Role In Flower Development Research Articles

The pineapple AcMADS1 promoter confers high level expression in tomato and Arabidopsis flowering and fruiting tissues, but AcMADS1 does not complement the tomato LeMADS-RIN (rin) mutant.

A previous EST study identified a MADS box transcription factor coding sequence, AcMADS1, that is strongly induced during non-climacteric pineapple fruit ripening. Phylogenetic analyses place the AcMADS1 protein in the same superclade as LeMADS-RIN, a master regulator of fruit ripening upstream of ethylene in climacteric tomato. LeMADS-RIN has been proposed to be a global ripening regulator shared among climacteric and non-climacteric species, although few functional homologs of LeMADS-RIN have been identified in non-climacteric species. AcMADS1 shares 67 % protein sequence similarity and a similar expression pattern in ripening fruits as LeMADS-RIN. However, in this study AcMADS1 was not able to complement the tomato rin mutant phenotype, indicating AcMADS1 may not be a functionally conserved homolog of LeMADS-RIN or has sufficiently diverged to be unable to act in the context of the tomato network of interacting proteins. The AcMADS1 promoter directed strong expression of the GUS reporter gene to fruits and developing floral organs in tomato and Arabidopsis thaliana, suggesting AcMADS1 may play a role in flower development as well as fruitlet ripening. The AcMADS1 promoter provides a useful molecular tool for directing transgene expression, particularly where up-regulation in developing flowers and fruits is desirable.

Down-regulation of AUXIN RESPONSE FACTORS 6 and 8 by microRNA 167 leads to floral development defects and female sterility in tomato.

Auxin regulates the expression of diverse genes that affect plant growth and development. This regulation requires AUXIN RESPONSE FACTORS (ARFs) that bind to the promoter regions of these genes. ARF6 and ARF8 in Arabidopsis thaliana are required to promote inflorescence stem elongation and late stages of petal, stamen, and gynoecium development. All seed plants studied thus far have ARF6 and ARF8 orthologues as well as the microRNA miR167, which targets ARF6 and ARF8. Whether these genes have broadly conserved roles in flower development is not known. To address this question, the effects of down-regulation of ARF6 and ARF8 were investigated through transgenic expression of Arabidopsis MIR167a in tomato, which diverged from Arabidopsis before the radiation of dicotyledonous plants approximately 90-112 million years ago. The transgenic tomato plants overexpressing MIR167a exhibited reductions in leaf size and internode length as well as shortened petals, stamens, and styles. More significantly, the transgenic plants were female-sterile as a result of failure of wild-type pollen to germinate on the stigma surface and/or to grow through the style. RNA-Seq analysis identified many genes with significantly altered expression patterns, including those encoding products with functions in 'transcription regulation', 'cell wall' and 'lipid metabolism' categories. Putative orthologues of a subset of these genes were also differentially expressed in Arabidopsis arf6 arf8 mutant flowers. These results thus suggest that ARF6 and ARF8 have conserved roles in controlling growth and development of vegetative and flower organs in dicots.

Phytoplasma Effector SAP54 Hijacks Plant Reproduction by Degrading MADS-box Proteins and Promotes Insect Colonization in a RAD23-Dependent Manner

Author SummaryParasites that colonize multiple hosts often coerce these hosts into improving their own survival and reproduction rates. However, how parasites do this is largely unknown. Phytoplasmas are bacterial plant parasites that require sap-feeding insect vectors—leafhoppers—for their propagation and dispersal. It has been known for a long time that phytoplasmas stimulate dramatic developmental changes in a broad range of plant species, such as the conversion of flowers into leaves known as phyllody and the proliferation of stems known as “witches' broom.” Here we report how and why phytoplasmas cause these dramatic developmental changes. We identified a phytoplasma virulence protein, SAP54, which transforms flowers into leaves and converts plants into more attractive hosts for the egg-laying and reproduction of their leafhopper vectors. We show that SAP54 exerts its effect by promoting the degradation of proteins that regulate important developmental processes in flowering plants. These proteins are highly conserved transcription factors of the MADS-box family, and reducing their activity through SAP54–mediated degradation curtails flower development, generating sterile plants. This degradation process requires RAD23, a protein that recruits the transcription factors to the protein degradation machinery. The resulting sterile plants, which form leaves in place of flowers, are more attractive to leafhoppers, arguably making phytoplasmas master manipulators of the parasite world.

