<Emphasis Type="Italic">OsMADS22</Emphasis>, an <Emphasis Type="Italic">STMADS11</Emphasis>-like MADS-box gene of rice,is expressed in non-vegetative tissues and its ectopic expression induces spikelet meristem indeterminacy

We report the cDNA sequence and gene expression patterns of OsMADS22, a novel member of the STMADS11-like family of MADS-box genes, from rice. In contrast to previously reported STMADS11-like genes, whose expression is detected in vegetative tissues, OsMADS22 is mainly expressed during embryogenesis and flower development. In situ hybridization analysis revealed that OsMADS22 expression is localized in the L1 layer of embryos and in developing stamen primordia. Ectopic expression of OsMADS22 in transgenic rice plants resulted in aberrant floral morphogenesis, characterized by a disorganized palea, an elongated glume, and a two-floret spikelet. The results are discussed in terms of rice spikelet development and a novel non-vegetative role for a STMADS11-like gene.     

<Emphasis Type="Italic">SQUA</Emphasis>-like genes in the orchid <Emphasis Type="Italic">Phalaenopsis</Emphasis> are expressed in both vegetative and reproductive tissues

The SQUA family (AP1/FUL family) of MADS-box genes plays an important role in the transition from the vegetative to the reproductive development of angiosperms, and its origin might be concurrent with fixation of floral structure in angiosperms. Here, we isolated two Phalaenopsis MADS-box genes designated ORAP11 and ORAP13, both of which belong to the monocot FUL-like clade of the SQUA family. RT-PCR showed that both genes are strongly expressed in the floral bud, and also detected in the vegetative organs. During later stages, ORAP11 was only detected in the column, but ORAP13 signal was absent from all of the floral organs. In-situ hybridization experiments detected both genes in the tips and margins of developing petals and lips, the developing column, and ovule. Over-expression of both genes in tobacco induced early flowering and changed plant architecture. Our results suggest that in Phalaenopsis, both genes might share partly redundant activities and play important roles in the process of floral transition and morphological architecture. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Characterization of the <Emphasis Type="Italic">Selaginella remotifolia</Emphasis> MADS-box gene

Recent progress in plant molecular genetics has revealed that floral organ development is regulated by several homeotic selector genes, most of which belong to the MADS-box gene family. Here we report on SrMADS1, a MIKC^c-type MADS-box gene from Selaginella, a spikemoss belonging to the lycophytes. SrMADS1 phylogenetically forms a monophyletic clade with genes of the LAMB2 group, which are MIKC^c genes of the clubmoss Lycopodium, and is expressed in whole sporophytic tissues except roots and rhizophores. Our results and the previous report on Lycopodium MIKC^c genes suggest that the ancestral MIKC^c gene of primitive dichotomous plants in the early Devonian was involved in the development of basic sporophytic tissues such as shoot, stem, and sporangium. Electronic Publication     

The modified ABC model explains the development of the petaloid perianth of <Emphasis Type="Italic">Agapanthus praecox</Emphasis> ssp. <Emphasis Type="Italic">orientalis</Emphasis> (Agapanthaceae) flowers

The class B genes, which belong to the MADS-box gene family, play important roles in regulating the development of petals and stamens in flowering plants. To understand the molecular mechanisms of floral development in Agapanthus praecox ssp. orientalis (Agapanthaceae), we isolated and characterized the homologs of the Antirrhinum majus genes GLOBOSA and DEFICIENS in this plant. These were designated as ApGLO and ApDEF, respectively. ApGLO and ApDEF contain open reading frames that encode deduced protein with 210 and 214 amino acid residues, respectively. Phylogenetic analysis indicated that ApGLO and ApDEF belong to the monocot class B gene family. In situ hybridization experiments revealed that hybridization signals of ApGLO and ApDEF were observed in whorl 1 as well as in whorls 2 and 3. Moreover, the flowers of transgenic Arabidopsis plants that ectopically expressed ApGLO formed petal-like organs in whorl 1. These observations indicate that the flower developmental mechanism of Agapanthus follows the modified ABC model.     

