Inflorescence Branches Research Articles

Analysis of two TFL1 homologs of dogwood species (Cornus L.) indicates functional conservation in control of transition to flowering.

Two TFL1 -like genes, CorfloTFL1 and CorcanTFL1 cloned from Cornus florida and C. canadensis, function in regulating the transition to reproductive development in Arabidopsis. TERMINAL FLOWER 1 (TFL1) is known to regulate inflorescence development in Arabidopsis thaliana and to inhibit the transition from a vegetative to reproductive phase within the shoot apical meristem. Despite the importance, TFL1 homologs have been functionally characterized in only a handful eudicots. Here we report the role of TFL1 homologs of Cornus L. in asterid clade of eudicots. Two TFL1-like genes, CorfloTFL1 and CorcanTFL1, were cloned from Cornus florida (a tree) and C. canadensis (a subshrub), respectively. Both are deduced to encode proteins of 175 amino acids. The amino acid sequences of these two Cornus TFL1 homologs share a high similarity to Arabidopsis TFL1 and phylogenetically more close to TFL1 paralogous copy ATC (Arabidopsis thaliana CENTRORADIALIS homologue). Two genes are overexpressed in wild-type and tfl1 mutant plants of A. thaliana. The over-expression of each gene in wild-type Arabidopsis plants results in delaying flowering time, increase of plant height and cauline and rosette leaf numbers, excessive shoot buds, and secondary inflorescence branches. The over-expression of each gene in the tfl1 mutant rescued developmental defects, such as the early determinate inflorescence development, early flowering time, and other vegetative growth defects, to normal phenotypes of wild-type plants. These transgenic phenotypes are inherited in progenies. All data indicate that CorfloTFL1 and CorcanTFL1 have conserved the ancestral function of TFL1 and CEN regulating flowering time and inflorescence determinacy.

SUPPRESSOR OF APICAL DOMINANCE1 of Sporisorium reilianum Modulates Inflorescence Branching Architecture in Maize and Arabidopsis.

The biotrophic fungus Sporisorium reilianum causes head smut of maize (Zea mays) after systemic plant colonization. Symptoms include the formation of multiple female inflorescences at subapical nodes of the stalk because of loss of apical dominance. By deletion analysis of cluster 19-1, the largest genomic divergence cluster in S. reilianum, we identified a secreted fungal effector responsible for S. reilianum-induced loss of apical dominance, which we named SUPPRESSOR OF APICAL DOMINANCE1 (SAD1). SAD1 transcript levels were highly up-regulated during biotrophic fungal growth in all infected plant tissues. SAD1-green fluorescent protein fusion proteins expressed by recombinant S. reilianum localized to the extracellular hyphal space. Transgenic Arabidopsis (Arabidopsis thaliana)-expressing green fluorescent protein-SAD1 displayed an increased number of secondary rosette-leaf branches. This suggests that SAD1 manipulates inflorescence branching architecture in maize and Arabidopsis through a conserved pathway. Using a yeast (Saccharomyces cerevisiae) two-hybrid library of S. reilianum-infected maize tissues, we identified potential plant interaction partners that had a predicted function in ubiquitination, signaling, and nuclear processes. Presence of SAD1 led to an increase of the transcript levels of the auxin transporter PIN-FORMED1 in the root and a reduction of the branching regulator TEOSINTE BRANCHED1 in the stalk. This indicates a role of SAD1 in regulation of apical dominance by modulation of branching through increasing transcript levels of the auxin transporter PIN1 and derepression of bud outgrowth.

