Diverse roles for MADS box genes in Arabidopsis development.

Members of the MADS box gene family play important roles in flower development from the early step of determining the identity of floral meristems to specifying the identity of floral organ primordia later in flower development. We describe here the isolation and characterization of six additional members of this family, increasing the number of reported Arabidopsis MADS box genes to 17. All 11 members reported prior to this study are expressed in flowers, and the majority of them are floral specific. RNA expression analyses of the six genes reported here indicate that two genes, AGL11 and AGL13 (AGL for AGAMOUS-like), are preferentially expressed in ovules, but each has a distinct expression pattern. AGL15 is preferentially expressed in embryos, with its onset at or before the octant stage early in embryo development. AGL12, AGL14, and AGL17 are all preferentially expressed in root tissues and therefore represent the only characterized MADS box genes expressed in roots. Phylogenetic analyses showed that the two genes expressed in ovules are closely related to previously isolated MADS box genes, whereas the four genes showing nonfloral expression are more distantly related. Data from this and previous studies indicate that in addition to their proven role in flower development, MADS box genes are likely to play roles in many other aspects of plant development.     

leafy hull sterile1 is a homeotic mutation in a rice MADS box gene affecting rice flower development

Rice contains several MADS box genes. It has been demonstrated previously that one of these genes, OsMADS1 (for Oryza sativa MADS box gene1), is expressed preferentially in flowers and causes early flowering when ectopically expressed in tobacco plants. In this study, we demonstrated that ectopic expression of OsMADS1 in rice also results in early flowering. To further investigate the role of OsMADS1 during rice flower development, we generated transgenic rice plants expressing altered OsMADS1 genes that contain missense mutations in the MADS domain. There was no visible alteration in the transgenic plants during the vegetative stage. However, transgenic panicles typically exhibited phenotypic alterations, including spikelets consisting of elongated leafy paleae and lemmas that exhibit a feature of open hull, two pairs of leafy palea-like and lemma-like lodicules, a decrease in stamen number, and an increase in the number of carpels. In addition, some spikelets generated an additional floret from the same rachilla. These characteristics are very similar to those of leafy hull sterile1 (lhs1). The map position of OsMADS1 is closely linked to that of lhs1 on chromosome 3. Examination of lhs1 revealed that it contains two missense mutations in the OsMADS1 MADS domain. A genetic complementation experiment showed that the 11.9-kb genomic DNA fragment containing the wild-type OsMADS1 gene rescued the mutant phenotypes. In addition, ectopic expression of the OsMADS1 gene isolated from the lhs1 line resulted in lhs1-conferred phenotypes. These lines of evidence demonstrate that OsMADS1 is the lhs1 gene.     

A petunia MADS box gene involved in the transition from vegetative to reproductive development.

We have identified a novel petunia MADS box gene, PETUNIA FLOWERING GENE (PFG), which is involved in the transition from vegetative to reproductive development. PFG is expressed in the entire plant except stamens, roots and seedlings. Highest expression levels of PFG are found in vegetative and inflorescence meristems. Inhibition of PFG expression in transgenic plants, using a cosuppression strategy, resulted in a unique nonflowering phenotype. Homozygous pfg cosuppression plants are blocked in the formation of inflorescences and maintain vegetative growth. In these mutants, the expression of both PFG and the MADS box gene FLORAL BINDING PROTEIN26 (FBP26), the putative petunia homolog of SQUAMOSA from Antirrhinum, are down-regulated. In hemizygous pfg cosuppression plants initially a few flowers are formed, after which the meristem reverts to the vegetative phase. This reverted phenotype suggests that PFG, besides being required for floral transition, is also required to maintain the reproductive identity after this transition. The position of PFG in the hierarchy of genes controlling floral meristem development was investigated using a double mutant of the floral meristem identity mutant aberrant leaf and flower (alf) and the pfg cosuppression mutant. This analysis revealed that the pfg cosuppression phenotype is epistatic to the alf mutant phenotype, indicating that PFG acts early in the transition to flowering. These results suggest that the petunia MADS box gene, PFG, functions as an inflorescence meristem identity gene required for the transition of the vegetative shoot apex to the reproductive phase and the maintenance of reproductive identity.     

