Mechanisms Of Floral Development Research Articles

A NAC transcription factor ZaNAC93 confers floral initiation, fruit development, and prickle formation in Zanthoxylum armatum

Zanthoxylum armatum is a dioecious prickly plant which developed apomictic reproduction. The increases in male flowers and prickle density in female plants lead to low yield and picking efficiency. However, little is known concerning the mechanisms of floral development and prickle formation. NAC is a well-known transcription factor that participates in multiple aspects of plant growth and development. Herein, we characterize the functions and regulatory mechanisms of candidate NACs controlling both traits in Z. armatum. A total of 159 ZaNACs were identified, and 16 of these were male-biased, represented by the NAP subfamily members ZaNAC93 and ZaNAC34, orthologs of AtNAC025 and AtNARS1/NAC2 respectively. Overexpression of ZaNAC93 in tomato led to modifications in flower and fruit development, including earlier flowering, increased numbers of lateral shoots and flowers, accelerated plant senescence, and reduced size and weight of fruits and seeds. In addition, the trichome density in leaves and inflorescences was dramatically reduced in ZaNAC93-OX lines. Overexpression of ZaNAC93 resulted in the up-/downregulation of genes associated with GA, ABA and JA signaling pathways, such as GAI, PYL and JAZ, as well as several TFs, including bZIP2, AGL11, FBP24 and MYB52. Yeast two-hybrid analysis revealed that ZaNAC93 protein could interact with AP1, GAI, bZIP2 and AGL11 in Z. armatum, which might contribute to floral induction, fruit growth, and trichome initiation. This work provides new insights into the molecular mechanisms of ZaNAC93 in reproductive development and prickle formation in Z. armatum.

Cloning and expression analysis of DtpsMADS1 gene from Doritaenopsis hybrid.

Plant MADS-box genes encode a family of highly conserved transcription factors which involved in many different developmental processes,including floral formation and flowering. To elucidate the molecular mechanisms of floral development in the monocotyledonous species Doritaenopsis hybrid,we isolated cDNA of a MADS-box gene from this plant by the method of 3' and 5' rapid amplification of cDNA ends using degenerate primers designed according to the MADS-box protein family conserved region from inflorescence rachis at flowering stage. The full length cDNA of this gene is 960 bp,with a 37 bp 5' UTR,an ORF of 753 bp and 185 bp 3' UTR encoding 245 putative amino acids. Sequence and phylogenetic analysis indicated a high degree of predicted protein sequence identity with those from other species. The gene belongs to the class of AP1 / FUL-like group of MADS-box genes and was termed as DtpsMADS1(accession No. JQ065097). Real-time quantitative PCR(qRT-PCR)results showed that DtpsMADS1 had obvious expression specificity in different organs;DtpsMADS1 had higher levels of expression in root and leaf at pre-flowering stage and post-flowering stage,meanwhile had lower levels of expression at seedling stage and full-blossom stage; The expression of DtpsMADS1 in inflorescence rachis showed the same tendency as root and leaf;However,only trace expression level was detected in flower organs. The results suggested that DtpsMADS1 could be involved in regulating the flowering process,not in floral morphogenesis.

Flowering Research in Taiwan

Flowering is an important and highly regulated process. Taiwanese researchers have contributed significantly to understanding flowering biology, including cell biology, cytogenetics and functional genomics, in rice, lily and especially orchids. In recognition of this effort, the PCP Editorial Board is publishing a special issue on flowering research in Taiwan. This issue contains seven articles on cutting-edge topics or reviews of flowering research carried out in Taiwan, focusing on research into orchids and lily. An anther consists of sporophytic tissues of three outer cell layers and an innermost layer, the tapetum. The tapetum has attracted the most attention. Tapetum cells are important in nurturing the maturing microspores, and their ablation leads to microspore death and thus male sterility (Hesse et al. 1993). In a review paper, M.-D. Huang et al. (pp. 1459–1466) provide information about current studies on the transcriptome of the anther sporophyte, including microarray and next-generation sequencing data. The authors illustrate a proposed gene regulation network of anther development in Arabidopsis using the most updated references. In addition, they point out potential studies worthwhile pursuing, including those of ‘secretomes’, antisense transcripts and small RNAs. Finally, they propose a model for exine precursor biosynthesis in tapetum cells and transport of these precursors from the tapetum cell to the microspore surface. With an estimated >25,000 species, orchids are the most species-rich of all angiosperm families (Leitch et al. 2009). They show a wide diversity of epiphytic and terrestrial growth forms and have successfully colonized almost every habitat on earth. The expansion of the orchid family probably took place in a comparatively short period as compared with that of most flowering plant families, which suggests exceptionally high speciation rates (Gill 1989). The production of orchids in the world has increased 12–18% every year since 2000. Taiwan is one of the world-renowned countries exporting orchids, because the climate is congenial to the growth of orchids and because of the rich resource of native species and advances in breeding techniques to produce more beautiful and elegant new varieties. Taiwan’s orchid industry has been recognized by the international community as prosperous in terms of sales volume, orchid plantation, orchid-growing technologies and financial resources. The most popular potted flowering plants are Phalaenopsis hybrids, and Oncidium are the top-traded cut flowers. Most, if not all, orchid flowers on the market are hybrids, such as Phalaenopsis spp., although most researchers use inbred lines such as Phalaenopsis equestris as materials for detailed studies. Fig. 1 illustrates several examples of orchid varieties, their mutants, disease and insect infection, as well as orchid production. In the second review paper of this issue, Hsiao et al. (pp. 1467–1486) provide an overview of the research activities in orchid biology and biotechnology, including the status of genomics, transformation technology, flowering regulation, molecular regulatory mechanisms of floral development, scent production and color presentation. The authors also point out the pros and cons of using orchids for genome research. Oncidium is a valuable floral genus of orchid. The yellow color is most often seen in the flower market. The largest flower structure is the labellum, also known as the lip (fig. 1E, p. 1533). Chang et al. (pp. 1532–1545) used 454 sequencing to perform deep sequencing of the Oncidium transcriptome using six organs. A value-added expressed sequence tag (EST) database, OncidiumOrchidGenomeBase (http://predictor.nchu. edu.tw/oogb/), was constructed and provides a foundation for molecular genetics and functional genomics for modifying the flowering quality and desirable agronomic traits of Oncidium. The authors also identified flowering time-associated genes, including photoreceptors and floral pathway integrators. Su et al. (pp. 1501–1514) performed transcriptome analysis of mixed vegetative and reproductive tissues of the moth orchid Phalaenopsis aphrodite and constructed the Orchidstra genome database (http://orchidstra.abrc.sinica.edu.tw) for searching and linking to corresponding Pfam, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Fu et al. (2011) prepared an EST database from 11 tissues collected from three orchid species, i.e. P. equestris, P. aphrodite and P. bellina, using both traditional and next-generation sequencing. This OrchidBase is freely available at http://lab.fhes.tn.edu.tw/est. Altogether, these three transcriptome databases consist of about 100,000 contigs from four orchid species and thus provide tremendous resources for orchid functional genomics studies as well as breeding application. Although the floral ABCDE model is generally thought to be ubiquitous in the core eudicots, studies of basal angiosperms,