Inflorescence development in theVitis-Ampelocissusclade of Vitaceae: the unusual lamellate inflorescence ofPterisanthes

Pterisanthes (Vitaceae) is a genus of c. 20 species of scandent climbers endemic to Southeast Asia with unusual lamellate inflorescences. Molecular phylogenetic analysis supports its relationship in the well‐supported Vitis–Ampelocissus–Nothocissus–Pterisanthes clade (i.e. the Ampelocissus–Vitis clade). Shoot tips and floral buds were collected from wild and greenhouse‐grown P. eriopoda at different developmental stages and were examined using epi‐illumination, light and scanning electron microscopy. Inflorescence and floral ontogeny was studied to discover how the lamellate inflorescence evolved and to make morphological comparisons to infer relationships with closely related members of Vitaceae. The second‐order branches in P. eriopoda are racemose and develop helically around the inflorescence axis in a similar fashion to Vitis and Ampelocissus. Inflorescence branching is restricted to the second order in P. eriopoda, whereas in Vitis and most Ampelocissus species subsequent branching orders culminate in the typical vitaceous determinate dichasium. In P. eriopoda subsequent lateral growth of the second‐order branches combined with the inhibition of peduncle or pedicel formation and loss of dichasial branching results in the unique lamellae in Pterisanthes, on which the floral primordia arise directly in a helical pattern. Floral development in P. eriopoda is the same as in other genera of Vitaceae examined to date with initiation of floral whorls centripetally, the calyx ring developing first and calyx lobes fused to cover the petals and stamen primordia. Given the recent phylogenetic results that placed Pterisanthes firmly within Ampelocissus, the most likely scenario is that the Pterisanthes inflorescence is derived from the thyrse of an Ampelocissus‐like ancestor and that the thyrse is a morphological synapomorphy of the Ampelocissus–Vitis clade. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179, 725–741.

Mutations in Barley Row Type Genes Have Pleiotropic Effects on Shoot Branching.

Cereal crop yield is determined by different yield components such as seed weight, seed number per spike and the tiller number and spikes. Negative correlations between these traits are often attributed to resource limitation. However, recent evidence suggests that the same genes or regulatory modules can regulate both inflorescence branching and tillering. It is therefore important to explore the role of genetic correlations between different yield components in small grain cereals. In this work, we studied pleiotropic effects of row type genes on seed size, seed number per spike, thousand grain weight, and tillering in barley to better understand the genetic correlations between individual yield components. Allelic mutants of nine different row type loci (36 mutants), in the original spring barley varieties Barke, Bonus and Foma and introgressed in the spring barley cultivar Bowman, were phenotyped under greenhouse and outdoor conditions. We identified two main mutant groups characterized by their relationships between seed and tillering parameters. The first group comprises all mutants with an increased number of seeds and significant change in tiller number at early development (group 1a) or reduced tillering only at full maturity (group 1b). Mutants in the second group are characterized by a reduction in seeds per spike and tiller number, thus exhibiting positive correlations between seed and tiller number. Reduced tillering at full maturity (group 1b) is likely due to resource limitations. In contrast, altered tillering at early development (groups 1a and 2) suggests that the same genes or regulatory modules affect inflorescence and shoot branching. Understanding the genetic bases of the trade-offs between these traits is important for the genetic manipulation of individual yield components.

Evolution and divergence of SBP-box genes in land plants.

BackgroundSquamosa promoter binding protein (SBP)-box family genes encode plant-specific transcription factors that control many important biological functions, including phase transition, inflorescence branching, fruit ripening, and copper homeostasis. Nevertheless, the evolutionary patterns of SBP-box genes and evolutionary forces driving them are still not well understood.Methods104 SBP-box gene candidates of five representative land plants were obtained from Phytozome database (v10.3). Phylogenetic combined with gene structure analyses were used to identify SBP-box gene lineages in land plants. Gene copy number and the sequence and structure features were then compared among these different SBP-box lineages. Selection analysis, relative rate tests and expression divergence were finally used to interpret the evolutionary relationships and divergence of SBP-box genes in land plants.ResultsWe investigated 104 SBP-box genes from moss, Arabidopsis, poplar, rice, and maize. These genes are divided into group I and II, and the latter is further divided into two subgroups (subgroup II-1 and II-2) based on phylogenetic analysis. Interestingly, subgroup II-1 genes have similar sequence and structural features to group I genes, whereas subgroup II-2 genes exhibit intrinsic differences on these features, including high copy numbers and the presence of miR156/miR529 regulation. Further analyses indicate that subgroup II-1 genes are constrained by stronger purifying selection and evolve at a lower substitution rate than II-2 genes, just as group I genes do when compared to II genes. Among subgroup II-2 genes, miR156 targets evolve more rapidly than miR529 targets and experience comparatively relaxed purifying selection. These results suggest that group I and subgroup II-1 genes under strong selective constraint are conserved. By contrast, subgroup II-2 genes evolve under relaxed purifying selection and have diversified through gene copy duplications and changes in miR156/529 regulation, which might contribute to morphological diversifications of land plants.ConclusionsOur results indicate that different evolutionary rates and selection strengths lead to differing evolutionary patterns in SBP-box genes in land plants, providing a guide for future functional diversity analyses of these genes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1998-y) contains supplementary material, which is available to authorized users.