Characterization of <Emphasis Type="Italic">SpAPETALA3</Emphasis> and <Emphasis Type="Italic">SpPISTILLATA</Emphasis>, B class floral identity genes in <Emphasis Type="Italic">Spinacia oleracea</Emphasis>, and their relationship to sexual dimorphism

Floral organ identity B class genes are generally recognized as being required for development of petals and stamens in angiosperm flowers. Spinach flowers are distinguished in their complete absence of petals in both sexes, and the absence of a developed stamen whorl in female flowers. As such, we hypothesized that differential expression of B class floral identity genes is integral to the sexual dimorphism in spinach flowers. We isolated two spinach orthologs of Arabidopsis B class genes by 3 and 5 RACE. Homology assignments were tested by comparisons of percent amino acid identities, searches for diagnostic consensus amino acid residues, conserved motifs, and phylogenetic groupings. In situ hybridization studies demonstrate that both spinach B class genes are expressed throughout the male floral meristem in early stages, and continue to be expressed in sepal primordia in reduced amounts at later stages of development. They are also highly expressed in the third whorl primordia when they arise and continue to be expressed in these tissues through the development of mature anthers. In contrast, neither gene can be detected in any stage in female flowers by in situ analyses, although northern blot experiments indicate low levels of SpAP3 within the inflorescence. The early, strong expressions of both B class floral identity genes in male floral primordia and their absence in female flowers demonstrate that B class gene expression precedes the origination of third whorl primordia (stamen) in males and is associated with the establishment of sexual floral dimorphism as it initiates in the first (sepal) whorl. These observations suggest that regulation of B class floral identity genes has a role in the development of sexual dimorphism and dioecy in spinach rather than being a secondary result of organ abortion.Electronic Supplementary Material Supplementary material is available for this article at Edited by G. Jürgens     

<Emphasis Type="Italic">MIR166</Emphasis>/<Emphasis Type="Italic">165</Emphasis> genes exhibit dynamic expression patterns in regulating shoot apical meristem and floral development in <Emphasis Type="Italic">Arabidopsis</Emphasis>

The miR166/165 group and its target genes regulate diverse aspects of plant development, including apical and lateral meristem formation, leaf polarity, and vascular development. We demonstrate here that MIR166/165 genes are dynamically controlled in regulating shoot apical meristem (SAM) and floral development in parallel to the WUSCHEL (WUS)-CLAVATA (CLV) pathway. Although miR166 and miR165 cleave same target mRNAs, individual MIR166/165 genes exhibit distinct expression domains in different plant tissues. The MIR166/165 expression is also temporarily regulated. Consistent with the dynamic expression patterns, an array of alterations in SAM activities and floral architectures was observed in the miR166/165-overproducing plants. In addition, when a MIR166a-overexpressing mutant was genetically crossed with mutants defective in the WUS-CLV pathway, the resultant crosses exhibited additive phenotypic effects, suggesting that the miR166/165-mediated signal exerts its role via a distinct signaling pathway.     

Flower form alteration by genetic transformation with the class B MADS-box genes of <Emphasis Type="Italic">Agapanthus</Emphasis><Emphasis Type="Italic">praecox</Emphasis> spp. <Emphasis Type="Italic">orientalis</Emphasis> in transgenic dicot and monocot plants

The class B genes, which belong to the MADS-box gene family, play important roles in regulating petal and stamen development in flowering plants. These genes exist in two different types termed DEF- and GLO-like genes, and the B-function is provided by heterodimers of a DEF- and a GLO-like gene product. In the present study, dicot (tobacco and lettuce) and monocot (Tricyrtis hirta) plants were transformed with the GLO-like gene of Agapanthus praecox ssp. orientalis ApGLO alone or in combination with the DEF-like gene of the same plant ApDEF. In two out of 10 transgenic tobacco plants containing ApGLO, sepals partially converted into petaloid organs. For lettuce, ray florets of four out of nine transgenic plants containing ApGLO also developed additional petaloid organs. In two out of five transgenic T. hirta plants containing both ApGLO and ApDEF, organs developed in whorl 4 showed noticeable morphological alteration: they were much longer compared with carpels of non-transgenic plants, and had purple spots overall on the surface as filaments of non-transgenic plants. No morphological alterations were observed in vegetative organs between transgenic and non-transgenic plants for all the three species. The results obtained in the present study indicate a possibility of molecular breeding for flower form alteration by genetic transformation with the class B MADS-box gene(s) of heterologous plant species.     