The structure and expression of SEPALLATA-like genes in Asparagus species (Asparagaceae)

MADS-box genes encode transcriptional regulators that are critical for a number of developmental processes. In the MADS-box gene family, the SEPALLATA (SEP) gene subfamily plays an important role in controlling the development of floral organs in flowering plants. To understand the molecular mechanisms of floral development in Asparagus, we isolated and characterized several SEP-like genes from dioecious Asparagus officinalis and hermaphrodite A. virgatus: AOMADS1, AOMADS2, AOMADS3, and AVMADS1, AVMADS2, AVMADS3, respectively. Through alignment of the predicted amino acid sequences of various SEP-like genes, we defined three characteristic motifs in the C-terminal region of the genes: SEP motif I, SEP/AGL6 motif, and SEP motif II. Of the genes we isolated, AOMADS3 and AVMADS3 had lost the SEP motif II. Phylogenetic analysis revealed that AOMADS1, AOMADS2, AVMADS1, and AVMADS2 were closely related to SEP3 from Arabidopsis, whereas AOMADS3 and AVMADS3 were classified in different clade which is far related to SEP3 gene. Northern hybridization and RT-PCR showed that three SEP-like genes in A. officinalis were specifically expressed in the flower buds. In addition, PCR RFLP showed that there was no significant difference in the amount of transcripts of AOMADS1 and AOMADS2. These results suggest that AOMADS1 and AOMADS2 may be redundant genes. In contrast, the expression of AOMADS3 was weaker than that of AOMADS1 or AOMADS2, suggesting that the function of AOMADS3 may be different than that of AOMADS1 or AOMADS2.

AVAG2 is a putative D-class gene from an ornamental asparagus

Members of the AGAMOUS (AG) family of MADS-box genes play important roles in regulating the development of reproductive organs in flowering plants. To elucidate the molecular mechanisms of floral development in Asparagus virgatus, we isolated and characterized an Asparagus AG-homologue, AVAG2. AVAG2 contains an open reading frame that encodes a deduced protein with 234 amino acid residues. Phylogenetic analysis indicated that AVAG2 belongs to the D-lineage of the AG gene family. AVAG2 mRNA was detected in the flower, but not in vegetative organs. Moreover, in in situ hybridization experiments, AVAG2 signals were observed in the stamens and carpels during early flower development, and appeared in the ovule only at later developmental stages. This suggests that the AVAG2 gene is involved in ovule formation. Thus, our expression data support the phylogenetic analysis indicating that AVAG2 belongs to the D-class gene family.

Duplication and diversification in the APETALA1/FRUITFULL floral homeotic gene lineage: implications for the evolution of floral development.

Phylogenetic analyses of angiosperm MADS-box genes suggest that this gene family has undergone multiple duplication events followed by sequence divergence. To determine when such events have taken place and to understand the relationships of particular MADS-box gene lineages, we have identified APETALA1/FRUITFULL-like MADS-box genes from a variety of angiosperm species. Our phylogenetic analyses show two gene clades within the core eudicots, euAP1 (including Arabidopsis APETALA1 and Antirrhinum SQUAMOSA) and euFUL (including Arabidopsis FRUITFULL). Non-core eudicot species have only sequences similar to euFUL genes (FUL-like). The predicted protein products of euFUL and FUL-like genes share a conserved C-terminal motif. In contrast, predicted products of members of the euAP1 gene clade contain a different C terminus that includes an acidic transcription activation domain and a farnesylation signal. Sequence analyses indicate that the euAP1 amino acid motifs may have arisen via a translational frameshift from the euFUL/FUL-like motif. The euAP1 gene clade includes key regulators of floral development that have been implicated in the specification of perianth identity. However, the presence of euAP1 genes only in core eudicots suggests that there may have been changes in mechanisms of floral development that are correlated with the fixation of floral structure seen in this clade.