Grape SISTER OF RAMOSA3 is a negative regulator of pedicel development of grape inflorescence

We report here the relationship between pedicel development and grape SISTER OF RAMOSA3 (VvSRA) expression in grapevine. The increase in VvSRA expression, but not grape RAMOSA3 expression, in young grape inflorescence decreased the number of pedicels on the lateral branch of grape inflorescence. This suggests that VvSRA negatively regulates pedicel development on the lateral branch of grape inflorescence, thereby decreasing berry number on a bunch in cultivars expressing VvSRA abundantly. Similarly, VvSRA overexpression decreased the number of flower buds on secondary branch in Arabidopsis plants. In addition, VvSRA overexpression had notable effects on Arabidopsis plant phenotypes, such as smaller flowers, shorter inflorescence, and expanded rosette leaves. As VvSRA encodes a trehalose 6-phosphate phosphatase, VvSRA overexpression might decrease trehalose 6-phosphate in the transgenic Arabidopsis plants, thereby causing the phenotypical alternations. These findings may provide new information on grapevine morphogenesis including pedicel development by SISTER OF RAMOSA3 and trehalose metabolism.

Phenotypic Diversity of Nepalese Finger Millet (Eleusine coracana (L.) Gaertn.) Accessions at IAAS, Rampur, Nepal

An experiment was conducted at Institute of Agriculture and Animal Science (IAAS), Rampur, Nepal during July 2011 to September 2011 with an objectine to determine phenotypic variability of Nepalese finger millet landraces using descriptive statistics, cluster analysis and principal component analysis. F- Value of REML procedure of mixed model analysis revealed that highly significant variation was observed in all studied 17 traits. Grain yield per plant was positive and highly significant correlated with grain yield per ear (0.769**) followed by plant height (0.529**), productive tillers number (0.473**), days to maturity (0.471**), days to heading (0.460**), days to flowering (0.457**), straw yield per plant (0.348**), finger number per ear (0.320**), thousand kernel weight (0.281**), flag leaf sheath width (0.230**) and finger length (0.211**). The ear shape (H’= 3.42) followed by grain color (H’= 3.35) showed high genetic diversity after estimated by using Shannon- Weaver index. 46% open type ear shape, 40% light brown grain color, 66% non-pigmentation, 70% absence of inflorescence branch and 54% absence of finger branch were found dominant to other on studied accessions. The distribution pattern was observed by using Ward’s minimumvariance method into five clusters. The number of accessions in a cluster was ranged from 18 in cluster IV to 1 in cluster V. The cluster V (accession no. 10996) and III (accessions no. 431 and 11024) showed early phenological traits, lowest in finger length, finger width, finger number per ear, thousand kernel weight, grain yield per ear and grain yield per plant. The cluster II and IV showed late maturity type, long finger length and width, high in finger number per ear, grain yield per ear, grain yield per plant and plant height. The first five principal components accounted for 74.9% of total variance among 50 accessions. Most of variation was contributed from phenological characters, plant height, grain yield per ear, finger length, finger width, finger number per ear and productive tillers number. These traits were positively correlated with grain yield and can be used in selection for breeding programs.Int J Appl Sci Biotechnol, Vol 3(2): 285-290 DOI: http://dx.doi.org/10.3126/ijasbt.v3i2.12413

