Ectopic expression of an orchid (Oncidium Gower Ramsey) AGL6-like gene promotes flowering by activating flowering time genes in Arabidopsis thaliana

An AP1/AGL9 group of MADS box gene, OMADS1, with extensive homology to the Arabidopsis AGAMOUS-like 6 gene (AGL6) was characterized from orchid (Oncidium Gower Ramsey). OMADS1 mRNA was detected in apical meristem and in the lip and carpel of flower. Yeast two-hybrid analysis indicated that OMADS1 is able to strongly interact with OMADS3, a TM6-like protein that was involved in flower formation and floral initiation in orchid. Transgenic Arabidopsis and tobacco ectopically expressed OMADS1 showed similar novel phenotypes by significantly reducing plant size, flowering extremely early, and losing inflorescence indeterminacy. In addition, homeotic conversion of sepals into carpel-like structures and petals into staminoid structures were also observed in flowers of 35S::OMADS1 Arabidopsis. This result indicated that OMADS1 was involved in floral formation and initiation in transgenic plants. Further analysis indicated that the expression of flowering time genes FT, SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) and flower meristem identity genes LEAFY (LFY), APETALA1 (AP1) was significantly up-regulated in 35S::OMADS1 transgenic Arabidopsis plants. Furthermore, ectopic expression of OMADS1 rescued late-flowering phenotype in gi-1, co-3 but not for ft-1 and fwa-1 mutants. These results supported that ectopic expression of OMADS1 influenced flower transition and formation by acting as an activator for FT and SOC1 in Arabidopsis.     

Two lily SEPALLATA-like genes cause different effects on floral formation and floral transition in Arabidopsis

Two AGL2-like MADS-box genes, Lily MADS Box Gene (LMADS) 3 and LMADS4, with extensive homology of LMADS3 to the Arabidopsis SEPALLATA3 were characterized from the lily (Lilium longiflorum). Both LMADS3 and LMADS4 mRNA were detected in the inflorescence meristem, in floral buds of different developmental stages, and in all four whorls of the flower organ. LMADS4 mRNA is also expressed in vegetative leaf and in the inflorescence stem where LMADS3 expression is absent. Transgenic Arabidopsis, which ectopically expresses LMADS3, showed novel phenotypes by significantly reducing plant size, flowering extremely early, and loss of floral determinacy. By contrast, 35S::LMADS4 transgenic plants were morphologically indistinguishable from wild-type plants. The early-flowering phenotype in 35S::LMADS3 transgenic Arabidopsis plants was correlated with the up-regulation of flowering time genes FT, SUPPRESSOR OF OVEREXPRESSION OF CO 1, LUMINIDEPENDENS, and flower meristem identity genes LEAFY and APETALA1. This result was further supported by the ability of 35S::LMADS3 to rescue the late-flowering phenotype in gigantea-1 (gi-1), constans-3 (co-3), and luminidependens-1 but not for ft-1 or fwa-1 mutants. The activation of these flowering time genes is, however, indirect because their expression was unaffected in plants transformed with LMADS3 fused with rat glucocorticoid receptor in the presence of both dexamethasone and cycloheximide.     

Functional conservation of MADS-box factors controlling floral organ identity in rice and Arabidopsis

Studies on MADS-box genes in Arabidopsis and other higher eudicotyledonous flowering plants have shown that they are key regulators of flower development. Since Arabidopsis and monocotyledonous rice are distantly related plant species it is interesting to investigate whether the floral organ identity factors have been conserved in their functions, and if not, to understand the differences. Arabidopsis and rice are very suitable for these studies since they are both regarded as models for plant functional genomics. Both their genomes are sequenced and tools are available for the analysis of gene function. These developments have accelerated experiments and increased our knowledge on rice gene function. Therefore it is the right moment to perform a comparative analysis on MADS-box factors controlling floral organ identity as reported in this review.     

Cloning and characterization of a bamboo LEAFY HULL STERILE1 homologous gene.