Ancestral MADS box genes in Sugi, Cryptomeria japonica D. Don (Taxodiaceae), homologous to the B function genes in angiosperms.

In flowering plants, flower organ identity is controlled by the ABC genes, including several MADS box genes. We present two MADS box genes of a conifer, Cryptomeria japonica D. Don. The genes, CjMADS1 and CjMADS2, were related to the angiosperm B function genes which determine the identities of petals and stamens. A phylogenetic analysis showed that these genes form a new clade outside the angiosperm B group, that is, PISTILLATA (PI) and APETALA3 (AP3) lineages. CjMADS1 had a PI-group specific motif and CjMADS2 had AP3-group specific motifs at the C terminal end, respectively. CjMADS1 was expressed in male strobili (or cones) throughout its development, while CjMADS2 was transiently expressed during male strobilus development. The specific expression in the male reproductive organ indicated that the B function is maintained in gymnosperms. Our cladistic analysis suggests that the gene duplication event which generated B function gene lineages predates the divergence of angiosperms and gymnosperms and that the gene duplication which produced the two genes of C. japonica occurred in an ancestral conifer species.     

Cloning and characterization of four apple MADS box genes isolated from vegetative tissue

With the aim of finding genes involved in the floral transition of woody species four MADS box genes containing cDNAs from apple (Malus domestica) have been isolated. Three genes were isolated from vegetative tissue of apple, but were homologues of known genes that specify floral organ identity. MdMADS13 is an AP3-like B class MADS box gene, and was mainly expressed in petals and stamens as demonstrated by Northern blot analysis. MdMADS14 and -15 are AGAMOUS-like genes. They differed slightly in expression patterns on Northern blots, with MdMADS15 mRNA levels equally high in stamens and carpels, but MdMADS14 preferably expressed in carpels. MdMADS14 is likely to be the apple orthologue of one of the Arabidopsis thaliana SHATTERPROOF genes, and MdMADS15 closely resembled the Arabidopsis AGAMOUS gene. It has been shown with RT-PCR that the three floral apple MADS box genes are expressed in vegetative tissues of adult as well as juvenile trees, albeit at low levels. MdMADS12 is an AP1-like gene that is expressed at similar levels in leaves, vegetative shoots, and floral tissues, and that may be involved in the transition from the juvenile to the adult stage.     

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.     

Ectopic expression of carpel-specific MADS box genes from lily and lisianthus causes similar homeotic conversion of sepal and petal in Arabidopsis

Two MADS box genes, Lily MADS Box Gene 2 (LMADS2) and Eustoma grandiflorum MADS Box Gene 1 (EgMADS1), with an extensive similarity to the petunia (Petunia hybrida) FLORAL BINDING PROTEIN 7/11 and Arabidopsis AGL11, were characterized from the lily (Lilium longiflorum) and lisianthus (Eustoma grandiflorum). The expression of LMADS2 and EgMADS1 mRNA was restricted to the carpel and was absent in the other flower organs or vegetative leaves. LMADS2 mRNA was detected mainly in ovules and weakly in style tissues of the carpel, whereas EgMADS1 mRNA was only expressed in the ovules. Transgenic Arabidopsis plants ectopically expressing LMADS2 or EgMADS1 showed similar novel phenotypes resembling 35S::AGAMOUS plants by significantly reducing plant size, flowering early, and losing inflorescence indeterminacy. Ectopic expression of these two genes also generated similar ap2-like flowers by inducing homeotic conversion of the sepals into carpel-like structures in which stigmatic papillae and ovules were observed. In addition, the petals were converted into stamen-like structures in the second whorl of 35S::LMADS2 and 35S::EgMADS1 transgenic Arabidopsis. Our data indicated that LMADS2 and EgMADS1 are putative D functional MADS box genes in lily and lisianthus with a function similar to C functional genes once ectopically expressed in Arabidopsis.     