A cascade of arabinosyltransferases controls shoot meristem size in tomato

Shoot meristems of plants are composed of stem cells that are continuously replenished through a classical feedback circuit involving the homeobox WUSCHEL (WUS) gene and the CLAVATA (CLV) gene signaling pathway. In CLV signaling, the CLV1 receptor complex is bound by CLV3, a secreted peptide modified with sugars. However, the pathway responsible for modifying CLV3 and its relevance for CLV signaling are unknown. Here we show that tomato inflorescence branching mutants with extra flower and fruit organs due to enlarged meristems are defective in arabinosyltransferase genes. The most extreme mutant is disrupted in a hydroxyproline O-arabinosyltransferase and can be rescued with arabinosylated CLV3. Weaker mutants are defective in arabinosyltransferases that extend arabinose chains, indicating that CLV3 must be fully arabinosylated to maintain meristem size. Finally, we show that a mutation in CLV3 increased fruit size during domestication. Our findings uncover a new layer of complexity in the control of plant stem cell proliferation.

Analysis of the transcriptional responses in inflorescence buds of Jatropha curcas exposed to cytokinin treatment.

BackgroundJatropha curcas L. is a potential biofuel plant. Application of exogenous cytokinin (6-benzyladenine, BA) on its inflorescence buds can significantly increase the number of female flowers, thereby improving seed yield. To investigate which genes and signal pathways are involved in the response to cytokinin in J. curcas inflorescence buds, we monitored transcriptional activity in inflorescences at 0, 3, 12, 24, and 48 h after BA treatment using a microarray.ResultsWe detected 5,555 differentially expressed transcripts over the course of the experiment, which could be grouped into 12 distinct temporal expression patterns. We also identified 31 and 131 transcripts in J. curcas whose homologs in model plants function in flowering and phytohormonal signaling pathways, respectively. According to the transcriptional analysis of genes involved in flower development, we hypothesized that BA treatment delays floral organ formation by inhibiting the transcription of the A, B and E classes of floral organ-identity genes, which would allow more time to generate more floral primordia in inflorescence meristems, thereby enhancing inflorescence branching and significantly increasing flower number per inflorescence. BA treatment might also play an important role in maintaining the flowering signals by activating the transcription of GIGANTEA (GI) and inactivating the transcription of CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) and TERMINAL FLOWER 1b (TFL1b). In addition, exogenous cytokinin treatment could regulate the expression of genes involved in the metabolism and signaling of other phytohormones, indicating that cytokinin and other phytohormones jointly regulate flower development in J. curcas inflorescence buds.ConclusionsOur study provides a framework to better understand the molecular mechanisms underlying changes in flowering traits in response to cytokinin treatment in J. curcas inflorescence buds. The results provide valuable information related to the mechanisms of cross-talk among multiple phytohormone signaling pathways in woody plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0318-z) contains supplementary material, which is available to authorized users.

Regulation of inflorescence architecture by cytokinins.

In flowering plants, the arrangement of flowers on a stem becomes an inflorescence, and a huge variety of inflorescence architecture occurs in nature. Inflorescence architecture also affects crop yield. In simple inflorescences, flowers form on a main stem; by contrast, in compound inflorescences, flowers form on branched stems and the branching pattern defines the architecture of the inflorescence. In this review, we highlight recent findings on the regulation of inflorescence architecture by cytokinin plant hormones. Results in rice (Oryza sativa) and Arabidopsis thaliana show that although these two species have distinct inflorescence architectures, cytokinins have a common effect on inflorescence branching. Based on these studies, we discuss how cytokinins regulate distinct types of inflorescence architecture through their effect on meristem activities.

SASP, a Senescence-Associated Subtilisin Protease, is involved in reproductive development and determination of silique number in Arabidopsis.