A cDNA named DlMADS8 was isolated from the young spikelets of the sweet bamboo, Dendrocalamus latiflorus by rapid amplification of cDNA end (RACE). DNA sequence analysis showed that DlMADS8 was composed of full ORF and 3'UTR, but without 5'UTR. The cDNA contained 1059 nucleotides and encoded a putative protein of 244 amino acid residues. The gene displayed the structure of a typical plant MADS-box gene, which consisted of a MADS domain, K domain, a short I region, and the C-terminal region. Phylogenetic analysis of plant MADS-box genes based on amino acid sequences revealed that DlMADS8 was grouped into the AGAMOUS-LIKE 2 (AGL2)-like subfamily. It was homologous to the LEAFY HULL STERILE1 (LHS1) genes of grasses. To study the functions of it, DlMADS8 cDNA clone driven by the CaMV 35S promoter was transformed into Arabidopsis thaliana. Transgenic plants of DlMADS8 exhibited the phenotypes of curled leaves and early flowering. After bolting, three novel phenotypes related to inflorescence development were observed in different transgenic plants. No obvious homeotic conversions of floral organs were observed in all of the 35S::DllMADS8 transgenic Arabidopsis plants. These results indicated that DlMADS8 probably plays a role in floral meristem determinacy and is involved in controlling the flowering time of D. latiflorus.     

MADS-BOX GENES: DEVELOPMENT AND EVOLUTION OF PLANT BODY PLANS

We review functional data on MADS-box genes, recent phylogenetic analyses of these coding regions, and their roles in the development and evolution of key morphological innovations in plants. We map the origin of important morphological structures in particular diverse stages of the life cycle in different plant clades onto organismal phylogenies, and present relevant molecular genetic aspects of development related to the MADS-box genes. We focus on reproductive structures of the sporophyte because most functional characterizations have been done of MADS-box genes involved in flower development. We discuss MADS-box evolution in flowering plants, but we also review studies in the other nonflowering vascular plants, gymnosperms (conifers and gnetales), and ferns and preliminary data from the algae. We suggest that floral (e.g. flowering time, inflorescence, and flower meristem identity) MADS-box and nonfloral plant MADS-box genes should be the focus of future comparative research. Cloning and functional analyses of MADS-box genes in bryophytes, particularly in the experimental system Physcomitrella patens (Hedw.) B.S.G., are needed. The ABC model of floral organ specification is an excellent general representation of an important network of genes; however, formal analytical tools are required to integrate data on complex gene interaction in comparative analyses. This and other analytical approaches to constructing gene network models will help to frame homology hypotheses in an evolutionary and developmental framework.     

Eucalyptus has a functional equivalent of the Arabidopsis floral meristem identity gene LEAFY

Two genes cloned from Eucalyptus globulus, Eucalyptus LeaFy (ELF1 and ELF2), have sequence homology to the floral meristem identity genes LEAFY from Arabidopsis and FLORICAULA from Antirrhinum. ELF1 is expressed in the developing eucalypt floral organs in a pattern similar to LEAFY while ELF2 appears to be a pseudo gene. ELF1 is expressed strongly in the early floral primordium and then successively in the primordia of sepals, petals, stamens and carpels. It is also expressed in the leaf primordia and young leaves and adult and juvenile trees.The ELF1 promoter coupled to a GUS reporter gene directs expression in transgenic Arabidopsis in a temporal and tissue-specific pattern similar to an equivalent Arabidopsis LEAFY promoter construct. Strong expression is seen in young flower buds and then later in sepals and petals. No expression was seen in rosette leaves or roots of flowering plants or in any non-flowering plants grown under long days. Furthermore, ectopic expression of the ELF1 gene in transgenic Arabidopsis causes the premature conversion of shoots into flowers, as does an equivalent 35S-LFY construct. These data suggest that ELF1 plays a similar role to LFY in flower development and that the basic mechanisms involved in flower initiation and development in Eucalyptus are similar to those in Arabidopsis.     

