Terminal Flower Research Articles

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.

An efficient sampling scheme for monitoring flowering of Actinidia chinensis

Flowering data from four vines of Actinidia chinensis (Planch.) var. chinensis ’Hort16A’ and three vines of A. chinensis ’37–3‐18A’ ('18A') were used to develop a robust and efficient scheme to monitor flowering. The frequency distribution of flowering for ‘Hort16A’ flowers was normal. Although the distribution of flowering for ‘18A’ terminal flowers was not normal, assuming normality produced estimates of the date and standard deviation of mid bloom within1 day of the true value. Three schemes for selecting shoots for monitoring flowering in A. chinensis vines were tested. The accuracy of flowering estimates was proportional to the number of shoots monitored and although totally random selection of shoots was slightly more accurate, stratified random and systematic sampling was more practical. Flowering can be monitored at 4‐day, rather than 2‐day intervals without affecting the accuracy of estimates. For the two cultivars we tested, monitoring flowering on 60 shoots selected using the stratified random and systematic scheme will result in estimates of mid bloom within ±1 day of the true value on 80–95% of occasions. This corresponds to a sampling intensity of c. 3–4% of the total number of terminal flowers on the vine, or 140–290 flowers/population.

Contrasting evolutionary forces in the Arabidopsis thaliana floral developmental pathway.

The floral developmental pathway in Arabidopsis thaliana is composed of several interacting regulatory genes, including the inflorescence architecture gene TERMINAL FLOWER1 (TFL1), the floral meristem identity genes LEAFY (LFY), APETALA1 (AP1), and CAULIFLOWER (CAL), and the floral organ identity genes APETALA3 (AP3) and PISTILLATA (PI). Molecular population genetic analyses of these different genes indicate that the coding regions of AP3 and PI, as well as AP1 and CAL, share similar levels and patterns of nucleotide diversity. In contrast, the coding regions of TFL1 and LFY display a significant reduction in nucleotide variation, suggesting that these sequences have been subjected to a recent adaptive sweep. Moreover, the promoter of TFL1, unlike its coding region, displays high levels of diversity organized into two distinct haplogroups that appear to be maintained by selection. These results suggest that patterns of molecular evolution differ among regulatory genes in this developmental pathway, with the earlier acting genes exhibiting evidence of adaptive evolution.

Overexpression of RCN1 and RCN2, rice TERMINAL FLOWER 1/CENTRORADIALIS homologs, confers delay of phase transition and altered panicle morphology in rice.

TERMINAL FLOWER 1 (TFL1)/CENTRORADIALIS (CEN)-like genes play important roles in determining plant architecture, mainly by controlling the timing of phase transition. To investigate the possibility of similar mechanisms operating in the control of inflorescence architecture in rice, we analysed the functions of RCN1 and RCN2, rice TFL1/CEN homologs. Constitutive overexpression of RCN1 or RCN2 in Arabidopsis caused a late-flowering and highly branching phenotype, indicating that they possess conserved biochemical functions as TFL1. In 35S::RCN1 and 35S::RCN2 transgenic rice plants, the delay of transition to the reproductive phase was observed. The transgenic rice plants exhibited a more branched, denser panicle morphology. Detailed observation of the panicle structure revealed that the phase change from the branch shoot to the floral meristem state was also delayed, leading to the generation of higher-order panicle branches. These results suggest rice has a pathway that can respond to the overexpressed TFL1/CEN-like functions, and the molecular mechanisms controlling the phase transition of meristems are conserved between grass and dicot species, at least to some extent.

Overexpression of MdMADS5, an APETALA1-like gene of apple, causes early flowering in transgenic Arabidopsis

An apple ( Malus× domestica) gene MdMADS5, a putative homolog of Arabidopsis APETALA1 ( AP1) and Antirrhinum SQUAMOSA, was introduced into Arabidopsis using Agrobacterium tumefaciens EHA101 to examine how the gene affects flowering and whether it may be effective in producing transgenic apple that flowers early. Five of the 15 primarily transformed ( T 1) plants flowered 5–10 days earlier than wild-type plants and produced only two to three rosette leaves when they flowered. The terminal flowers on the transgenic plants resembled transgenic Arabidopsis expressing 35S:: AP1 or tfl1 mutant plants. This phenotype observed in T 1 transgenic plants was inherited in the following generation. Based on these results, it was suggested that the function of the MdMADS5 gene was similar to that of the AP1 gene. Although the mechanism of flower-bud formation in the apple might be different from that in Arabidopsis, the MdMADS5 gene might be involved in flower-bud formation of the apple.