Senescence involves increased expression of proteases, which may participate in nitrogen recycling or cellular signalling. 2D zymograms detected two protein species with increased proteolytic activity in senescing leaves of Arabidopsis thaliana. A proteomic analysis revealed that both protein species correspond to a subtilisin protease encoded by At3g14067, termed Senescence-Associated Subtilisin Protease (SASP). SASP mRNA levels and enzyme activity increase during leaf senescence in leaves senescing during both the vegetative or the reproductive phase of the plant life cycle, but this increase is more pronounced in reproductive plants. SASP is expressed in all above-ground organs, but not in roots. Putative AtSASP orthologues were identified in dicot and monocot crop species. A phylogenetic analysis shows AtSASP and its putative orthologues clustering in one discrete group of subtilisin proteases in which no other Arabidospsis subtilisin protease is present. Phenotypic analysis of two knockout lines for SASP showed that mutant plants develop more inflorescence branches during reproductive development. Both AtSASP and its putative rice orthologue (OsSASP) were constitutively expressed in sasp-1 to complement the mutant phenotype. At maturity, sasp-1 plants produced 25% more inflorescence branches and siliques than either the wild-type or the rescued lines. These differences were mostly due to an increased number of second and third order branches. The increased number of siliques was compensated for by a small decrease (5.0%) in seed size. SASP downregulates branching and silique production during monocarpic senescence, and its function is at least partially conserved between Arabidopsis and rice.

Seed-to-seed-to-seed growth and development of Arabidopsis in microgravity.

Arabidopsis thaliana was grown from seed to seed wholly in microgravity on the International Space Station. Arabidopsis plants were germinated, grown, and maintained inside a growth chamber prior to returning to Earth. Some of these seeds were used in a subsequent experiment to successfully produce a second (back-to-back) generation of microgravity-grown Arabidopsis. In general, plant growth and development in microgravity proceeded similarly to those of the ground controls, which were grown in an identical chamber. Morphologically, the most striking feature of space-grown Arabidopsis was that the secondary inflorescence branches and siliques formed nearly perpendicular angles to the inflorescence stems. The branches grew out perpendicularly to the main inflorescence stem, indicating that gravity was the key determinant of branch and silique angle and that light had either no role or a secondary role in Arabidopsis branch and silique orientation. Seed protein bodies were 55% smaller in space seed than in controls, but protein assays showed only a 9% reduction in seed protein content. Germination rates for space-produced seed were 92%, indicating that the seeds developed in microgravity were healthy and viable. Gravity is not necessary for seed-to-seed growth of plants, though it plays a direct role in plant form and may influence seed reserves.

Characterization of a Multiseeded (msd1) Mutant of Sorghum for Increasing Grain Yield

ABSTRACTSorghum [Sorghum bicolor (L.) Moench] has branched panicles with primary, secondary, and tertiary branches. These inflorescence branches are composed of a terminal triplet spikelet, consisting of one sessile (directly attached to the branch) and two pedicellate (spikelets attached to the branch through a short pedicel), followed by one or more spikelet pairs (one sessile and one pedicellate). In BTx623, and most sorghum lines, only the sessile spikelets can develop into seeds and the pedicellate spikelets, occasionally developing anthers, eventually abort. Here, we report the isolation and characterization of a stable multiseeded (msd1) mutant of sorghum (in BTx623 background, referred to as wild‐type [WT]) in which both sessile and pedicellate spikelets are fertile. In addition, this mutant displayed increased length and total number of primary and secondary inflorescence branches. Genetic analysis showed that this multiseeded mutation is a recessive trait. Pedicellate spikelets in msd1 mutants exhibited complete flower with functional ovary and anthers, of which 75 to 95% can develop into viable seeds. The individual msd1 seeds are smaller than WT; however, the results indicated that this reduction in seed weight can be compensated by the increase in seed number. The total seed weight per panicle in msd1 mutants was increased by 30 to 40% as compared to the WT. Further experiments are needed to demonstrate whether the msd1 mutation can increase grain yield under field conditions.