Overexpression of a novel chrysanthemum SUPERMAN-like gene in tobacco affects lateral bud outgrowth and flower organ development

Previous studies have shown that the SUP genes play important roles in flower development and plant growth and morphogenesis. In this study, we isolated and characterized a SUPERMAN-like gene DgSZFP from chrysanthemum. DgSZFP contains one conserved Cys2/His2-type zinc finger motifs in the N-terminal region and an EAR-box in C-terminus. Its expression was significantly higher in nodes, flower buds, disc stamens, and petals than in the other tissues. Overexpression of DgSZFP in tobacco resulted in enhanced branching, reduced plant height, increased the width of petal tubes, produced the staminoid petals and petaloid stamens in flowers, and enhanced the seed weight and size. In addition, DgSZFP-overexpression tobacco plants accumulated high concentrations of cytokinin and chlorophyll. These results suggest that DgSZFP may be the candidate gene for regulating branching and floral organ development in chrysanthemum.

TcNPR3 from Theobroma cacao functions as a repressor of the pathogen defense response

BackgroundArabidopsis thaliana (Arabidopsis) NON-EXPRESSOR OF PR1 (NPR1) is a transcription coactivator that plays a central role in regulating the transcriptional response to plant pathogens. Developing flowers of homozygous npr3 mutants are dramatically more resistant to infection by the pathogenic bacterium Pseudomonas syringae, suggesting a role of NPR3 as a repressor of NPR1-mediated defense response with a novel role in flower development.ResultsWe report here the characterization of a putative NPR3 gene from the tropical tree species Theobroma cacao (TcNPR3). Like in Arabidopsis, TcNPR3 was constitutively expressed across a wide range of tissue types and developmental stages but with some differences in relative levels compared to Arabidopsis. To test the function of TcNPR3, we performed transgenic complementation analysis by introducing a constitutively expressing putative TcNPR3 transgene into an Arabidopsis npr3 mutant. TcNPR3 expressing Arabidopsis plants were partially restored to the WT pathogen phenotype (immature flowers susceptible to bacterial infection). To test TcNPR3 function directly in cacao tissues, a synthetic microRNA targeting TcNPR3 mRNA was transiently expressed in cacao leaves using an Agrobacterium-infiltration method. TcNPR3 knock down leaf tissues were dramatically more resistance to infection with Phytophthora capsici in a leaf bioassay, showing smaller lesion sizes and reduced pathogen replication.ConclusionsWe conclude that TcNPR3 functions similar to the Arabidopsis NPR3 gene in the regulation of the cacao defense response. Since TcNPR3 did not show a perfect complementation of the Arabidopsis NPR3 mutation, the possibility remains that other functions of TcNPR3 remain to be found. This novel knowledge can contribute to the breeding of resistant cacao varieties against pathogens through molecular markers based approaches or biotechnological strategies.

APETALA2 negatively regulates multiple floral organ identity genes inArabidopsisby recruiting the co-repressor TOPLESS and the histone deacetylase HDA19

The development and coordination of complex tissues in eukaryotes requires precise spatial control of fate-specifying genes. Although investigations of such control have traditionally focused on mechanisms of transcriptional activation, transcriptional repression has emerged as being equally important in the establishment of gene expression territories. In the angiosperm flower, specification of lateral organ fate relies on the spatial regulation of the ABC floral organ identity genes. Our understanding of how the boundaries of these expression domains are controlled is not complete. Here, we report that the A-class organ identity gene APETALA2 (AP2), which is known to repress the C-class gene AGAMOUS, also regulates the expression borders of the B-class genes APETALA3 and PISTILLATA, and the E-class gene SEPALLATA3. We show that AP2 represses its target genes by physically recruiting the co-repressor TOPLESS and the histone deacetylase HDA19. These results demonstrate that AP2 plays a broad role in flower development by controlling the expression domains of numerous floral organ identity genes.