Comparative morphology of Cladopus (including Torrenticola, Podostemaceae) from East Asia to north-eastern Australia

Cladopus (with 12 or less species) is an Asian and Australian genus of Podostemaceae–Podostemoideae. They are haptophytes that grow in rivers. The developmental morphology and anatomy of Cladopus austro-osumiensis Y.Kadono & N.Usui, C. austrosatsumensis Koidzumi, C. chinensis Chao, C. japonicus Imamura and C. queenslandicus [Domin] C.D.K. Cook & Rutish. (syn. Torrenticola queenslandica [Domin] Domin ex Steenis) are studied by scanning electron microscope and microtome. The architecture of the examined species fits with the bauplan known from other Asian Podostemoideae. Rosulate shoots arise in zigzag patterns or as opposite pairs from narrow or broad green ribbons which may be interpreted as adhesive creeping roots. Cladopus is the only podostemaceous genus known with both endogenous and exogenous lateral roots along the mother root. Exogenous lobes (which may develop into daughter roots) are next to the sites of root-borne shoots which, finally, give rise to terminal flowers. Cladopus species have the following features (synapomorphies) in common: (1) leaves on older and reproductive shoots with one or two median, long filaments (caducous) and 1–4 lateral short lobes (persistent) on either side of the leaf, which are called stipules; (2) spathella (i.e. mantle-like flower cover) with an apical two-tipped papilla; (3) spathella splitting more or less circumscissilely; (4) capsules globose or nearly so, smooth or with three faint ribs per valve.

Flower differentiation and spur leaf area in almond

SummaryIn mature almond trees, flowers are borne laterally and predominantly on spurs. The flower buds contain a single terminal flower and no leaves. We investigated variation in the timing of floral initiation and organogenesis among and within spurs on ‘Nonpareil’ almond (Prunus dulcis [Mill.] D. A. Webb). Spurs were sampled twice during the late-summer period of flower initiation and differentiation. All lateral buds on individual spurs were dissected and the developmental status of the meristem was determined. Extensive variation in the progress of floral initiation and differentiation was evident among spurs. Spurs with high total leaf areas had more floral buds, and these buds underwent transition to flowering and floral organogenesis earlier than buds on spurs with lower total leaf areas. Within spurs, there was no gradient in floral development relative to bud position on the spur. The results indicate that spurs function independently with regard to floral development events, and suggest that within spurs buds may function somewhat independently as well.

The questionable affinities of Lactoris: evidence from branching pattern, inflorescence morphology, and stipule development

The phylogenetically ambivalent monotypic genus Lactoris presents sympodial (determinate) branching, as a terminal flower is present on each main branch. The synflorescence is thyrsoid. Partial inflorescences are rhipidia with up to three flowers. The ochrealike stipule is formed by the fusion of two lateral stipules, which forms an adaxial ligule-like structure and a two-flanked leaf sheath that encircles the parental axis. The leaf sheath elongates with the growth of the preceding internode. Although sympodial growth and a sheathing leaf base are present in all Piperales (Aristolochiaceae, Lactoridaceae, Piperaceae, and Saururaceae), the presence of stipules is confined to Lactoris, Saururaceae, and some Piperaceae. These characters are consistent with the placement of Lactoris within Piperales, although its phylogenetic position within the order remains equivocal, except for the possible sister group relationship suggested by the presence of cymose inflorescences in both Lactoris and Aristolochiaceae.

