Perianth Development in the Basal Monocot Triglochin Maritima (Juncaginaceae)

Basal monocots exhibit considerable variation in inflorescence and floral structure. In some cases, such as Triglochin maritima, it is not clear whether the lateral and terminal structures of the inflorescence are flowers or pseudanthia, or where the limits between flowers and inflorescence lie. To address these questions, morphological studies were carried out, and the results show that in T. maritima both terminal and lateral structures are flowers, not pseudanthia. The terminal flower of T. maritima develops from the apical inflorescence meristem, suggesting that the apical meristem identity changes from inflorescence to flower during inflorescence development. In addition, distal flowers of T. maritima are reduced, and there is no distinct flower-subtending bract; instead, the perianth develops unidirectionally, resulting in an abaxial-median bract-like tepa! and bilaterally symmetrical flowers, similar to those of other basal monocots, such as Aponogeton and Acarus. It is possible that the leaf primordium changes its positional homology from flower-subtending bract to tepal. Therefore, in some basal angiosperms with abbreviated development of lateral flowers the demarcation of the flower vs. the inflorescence is ontogenetically ambiguous. In situ hybridization experiments show that a putative ortholog of the B-class gene APETALA3/DEFICIENS is expressed in developing stamens and carpels, and may also be expressed in the shoot axis of the very young inflorescence. This expression pattern seems to be consistent with the gradual transition between inflorescence and flower that was observed morphologically

Floral gene resources from basal angiosperms for comparative genomics research

BACKGROUND: The Floral Genome Project was initiated to bridge the genomic gap between the most broadly studied plant model systems. Arabidopsis and rice, although now completely sequenced and under intensive comparative genomic investigation, are separated by at least 125 million years of evolutionary time, and cannot in isolation provide a comprehensive perspective on structural and functional aspects of flowering plant genome dynamics. Here we discuss new genomic resources available to the scientific community, comprising cDNA libraries and Expressed Sequence Tag (EST) sequences for a suite of phylogenetically basal angiosperms specifically selected to bridge the evolutionary gaps between model plants and provide insights into gene content and genome structure in the earliest flowering plants. RESULTS: Random sequencing of cDNAs from representatives of phylogenetically important eudicot, non-grass monocot, and gymnosperm lineages has so far (as of 12/1/04) generated 70,514 ESTs and 48,170 assembled unigenes. Efficient sorting of EST sequences into putative gene families based on whole Arabidopsis/rice proteome comparison has permitted ready identification of cDNA clones for finished sequencing. Preliminarily, (i) proportions of functional categories among sequenced floral genes seem representative of the entire Arabidopsis transcriptome, (ii) many known floral gene homologues have been captured, and (iii) phylogenetic analyses of ESTs are providing new insights into the process of gene family evolution in relation to the origin and diversification of the angiosperms. CONCLUSION: Initial comparisons illustrate the utility of the EST data sets toward discovery of the basic floral transcriptome. These first findings also afford the opportunity to address a number of conspicuous evolutionary genomic questions, including reproductive organ transcriptome overlap between angiosperms and gymnosperms, genome-wide duplication history, lineage-specific gene duplication and functional divergence, and analyses of adaptive molecular evolution. Since not all genes in the floral transcriptome will be associated with flowering, these EST resources will also be of interest to plant scientists working on other functions, such as photosynthesis, signal transduction, and metabolic pathways