Regulation of Floral Organ Identity in Arabidopsis by Ectopic Expression of OsMADS58

The ABCDE model has been described comprehensively to interpret the mechanism of floral organ development. In Arabidopsis , AGMAOUS was a well-studied class C gene encoding a transcription factor with MADS box, and its overexpression in Arabidopsis induced the transformation of sepals to carpels and petals to stamens. However, there is little knowledge about the function of OsMADS58, which was a homologue of AGMAOUS in rice. In our study, OsMADS58 driven by the UBIQUITIN promoter was ectopicly expressed in Arabidopsis. , and carpel-like sepals, incomplete petals and stamens instead of petals were found in different transgenic plants according to different OsMADS 58 mRNA expression levels. The phenotype of transgenic plant was similar to the AGMAOUS overexpression plant, suggesting that OsMADS 58 might play an important role in flower development like AGMAOUS and they keep conserved function during evolution.

Characterization of Osmads6-5, a null allele, reveals that OsMADS6 is a critical regulator for early flower development in rice (Oryza sativa L.)

AGL6-clade genes are a subfamily of MADS-box genes and preferentially expressed in floral organs. OsMADS6 and OsMADS17 are two AGL6-like genes in rice. OsMADS17 has been shown to play a minor role in floral development and appears to result from a duplication of OsMADS6. OsMADS6 was initially named as MFO1 for mosaic floral organs based on its moderate mutant phenotypes. So far, four moderate or weak mutant alleles of OsMADS6 have been described, providing valuable insights into its role in flower development. Here, we report a null allele of OsMADS6 (Osmads6-5), which exhibited a strong mutant phenotype in spikelet without affecting vegetative traits, causing all floral organs except lemma homeotically transformed into lemma-like organs (LLOs) as well as an indeterminate floral meristem, thus resulting in a mutant floret consisting of reiterating whorls of lemma and LLOs. In consistently, over-expression of OsMADS6 led to additional lodicule-, stamen- and carpel-like organs. Expression analysis showed that OsMADS6 controls the formation of the incipient primordia of lodicule, stamen and carpel via regulating the expression of class B, C and SEP-like MADS-box genes. Taken together, our results revealed that OsMADS6 acts as a critical regulator for early flower development in rice and provide novel insights into the molecular mechanism of OsMADS6.

Integrating two patterning processes in the flower

Spatial organ arrangement plays an important role in flower development. The position and the identity of floral organs is influenced by various processes, in particular the expression of MADS-box transcription factors for identity and dynamics of the plant hormone auxin for positioning. We are currently integrating patterning processes of MADS and auxin into our computational models, based on interactions that are known from experiments, in order to get insight in how these define the floral body plan. The resulting computational model will help to explore hypothetical interactions between the MADS and auxin regulation networks in floral organ patterning.

An APETALA1-like gene of soybean regulates flowering time and specifies floral organs

MADS-box proteins are key transcription factors involved in plant reproductive development. APETALA1 ( AP1) in Arabidopsis is a MIKC-type MADS-box gene and plays important roles in flower development. In this research, we isolated and characterized GmAP1, which encoded an AP1-like protein in soybean. GmAP1 contained eight exons and seven introns and was specifically expressed in the flower, especially in the sepal and petal. GmAP1 was a nucleus-localized transcription factor and displayed transactivation activity. It caused early flowering and alteration of floral organs when ectopically expressed in tobacco. To our knowledge, this is the first report characterizing an AP1-like gene from soybean.