Selection of Day-neutral, Heat-delay-insensitive Dendranthem×grandiflora Genotypes

Commercial garden and greenhouse chrysanthemums [Dendranthema ×grandiflora (Ramat.) Kitam. (syn. Chrysanthemum xmorifolium Ramat.)] are facultative short-day plants for flower bud initiation, obligate short-day plants for flower bud development, and are categorized into short-day response groups. Flower initiation can be delayed by high night temperatures. Recent research has identified true day-neutral genotypes. The purpose of this investigation was to test environments for selecting genotypes that are both day-neutral and heat-delay insensitive. One greenhouse and 18 garden genotypes were selected. A series of environments were used to select for day-neutral genotypes and then differentiate between these genotypes for heat delay insensitivity: short days, long days/red light, long days/far red light and high temperatures, and natural day lengths under field conditions. Day-neutral selections from these environments were then grown in a fifth environment of long days/continuous far red and red light with high temperature. Data were collected on the number of days to first and third flower, long day leaf number, stem length, number of strap-shaped leaves subtending the terminal flower, internode lengths, number of nodes with axillary branching, and flower bud development of the first to the sixth flowers. Genotypes required 3 to 8 weeks for complete flower bud initiation/development. Flowering responses in the first four environments were highly significant for both the first and third flowers. Genotypes ranged from obligate short-day to day-neutral for the first six flowers. Three day-neutral genotypes were selected that differed significantly for all traits in the fifth environment; flower bud development with the first six flowers occurred with only one genotype, 83-267-3. Broad sense heritability estimates ranged from h2 = 0.75 for number of nodes with axillary branching, h2 = 0.79 for long day leaf number and number of strap-shaped leaves, to h2 = 0.91 for stem length. An ideotype for day-neutral and heat-delay-insensitive garden chrysanthemums was developed for use in breeding programs.

Male and hermaphrodite flowers in the alpine lily Lloydia serotina

In perennial species that produce only one flower per individual each year, androdiœcy (coexistence of genetic male and hermaphrodite individuals) may be difficult to distinguish from andromonœcy (male and hermaphrodite flowers on the same plant). We show that the alpine lily, Lloydia serotina Rchb., produces functionally male and hermaphroditic flowers. Mean male frequency in 11 populations in the French Alps was 48.5%, ranging from 15.5 to 67.5%. Male flowers do not produce more pollen nor sire more seeds per flower in controlled pollinations than hermaphrodite flowers. Male floral scapes were consistently shorter than those of hermaphrodites. Out of several thousand observed floral scapes, four had two flowers, all with a terminal hermaphroditic flower and an axillary male one. Among 107 bulbs transplanted in pots in 1996, eighteen expressed a different sexual phenotype in 1999 or 2000, and one hermaphrodite produced two flowers of different sexes in 2000. Together, these results suggest that L. serotina is andromonœcious throughout its lifetime.Key words: Lloydia serotina, andromonœcy, male reproductive success, Liliaceae.

EMF1, a novel protein involved in the control of shoot architecture and flowering in Arabidopsis.

Shoot architecture and flowering time in angiosperms depend on the balanced expression of a large number of flowering time and flower meristem identity genes. Loss-of-function mutations in the Arabidopsis EMBRYONIC FLOWER (EMF) genes cause Arabidopsis to eliminate rosette shoot growth and transform the apical meristem from indeterminate to determinate growth by producing a single terminal flower on all nodes. We have identified the EMF1 gene by positional cloning. The deduced polypeptide has no homology with any protein of known function except a putative protein in the rice genome with which EMF1 shares common motifs that include nuclear localization signals, P-loop, and LXXLL elements. Alteration of EMF1 expression in transgenic plants caused progressive changes in flowering time, shoot determinacy, and inflorescence architecture. EMF1 and its related sequence may belong to a new class of proteins that function as transcriptional regulators of phase transition during shoot development.

The delayed terminal flower phenotype is caused by a conditional mutation in the CENTRORADIALIS gene of snapdragon.

The snapdragon (Antirrhinum majus) centroradialis mutant (cen) is characterized by the development of a terminal flower, thereby replacing the normally open inflorescence by a closed inflorescence. In contrast to its Arabidopsis counterpart, terminal flower1, the cen-null mutant displays an almost constant number of lateral flowers below the terminal flower. Some partial revertants of an X-radiation-induced cen mutant showed a delayed formation of the terminal flower, resulting in a variable number of lateral flowers. The number of lateral flowers formed was shown to be environmentally controlled, with the fewer flowers formed under the stronger flower-inducing conditions. Plants displaying this "Delayed terminal flower" phenotype were found to be heterozygous for a mutant allele carrying a transposon in the coding region and an allele from which the transposon excised, leaving behind a 3-bp duplication as footprint. As a consequence, an iso-leucine is inserted between Asp148 and Gly149 in the CENTRORADIALIS protein. It is proposed that this mutation results in a low level of functional CEN activity, generating a phenotype that is more similar to the Arabidopsis Terminal flower phenotype.