植物MADS-box基因的研究进展

MADS-box基因是一类重要的转录调控因子,在动物、植物、真菌中都有分布。在植物中从根、茎、叶到花的发育,果实的成熟MADS-box基因都起作用,尤其是在开花植物中花的发育,开花时间的控制等方面起着重要的作用。综述了MADS-box基因的分类、进化、结构、以及MADS-box基因在植物花器官发育,开花时间的控制,果实的成熟等方面的作用。     

Functional analysis of three lily (Lilium longiflorum) APETALA1-like MADS box genes in regulating floral transition and formation

Three cDNAs showing a high degree of homology to the SQUA subfamily of MADS box genes were isolated and characterized from the lily (Lilium longiflorum). Lily MADS Box Gene 5 (LMADS5) showed high sequence identity to oil palm (Elaeis guineensis) SQUAMOSA3 (EgSQUA3). LMADS6 is closely related to LMADS5 whereas LMADS7 is more related to DOMADS2, an orchid (Dendrobium) gene in the SQUA subfamily. The expression pattern for these three genes was similar and their RNAs were detected in vegetative stem and inflorescence meristem. LMADS5 and 6 were highly expressed in vegetative leaves and carpel, whereas LMADS7 expression was absent. Ectopic expression of LMADS5, 6 or 7 in transgenic Arabidopsis plants showed novel phenotypes by flowering early and producing terminal flowers. Homeotic conversions of sepals to carpelloid structures and of petal to stamen-like structures were also observed in 35S::LMADS5, 6 or 7 flowers. Ectopic expression of LMADS6 or LMADS7 was able to complement the ap1 flower defect in transgenic Arabidopsis ap1 mutant plants. These results strongly indicated that the function of these three lily genes was involved in flower formation as well as in floral induction. Furthermore, the ability of lily LMADS6 and 7 to complement the Arabidopsis ap1 mutant provided further evidence to show that the conserved motifs (paleoAP1 or euAP1) in the C-terminus of the SQUA/AP1 subfamily of MADS box genes is not strictly necessary for their function.     

利用抑制性差减杂交技术筛选草原龙胆花器官发育特性基因

目的:探讨草原龙胆花发育的分子机制,为进一步阐述花器官同源异型、属于MADS-box基因家族的一系列基因在调节开花植物花瓣和雄蕊的发育中的作用奠定基础。方法:以草原龙胆不同发育时期的花器官(萼片、花瓣、雄蕊、雌蕊)原基的cDNA作为试验方(tester),以茎叶组织的cDNA作为驱动方(driver),利用抑制性消减杂交技术构建了一个富集花器官发育特性基因的抑制性差减cDNA文库。对抑制性差减cDNA文库进行筛选、测序及Blast同源性比较。结果:获得了与花器官发育相关的特异性基因。结论:构建了抑制性差减cDNA文库,为克隆草原龙胆花器官发育特异性基因全长序列奠定了基础。     

A short history of MADS-box genes in plants

Evolutionary developmental genetics (evodevotics) is a novel scientific endeavor which assumes that changes in developmental control genes are a major aspect of evolutionary changes in morphology. Understanding the phylogeny of developmental control genes may thus help us to understand the evolution of plant and animal form. The principles of evodevotics are exemplified by outlining the role of MADS-box genes in the evolution of plant reproductive structures. In extant eudicotyledonous flowering plants, MADS-box genes act as homeotic selector genes determining floral organ identity and as floral meristem identity genes. By reviewing current knowledge about MADS-box genes in ferns, gymnosperms and different types of angiosperms, we demonstrate that the phylogeny of MADS-box genes was strongly correlated with the origin and evolution of plant reproductive structures such as ovules and flowers. It seems likely, therefore, that changes in MADS-box gene structure, expression and function have been a major cause for innovations in reproductive development during land plant evolution, such as seed, flower and fruit formation.     

Comparative analysis of rice MADS-box genes expressed during flower development

MADS-box genes involved in flower development have been isolated and studied in a wide variety of plant species. However, most of these studies are related to dicot species like Antirrhinum majus, Arabidopsis thaliana and Petunia hybrida. Although the floral structures of typical monocot and dicot flowers differ substantially, previous studies indicate that MADS-box genes controlling floral organ identity in dicots can also be identified in monocot plants like rice and maize. To extend this study further to obtain a more global picture of monocot and dicot MADS-box gene evolution, we performed a phylogenetic study using MADS-box genes from A. thaliana and Oryza sativa. Furthermore, we investigated whether the identified orthologues of Arabidopsis and rice have a conserved expression profile that could indicate conservation of function.