Rice MADS6 Interacts with the Floral Homeotic Genes SUPERWOMAN1, MADS3, MADS58, MADS13, and DROOPING LEAF in Specifying Floral Organ Identities and Meristem Fate

AGAMOUS-LIKE6 (AGL6) genes play essential roles in flower development, but whether and how they work with floral organ identity genes remain less understood. Here, we describe interactions of the rice (Oryza sativa) AGL6 gene MADS6 with other rice floral homeotic genes in flower development. Genetic analyses revealed that MADS6 specifies the identity of the three inner whorls and floral meristem determinacy redundantly with SUPERWOMAN1/MADS16 (B-gene) or MADS3 (C-gene). MADS6 was shown to define carpel/ovule development and floral determinacy by interacting with MADS13 (D-gene) and control the palea and floral meristem identities together with the YABBY gene DROOPING LEAF. Expression analyses revealed that the transcript levels of six B-, C-, and E-class genes were reduced in mads6-1 at the early flower developmental stage, suggesting that MADS6 is a key regulator of early flower development. Moreover, MADS6 can directly bind to a putative regulatory motif on MADS58 (C-gene), and mads6-1 mads58 displayed phenotypes similar to that of mads6-1. These results suggest that MADS6 is a key player in specifying flower development via interacting with other floral homeotic genes in rice, thus providing new insights into the mechanism by which flower development is controlled.

Construction of a Full-Length cDNA Library of Gossypium hirsutum L. and Identification of Two MADS-Box Genes

Abstract A full-length normalized cDNA library for the flower development stages of short-season cotton (Gossypium hirsutum L.) (CCRI36) was constructed. A total of 3 421 clones were randomly selected for sequencing, with a total of 3 175 effective sequences obtained after removal of empty-carriers and low-quality sequences. Clustering the 3 175 high-quality expressed sequence tags (ESTs) resulted in a set of 2 906 non-redundant sequences comprised of 233 contigs and 2 673 singletons. Comparative analyses indicated that 913 (43.6%) of the unigenes had homologues with function-known genes or function-assumed genes in the National Center for Biotechnology Information. In addition, 763 (36.4%) of the unigenes were functionally classified using Gene Ontology hierarchy. Through EST alignment and the screening method, the full-length cDNA of two MADS-box genes viz., GhMADS11 and GhMADS12 were acquired. These genes may play a role in flower development. Phylogenetic analysis indicated that GhMADS11 and GhMADS12 had high homology and close evolutionary relationship with AGL2/SEP-type and Pi-type genes, respectively. The expression of both GhMADS11 and GhMADS12, genes was high in reproductive organs. In floral organs, GhMADS11 expression was high in petals (whorl2) and ovules, while GhMADS12 expression was high in petals (whorl2) and stamens (whorl3). Results show that the EST strategy based on a normalized cDNA library is an effective method for gene identification. The study provides more insights for future molecular research on the regulation mechanism of cotton flower development.

Functional analysis of SlEZ1 a tomato Enhancer of zeste (E(z)) gene demonstrates a role in flower development

The Enhancer of Zeste (E(z)) Polycomb group (PcG) proteins, which are encoded by a small gene family in Arabidopsis thaliana, have been shown to participate to the control of flowering and seed development. For the time being, little is known about the function of these proteins in other plants. In tomato E(z) proteins are encoded by at least two genes namely SlEZ1 and SlEZ2 while a third gene, SlEZ3, is likely to encode a truncated non-functional protein. The analysis of the corresponding mRNA demonstrates that these two genes are differentially regulated during plant and fruit development. We also show that SlEZ1 and SlEZ2 are targeted to the nuclei. These results together with protein sequence analysis makes it likely that both proteins are functional E(z) proteins. The characterisation of SlEZ1 RNAi lines suggests that although there might be some functional redundancy between SlEZ1 and SlEZ2 in most plant organs, the former protein is likely to play specific function in flower development.