The Developmental Basis of Floral Variation inDrimys winteri(Winteraceae)

Flowers within a tree of Drimys winteri vary markedly in floral organ number and arrangement. This variation can be linked to developmental differences between flowers in different parts of the inflorescence. Floral organ number varies most markedly between terminal and lateral flowers, whereas variation in organ arrangement is correlated with the shape of the flower. Key events during development, including changes in meristem shape and a delay in initiation of petals, allow a remarkable variety of whorled and spiral phyllotactic patterns to arise. Relatively few flowers showed Fibonacci phyllotaxis, which is otherwise very common in plant systems. Variation in divergence angle within flowers is correlated with meristem shape, whereas variation in plastochron ratio is shown to depend both on meristem shape and on divergence angle. Differences in floral morphology are interpreted as the result of an ordered process of initiation of primordia superimposed on variation in the symmetry of the floral meristem...

Variation in flowering within Actinidia chinensis vines

Variation in the time of flowering within vines of two Actinidia chinensis (Planch.) var. chinensis cultivars, ‘Hortl6A’ and ‘37–3‐18A’ ('18A'), is described. The flowering capacity of the two cultivars was very different, with 106 terminal flowers and 50 lateral flowers/m2 of canopy on ‘18A’ vines compared to only 39 terminal flowers/m2 on ‘Hortl6A’ vines. However the variation within vines was similar. The most consistent systematic trend in the time of flowering was within canes, where time of flowering varied by up to 7 days. Shoots near the apex of the cane produced more flowers and they opened earlier than shoots near the cordon. Vines of both cultivars produced a large number of canes near the trunk and few at the end of cordons. However, time of flowering was not consistently affected by position on the cordon, cane size, or type of fruiting wood. On ‘ 18A’ vines, lateral flowers formed a separate population, opening 4–5 days after terminal flowers, and should be monitored separately. Any sampling scheme developed from these data should take account of variation within canes. Vines should be managed to reduce variation in flowering date, which has been linked to unwanted variation in fruit maturity at harvest.

Alteration in flowering time causes accelerated or decelerated progression throughArabidopsisvegetative phases

We have identified three phases within the wild-type Arabidopsis thaliana (L.) Heynh. rosette, based on significant differences in leaf shape, size, vascular pattern, and presence of abaxial trichomes. To test the hypothesis that a single, central mechanism controls the progression through all plant phases and that conditions that alter the time to flowering will also alter the progression through vegetative phases, we analysed the rosette phases under such conditions. In support of our hypothesis, we determined that those conditions (loss of LEAFY activity, short days) that decelerate time to flowering show decelerated progression through the rosette phases, while those conditions (loss of TERMINAL FLOWER, overexpression of LEAFY, low light) that accelerate time to flowering show accelerated progression through the rosette phases. In all conditions except short days, the length of the first phase was unaffected, indicating that this phase is less susceptible to influences of the central mechanism. Progression through the subsequent two rosette phases was accelerated differentially, such that the second phase was affected more strongly than the first. This supports the idea that, in the rosette, as in the inflorescence, the inhibition of phase transition by the central mechanism is gradually decreasing.Key words: phase change, flowering time, Arabidopsis thaliana, LEAFY, TERMINAL FLOWER, heteroblasty.

A NewBRACTEA(BRA) Gene Controlling the Formation of an Indeterminate Bractless Inflorescence in Arabidopsis thaliana

The morphological and genetic studies of the bramutant of Arabidopsis thaliana(L.) Heynh. from the collection of the Department of Genetics and Breeding, Moscow State University, showed that the BRAgene controls the major stages of inflorescence development: it suppresses the development of leaves subtending flowers (bracts) and inhibits the formation of the terminal flower. Inactivation of the BRAgene leads to the transition from the indeterminate bractless inflorescence characteristic of the family Cruciferaceae to the determinate bracteose inflorescence. It is suggested that the BRAgene is a regulator gene probably involved in the conversion of the bracteose determinate inflorescence to the indeterminate ebracteate inflorescence during the origin of ancestral crucifers.