Miconia indicoviolacea (Melastomataceae: Miconieae): a new Colombian species from the western flanks of the cordillera Occidental

Miconia indicoviolacea is described from the western slopes of the western cordillera in the Chocó biogeographic region of Colombia, illustrated, and compared with superficially similar species that are also endemic to the country. It is readily recognized by its prevailingly purple to dark blue inflorescence branches, peduncles, and internodes, minute glandular-puberulent vegetative and hypanthial indumentum, caudate foliar apex, dorsally inclined anther pores, glabrous rounded to truncate dorso-basal staminal appendages, and seeds with a conspicuous appendage at the chalazal end and a raphal zone that is approximately double the size of the seed corpus.

Regulation of inflorescence branch development in rice through a novel pathway involving the pentatricopeptide repeat protein sped1-D.

Panicle type has a direct bearing on rice yield. Here, we characterized a rice clustered-spikelet mutant, sped1-D, with shortened pedicels and/or secondary branches, which exhibits decreased pollen fertility. We cloned sped1-D and found that it encodes a pentatricopeptide repeat protein. We investigated the global expression profiles of wild-type, 9311, and sped1-D plants using Illumina RNA sequencing. The expression of several GID1L2 family members was downregulated in the sped1-D mutant, suggesting that the gibberellin (GA) pathway is involved in the elongation of pedicels and/or secondary branches. When we overexpressed one GID1L2, AK070299, in sped1-D plants, the panicle phenotype was restored to varying degrees. In addition, we analyzed the expression of genes that function in floral meristems and found that RFL and WOX3 were severely downregulated in sped1-D. These results suggest that sped1-D may prompt the shortening of pedicels and secondary branches by blocking the action of GID1L2, RFL, and Wox3. Moreover, overexpression of sped1-D in Arabidopsis resulted in the shortening of pedicels and clusters of siliques, which indicates that the function of sped1-D is highly conserved in monocotyledonous and dicotyledonous plants. Sequence data from this article have been deposited with the miRBase Data Libraries under accession no. MI0003201.

Comparison of Flowering Phenology of Two Kinds of Sandy Semi-shrub of Artemisia L. in the Horqin Sandy Land

The flowering phenology of Artemisia wudanica and A. halodendron were investigated at four levels( capitulum,inflorescence branches,individual and population) in the Horqin Sandy Land. The results showed that:(1) At the population level,the initial time of flowering of A.wudanica was18th June,which was9d earlier than A.halodendron,the durations were 19 d and 16 d,respectively,and the overlapping flowering period was 10 d in two species. At the individual level,the initial time of flowering was 7 d earlier and the duration was 2 d longer in A.wudanica than in A. halodendron;( 2) The number of capitulum on secondary inflorescence branches was less and duration was longer in A. wudanica than in A. halodendron. The flowering frequency of two species were all singlepeak type,the highest frequency of flowering duration time at the secondary inflorescence branch were all 8 d,followed by 9 d; for the capitulum,the higher frequency were all 5 d,4 d,6 d and the highest one was 5 d;( 3) The first flowering position was near the base of secondary inflorescence branches in A. halodendron,the highest frequency was the second and the third one from the base,being 12. 7% and 11. 9%,respectively. However,the capitulum on the top of secondary inflorescence branches was the first blossom in A. wudanica,the frequency was up to 56. 3%;( 4) The flowering amplitude curve of two species all showed a single peak curve,A. wudanica reached its peak on the 9th day after flowering,and A. halodendron was on the 6th day. The similarity of these two species' flowering phenology reflected their phylogenetic relationship and adaptability to environment. The differences,especially the first flowering position,indicated the genetic differences in long-term evolution of two species.