Characterization and expression analysis of PhalLFY, a homologue in Phalaenopsis of FLORICAULA/LEAFY genes

FLORICAULA/LEAFY (FLO/LFY) homologues are floral meristem identifying genes and play a key role in flower development among diverse species. Phalaenopsis is one of the world's most popular flowers. To understand the molecular mechanism of the reproduction process, PhalLFY, a FLO/LFY homologue gene was cloned from Phalaenopsis hybrida (cv.wedding promenade) and its expression pattern was analysed during vegetative as well as reproductive development. The full cDNA of PhalLFY was 1655 bp in length with an open reading frame (ORF) of 1422 bp encoding 424 amino acids. The analysis based on amino acid sequence alignment showed that PhalLFY shared a high degree of similarity to LFY-like (68%) from Anacamptis, LFY-like (61%) from Hyacinthus, RFL (60%) from Oryza sativa and LFY (54%) from Arabidopsis. A transient expression assay using PhalLFY/GFP fusion protein showed that PhalLFY was nucleus-localized protein. Semi-quantitative RT-PCR analysis and in situ hybridization results showed that PhalLFY was expressed both in the vegetative organs as well as the reproductive organs. Its transcripts accumulated at higher levels in the stem during the transition from vegetative to reproductive growth, especially in the inflorescence meristems, floral meristems, floral primordia and all floral organs during the floral developmental stage of P. hybrida. Moreover, PhalLFY transcript was lower in the young phase than in the mature phase. These results suggest that PhalLFY is a FLO/LFY homologue probably involved in the control of Phalaenopsis reproductive development.

Interactions among Proteins of Floral MADS-Box Genes in Basal Eudicots: Implications for Evolution of the Regulatory Network for Flower Development

Floral MADS-box genes encode transcription factors that play critical roles in the development and evolution of the flower. Proteins of floral MADS-box genes regulate the expression of their downstream genes by forming various homodimers/heterodimers and quaternary complexes. Interactions among proteins of floral MADS-box genes have been documented in several model species, yet the information accumulated so far is still not sufficient to draw a general picture of the evolution of the interactions. We have characterized 28 putative floral MADS-box genes from three representative basal eudicots (i.e., Euptelea pleiospermum, Akebia trifoliata, and Pachysandra terminalis) and investigated the protein-protein interactions (PPIs) among the proteins encoded by these genes using yeast two-hybrid assays. We found that, although the PPIs in basal eudicots are largely consistent with those in core eudicots and monocots, there are lineage-specific features that have not been observed elsewhere. We also reconstructed the evolutionary histories of the PPIs among members of seven MADS-box gene lineages (i.e., AP1, AP3, PI, AG, STK, AGL2, and AGL9) in angiosperms. We revealed that the PPIs were extremely conserved in nine (or 32.1%) of the 28 possible combinations, whereas considerable variations existed in seven (25.0%) of them; in the remaining 12 (or 42.9%) combinations, however, no interaction was observed. Notably, most of the PPIs required for the formation of quaternary complexes, as suggested by the "quartet model," were highly conserved. This suggested that the evolutionarily conservative PPIs may have played critical roles in the establishment of the basic structure (or architecture) of the flower and experienced coevolution to maintain their functions. The evolutionarily variable PPIs, however, seem to have played subsidiary roles in flower development and have contributed to the variation in floral traits.

Cloning and Characterization of MADS-box Gene in Oil Palm

Oil palm has emerged as one of the most important source of oils and fats. The mechanism of floral organs development in this plant is still at its infancy. We describe here the cloning and characterization of a MADS-box gene in oil palm (Elaeis guineensis Jacq.) named EMADS1. It belongs to the AGAMOUS-like2 family of MADS-box gene which plays critical role in flower development as defined by the ABCDE model. EMADS1 was ubiquitously expressed in the immature male and female flower buds and its expression pattern was similar to EgAGL2 and EgMADS8 of oil palm. The EMADS1 transcript also accumulated in embryos of developing seeds. These results suggested that EMADS1 is likely to function at the initial stages of flowering in determination of the inflorescence and the identity of the flower whorls and also embryo development in seeds.

