSL-lipases from genome-sequenced species representing bryophytes, gymnosperms, monocots, and eudicots. An unrooted phylogenetic tree was constructed from the amino acid sequences of 604 GDSL-lipases from seven species. The topology of the tree depicts two major and one minor subfamily. This division is also supported by the unique gene structure of each subfamily. Because GDSL-lipase genes of all species are present in each of the three subfamilies, we conclude that the last common ancestor of the land plants already possessed at least one ancestral GDSL-lipase gene of each subfamily. Combined gene structure and synteny analyses revealed events of segmental duplications, gene transposition, and gene degeneration in the evolution of the GDSL-lipase gene family. Furthermore, these analyses showed that independent events of intron gain and loss also contributed to the extant repertoire of the GDSL-lipase gene family. Our findings suggest that underlying many of the intron losses was a spliceosomal-mediated mechanism followed by gene conversion. Sorting the phylogenetic relationships among the members of the GDSL-lipase gene family, as depicted by the tree and supported by synteny analyses, provides a framework for extrapolation of demonstrated functional data to GDSL-lipases, whose function is yet unknown. Furthermore, function(s) associated with specific lineage(s)-enriched branches may reveal correlations between acquired and/or lost functions and speciation.