A new species of Arundinella (Poaceae: Panicoideae: Arundinelleae) from Kerala, India

Arundinella pradeepiana Sunil et Naveen Kumar, a new species from the Poaceae, collected from rocky grassland in the Variyam forest of Ernakulam district, Kerala, India is described and illustrated. The new species is allied to Arundinella metzii Hochst. ex Miq., but differs in having tubercle-based soft hairy nodes, profusely branched primary inflorescence branches and 1.4–2 mm long, deep brown upper lemmas that are granulate or muricate at their distal half.

Erratum: Identification of novel transcription factors regulating secondary cell wall formation in Arabidopsis

A commentary on Identification of novel transcription factors regulating secondary cell wall formation in ArabidopsisBy Cassan-Wang H. et al (2013). Front Plant Sci. 2013; 4: 189. doi: 10.3389/fpls.2013.00189Published online Jun 11, 2013. Prepublished online Apr 10, 2013. After our article was published on line, we noticed that a typographical mistake occured in the name of an Arabidopsis mutant : p 6 , in the results, last paragraph of the section « phenotypes of the TF T-DNA mutant or RNAi transgenic lines », One should read hb5 instead of hb15Here is the corrected textThe overall growth behavior of the mutants did not differ significantly from the controls, except the bolting and flowering time were altered in three of the mutant lines. Hypolignified blh6 and zinc finger lines bolted and flowered earlier than controls (Figures 5A,C) whereas the hyperlignified hb5 line exhibited delayed bolting and flowering (Figures 5B,C). In addition, hb5 mutants exhibited aerial rosettes at the base of the lateral inflorescence branches instead of growing cauline leaves as in wild-type plants (Figure (Figure5D).

Trehalose metabolism in plants

Trehalose is a quantitatively important compatible solute and stress protectant in many organisms, including green algae and primitive plants. These functions have largely been replaced by sucrose in vascular plants, and trehalose metabolism has taken on new roles. Trehalose is a potential signal metabolite in plant interactions with pathogenic or symbiotic micro-organisms and herbivorous insects. It is also implicated in responses to cold and salinity, and in regulation of stomatal conductance and water-use efficiency. In plants, as in other eukaryotes and many prokaryotes, trehalose is synthesized via a phosphorylated intermediate, trehalose 6-phosphate (Tre6P). A meta-analysis revealed that the levels of Tre6P change in parallel with sucrose, which is the major product of photosynthesis and the main transport sugar in plants. We propose the existence of a bi-directional network, in which Tre6P is a signal of sucrose availability and acts to maintain sucrose concentrations within an appropriate range. Tre6P influences the relative amounts of sucrose and starch that accumulate in leaves during the day, and regulates the rate of starch degradation at night to match the demand for sucrose. Mutants in Tre6P metabolism have highly pleiotropic phenotypes, showing defects in embryogenesis, leaf growth, flowering, inflorescence branching and seed set. It has been proposed that Tre6P influences plant growth and development via inhibition of the SNF1-related protein kinase (SnRK1). However, current models conflict with some experimental data, and do not completely explain the pleiotropic phenotypes exhibited by mutants in Tre6P metabolism. Additional explanations for the diverse effects of alterations in Tre6P metabolism are discussed.

Gibberellin acts positively then negatively to control onset of flower formation in Arabidopsis.

The switch to reproductive development is biphasic in many plants, a feature important for optimal pollination and yield. We show that dual opposite roles of the phytohormone gibberellin underpin this phenomenon in Arabidopsis. Although gibberellin promotes termination of vegetative development, it inhibits flower formation. To overcome this effect, the transcription factor LEAFY induces expression of a gibberellin catabolism gene; consequently, increased LEAFY activity causes reduced gibberellin levels. This allows accumulation of gibberellin-sensitive DELLA proteins. The DELLA proteins are recruited by SQUAMOSA PROMOTER BINDING PROTEIN-LIKE transcription factors to regulatory regions of the floral commitment gene APETALA1 and promote APETALA1 up-regulation and floral fate synergistically with LEAFY. The two opposing functions of gibberellin may facilitate evolutionary and environmental modulation of plant inflorescence architecture.