An orchid (Oncidium Gower Ramsey) AP3-like MADS gene regulates floral formation and initiation

cDNA for a B group MADS box gene OMADS3 was isolated and characterized from Oncidium Gower Ramsey, an important species of orchid. OMADS3 encoding a 204 amino acid protein showed high sequence homology to both paleoAP3 and TM6 lineage of B group MADS box gene such as monocots AP3 homologue LMADS1 in lily and GDEF1 in Gerbera hybrida. Despite the sequence homology, consensus motifs identified in the C-terminal region of B group genes were absent in OMADS3. Southern analysis indicated that OMADS3 was present in O. Gower Ramsey genome in low copy numbers. Different from most B group genes, OMADS3 mRNA was detected in all four floral organs as well as in vegetative leaves. This is similar to the expression pattern of GDEF1. 35S::OMADS3 transgenic plants showed novel phenotypes by producing terminal flowers similar to those observed in transgenic plants ectopically expressed A functional genes such as AP1. Ectopic expression of OMADS3 cDNA truncated with the MADS box or C terminal region in Arabidopsis generated novel ap2-like flowers in which sepals and petals were converted into carpel-like and stamen-like structures. Yeast two-hybrid analysis indicated that OMADS3 is able to strongly form homodimers. Our results suggested that OMADS3 might represent an ancestral form of TM6-like gene which was conserved in monocots with a function similar to A functional gene in regulating flower formation as well as floral initiation.     

<Emphasis Type="Italic">AOM3</Emphasis> and<Emphasis Type="Italic"> AOM4</Emphasis>: two MADS box genes expressed in reproductive structures of<Emphasis Type="Italic"> Asparagus officinalis</Emphasis>

The MADS box genes participate in different steps of vegetative and reproductive plant development, including the most important phases of the reproductive process. Here we describe the isolation and characterisation of two Asparagus officinalis MADS box genes, AOM3 and AOM4. The deduced AOM3 protein shows the highest degree of similarity with ZAG3 and ZAG5 of maize, OsMADS6 of rice and AGL6 of Arabidopsis thaliana. The deduced AOM4 protein shows the highest degree of similarity with AOM1 of asparagus, the SEP proteins of Arabidopsis and the rice proteins OsMADS8, OsMADS45 and OsMADS7. The high level of identity between AOM1 and AOM4 made impossible the preparation of probes specific for one single gene, so the hybridisation signal previously described for AOM1 is probably due to the expression of both genes. The expression profile of AOM3 and AOM1/AOM4 during flower development is identical, and similar to that of the SEP genes. Asparagus genes, however, are expressed not only in flower organs, but also in the different meristem present on the apical region of the shoot during the flowering season: the apical meristem and the three lateral meristems emerging from the leaf axillary region that will give rise to flowers and lateral inflorescences during flowering season, and to phylloclades and branches during the subsequent vegetative phase. The expression of AOM3 and AOM1/AOM4 in these meristems appears to be correlated with the reproductive function of the apex as the hybridisation signal disappears when the apex switches to vegetative function.     

麝香百合LLGLO1基因的克隆和表达

用RACE方法克隆的麝香百合花发育的GLOBOSA（GLO）类B功能基因LLGLO1,与其他多种单子叶植物的GLO类基因高度同源,且C区具有典型的PI结构基序。通过RT—PCR检测,百合不同组织中的LLGLO1基因表达模式与郁金香的GLO类基因相似。即主要集中在百合第一、二、三轮花器官中表达,心皮和茎中有微量表达,而且随着心皮的成熟,其在心皮中的表达量逐渐增加,但在百合叶片中则未检测到LLGLO1的表达,因此认为LLGLO1在百合花器官中呈特异性表达。LLGLO1在百合第一轮花器官中的表达支持了van Tunen对ABC模型的修正。