Recent advances in ethylene research

Ethylene regulates many aspects of the plant life cycle, including seed germination, root initiation, flower development, fruit ripening, senescence, and responses to biotic and abiotic stresses. It thus plays a key role in responses to the environment that have a direct bearing on a plant's fitness for adaptation and reproduction. In recent years, there have been major advances in our understanding of the molecular mechanisms regulating ethylene synthesis and action. Screening for mutants of the triple response phenotype of etiolated Arabidopsis seedlings, together with map-based cloning and candidate gene characterization of natural mutants from other plant species, has led to the identification of many new genes for ethylene biosynthesis, signal transduction, and response pathways. The simple chemical nature of ethylene contrasts with its regulatory complexity. This is illustrated by the multiplicity of genes encoding the key ethylene biosynthesis enzymes 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase, multiple ethylene receptors and signal transduction components, and the complexity of regulatory steps involving signalling relays and control of mRNA and protein synthesis and turnover. In addition, there are extensive interactions with other hormones. This review integrates knowledge from the model plant Arabidopsis and other plant species and focuses on key aspects of recent research on regulatory networks controlling ethylene synthesis and its role in flower development and fruit ripening.

The LEAFY Floral Regulators in Angiosperms: Conserved Proteins with Diverse Roles

Genetic analyses in model angiosperms have shown that the LEAFY/FLORICAULA transcription factor plays a central role in flower development. In Arabidopsis, LEAFY (LFY) triggers the development of floral meristems and controls their patterning through the activation of floral organ identity genes. Several recent reports enlighten the structure and function of this conserved protein but also illustrate the variety of roles it plays in different angiosperms.

Isolation and functional analysis of the CjNdly gene, a homolog in Cryptomeria japonica of FLORICAULA/LEAFY genes

We report the isolation and characterization of CjNdly, a homolog in Japanese cedar (Cryptomeria japonica D. Don) of the FLORICAULA/LEAFY (FLO/LFY) genes. We determined the entire nucleotide sequence of CjNdly, including short 5'- and 3'-untranslated regions. The deduced amino acid sequence was similar to those of the products of the FLO/LFY genes from other species. The nucleotide sequence showed the closest homology to that of the NEEDLY gene in Pinus radiata D. Don. Although no proline-rich region has been reported previously in homologous gene products from gymnosperms, we found such a region at the amino-terminal end of the deduced amino acid sequence encoded by CjNdly. We detected the expression of CjNdly in both reproductive and vegetative tissues and organs of C. japonica. Heterologous expression of CjNdly in transgenic tobacco plants induced precocious flowering of regenerating shoots on agar-solidified medium and flowers with an abnormal phenotype, namely, petal-like stamens. Our findings suggest that the CjNdly gene may have important roles in flower development in Japanese cedar, resembling those of its angiosperm homologs.

RsLFY, a LEAFY homologue gene in radish (Raphanus sativus), is continuously expressed in vegetative, reproductive and seed development

The floral meristem identity gene LEAFY (LFY) in Arabidopsis plays a key role in flower development. We isolated two LFY-like genes from radish, designated RsLFY1 and RsLFY2. Comparison of genomic and cDNA sequences revealed that the number and positions of introns are precisely conserved in RsLFY1, RsLFY2 and LFY. Using RsLFY1 full- length cDNA as a probe, genomic DNA blot hybridization analysis detected two hybridizing fragments under high stringency, suggesting that there are two RsLFY loci within radish genome. Both genes were expressed during vegetative growth, reproductive growth, flower development and seed development. RsLFY1 was expressed slightly in leaf primordia and strongly in early floral meristem. It was expressed successively in primordia of sepals, petals, stamens, gynoecium, ovule integument and mature seeds. These results suggest that RsLFY1 plays a similar role to LFY in floral initiation and the developmental stages of floral organs, and that it also may regulate radish seed development, unlike LFY.