Prenylation of the Floral Transcription Factor APETALA1 Modulates Its Function

The Arabidopsis MADS box transcription factor APETALA1 (AP1) was identified as a substrate for farnesyltransferase and shown to be farnesylated efficiently both in vitro and in vivo. AP1 regulates the transition from inflorescence shoot to floral meristems and the development of sepals and petals. AP1 fused to green fluorescent protein (GFP) retained transcription factor activity and directed the expected terminal flower phenotype when ectopically expressed in transgenic Arabidopsis. However, ap1mS, a farnesyl cysteine-acceptor mutant of AP1, as well as the GFP-ap1mS fusion protein failed to direct the development of compound terminal flowers but instead induced novel phenotypes when ectopically expressed in Arabidopsis. Similarly, compound terminal flowers did not develop in era1-2 transformants that ectopically expressed AP1. Together, the results demonstrate that AP1 is a target of farnesyltransferase and suggest that farnesylation alters the function and perhaps specificity of the transcription factor.

Floral development and structure of Davidsonia (Cunoniaceae)

Few data on floral development and morphology are available for the monotypic Australian genus Davidsonia. New data on floral form and development are presented for Davidsonia, and comparisons are made to allied clades. Phylogenetic analysis allies Davidsonia with core Cunoniaceae. Flower maturation on each branch of the cauliflorous inflorescences is basipetal, beginning with the terminal flower. Flowers are hypogynous, radially symmetrical, and have a uniseriate perianth that consists of a campanulate calyx. Davidsonia has been traditionally allied with Cunoniaceae, and it shares various basic floral attributes, especially gynoecial states, with some members of this family. The bicarpellate gynoecium of Davidsonia has an ovary that is completely synorganized and biloculate, two separate styles that have prominent ventral commissures, and terminal, papillate stigmas. Davidsonia differs most from core Cunoniaceae in androecial morphology, including the development of the androecium and the form of stamens. The stamens of Davidsonia display a mosaic of states present among members of Oxalidales (including Cephalotaceae, Cunoniaceae, Elaeocarpaceae, and Tremandraceae) in which the genus is nested. Although Davidsonia shares various floral states with Cunoniaceae, it can best be perceived as displaying a mosaic of features that occur more broadly among Oxalidales.Key words: Cunoniaceae, Davidsonia, flower development, morphology, Oxalidales.

Redundant regulation of meristem identity and plant architecture by FRUITFULL, APETALA1 and CAULIFLOWER.

The transition from vegetative to reproductive phases during Arabidopsis development is the result of a complex interaction of environmental and endogenous factors. One of the key regulators of this transition is LEAFY (LFY), whose threshold levels of activity are proposed to mediate the initiation of flowers. The closely related APETALA1 (AP1) and CAULIFLOWER (CAL) meristem identity genes are also important for flower initiation, in part because of their roles in upregulating LFY expression. We have found that mutations in the FRUITFULL (FUL) MADS-box gene, when combined with mutations in AP1 and CAL, lead to a dramatic non-flowering phenotype in which plants continuously elaborate leafy shoots in place of flowers. We demonstrate that this phenotype is caused both by the lack of LFY upregulation and by the ectopic expression of the TERMINAL FLOWER1 (TFL1) gene. Our results suggest that the FUL, AP1 and CAL genes act redundantly to control inflorescence architecture by affecting the domains of LFY and TFL1 expression as well as the relative levels of their activities.

Floral development and structure of <i>Davidsonia</i> (Cunoniaceae)

Few data on floral development and morphology are available for the monotypic Australian genus Davidsonia. New data on floral form and development are presented for Davidsonia, and comparisons are made to allied clades. Phylogenetic analysis allies Davidsonia with core Cunoniaceae. Flower maturation on each branch of the cauliflorous inflorescences is basipetal, beginning with the terminal flower. Flowers are hypogynous, radially symmetrical, and have a uniseriate perianth that consists of a campanulate calyx. Davidsonia has been traditionally allied with Cunoniaceae, and it shares various basic floral attributes, especially gynoecial states, with some members of this family. The bicarpellate gynoecium of Davidsonia has an ovary that is completely synorganized and biloculate, two separate styles that have prominent ventral commissures, and terminal, papillate stigmas. Davidsonia differs most from core Cunoniaceae in androecial morphology, including the development of the androecium and the form of stamens...