Expression pattern of two paralogs of the <Emphasis Type="Italic">PI</Emphasis>/<Emphasis Type="Italic">GLO</Emphasis>-like locus during <Emphasis Type="Italic">Orchis italica</Emphasis> (Orchidaceae,Orchidinae) flower development

The class B MADS-box genes belong to two distinct functional groups: the AP3/DEF-like and the PI/GLO-like sub-families. In orchids, AP3/DEF-like genes are present in four copies, each with a different role in floral organ formation, which is described in the “orchid code” model. Interestingly, the orchid PI/GLO-like genes are present in two copies in Orchidinae, whereas they are described as single copy in the other orchid lineages. The two PI/GLO-like paralogs have site-specific different selective constraints; in addition, they show relaxation of purifying selection when compared to the single-copy lineages. In this study, we present a comparative analysis of the expression patterns of the two PI/GLO-like paralogs, OrcPI and OrcPI2, in floral tissues of Orchis italica in different developmental stages using real-time PCR. The two genes show similar expression profiles in the tissue examined, with differences detectable between immature and mature inflorescence. In all cases, OrcPI2 is expressed at a higher level than OrcPI. Real-time PCR results reveal that the co-expression of the two duplicated loci could have a fully or partially redundant function. The possible evolutionary fate of OrcPI and OrcPI2 is discussed as well as their involvement in ovary development.     

Functional analysis of an <Emphasis Type="Italic">APETALA1</Emphasis>-like MADS box gene from <Emphasis Type="Italic">Eustoma grandiflorum</Emphasis> in regulating floral transition and formation

An Eustoma grandiflorum APETALA1 (EgAP1) gene showing high homology to the SQUA subfamily of MADS-box genes was isolated and characterized. EgAP1, containing a conserved euAP1 motif at the C-terminus, showed high sequence identity to Antirrhinum majus SQUAMOSA in the SQUA subfamily. EgAP1 mRNA was detected in the leaf and expressed significantly higher in young flower buds than in mature flower buds. In flowers, EgAP1 mRNA was strongly detected in sepal, weakly detected in petal and was absent in stamen and carpel. Transgenic Arabidopsis plants ectopically expressing EgAP1 flowered early and produced terminal flowers. In addition, the conversion of petals into stamen-like structures was also observed in 35S::EgAP1 flowers. 35S::EgAP1 was able to complement the ap1 flower defects by restoring the defect for sepal formation and significantly increasing second whorl petal production in Arabidopsis ap1 mutant plants. These results revealed that EgAP1 is the APETALA1 homolog in E. grandiflorum and that the function of EgAP1 is involved in floral induction and flower formation.     

Overexpression of <Emphasis Type="Italic">AP1-</Emphasis>like genes from <Emphasis Type="Italic">Asteraceae</Emphasis> induces early-flowering in transgenic <Emphasis Type="Italic">Chrysanthemum</Emphasis> plants

Chrysanthemum is one of the most important commercial cut flowers in the world. Early-flowering cultivars are required to produce quality chrysanthemum flowers with a lower cost of production. To shorten the vegetative growth phase of chrysanthemum, three AP1-like genes from Asteraceae were constitutively overexpressed in 80 independent transgenic chrysanthemum lines. All lines were characterized by PCR and RT-PCR and demonstrated that overexpression of compositae AP1-homologs in transgenic chrysanthemum under long-day conditions had no effect on plant development compared to non-transgenic controls. Conversely, under short-day conditions, transgenic plants commenced bud initiation 2 wk earlier than non-transgenic chrysanthemum plants. Subsequently, transgenic chrysanthemum flowers showed color earlier and resulted in full opening of inflorescences 3 wk prior to non-transgenic control plants. These results open new possibilities for genetic improvement and breeding of chrysanthemum cultivars.     

Characterization of <Emphasis Type="Italic">HoMADS 1</Emphasis> and its induction by plant hormones during <Emphasis Type="Italic">in vitro</Emphasis> ovule development in <Emphasis Type="Italic">Hyacinthus orientalis</Emphasis> L.

To understand the molecular mechanism of ovule development, a MADS box gene,HoMADS 1, has been isolated from the ovule tissues of Hyacinthus. Sequence comparison showed that HoMADS 1 is highly homologous to both class C and D genes. Furthermore, phylogenetic analysis suggests that HoMADS 1 is most likely a class D MADS box gene. RNA hybridization revealed that HoMADS 1 was exclusively expressed in the ovules. Over-expressing HoMADS 1 in transgenic Arabidopsis plants produced ectopic carpelloid structures, including ovules, indicating that HoMADS 1 is involved in the determination of carpel and ovule identities. Interestingly, during in vitro flowering, no HoMADS 1 mRNA was detected in the floral tissues at high level hormones in the media. However, HoMADS 1 mRNA accumulated in the floral tissues when the regenerated flowers were transferred to the media containing low level hormones which could induce in vitro ovule formation. Our data suggest that the induction of HoMADS 1 by plant hormones may play important roles during ovule initiation and development in the regenerated flower. Whether HoMADS 1 expression is also regulated by cytokinin and auxin during ovule development in planta remains to be investigated.