Response of plant development to environment: control of flowering by daylength and temperature

CONSTANS, a HUB for all seasons: How photoperiod pervades plant physiology regulatory circuits

How does a plant detect the changing seasons and make important developmental decisions accordingly? How do they incorporate daylength information into their routine physiological processes? Photoperiodism, or the capacity to measure the daylength, is a crucial aspect of plant development that helps plants determine the best time of the year to make vital decisions, such as flowering. The protein CONSTANS (CO) constitutes the central regulator of this sensing mechanism, not only activating florigen production in the leaves but also participating in many physiological aspects in which seasonality is important. Recent discoveries place CO in the center of a gene network that can determine the length of the day and confer seasonal input to aspects of plant development and physiology as important as senescence, seed size, or circadian rhythms. In this review, we discuss the importance of CO protein structure, function, and evolutionary mechanisms that embryophytes have developed to incorporate annual information into their physiology.

Above and belowground phenotypic response to exogenous auxin across Arabidopsis thaliana mutants and natural accessions varies from seedling to reproductive maturity

Background

Plant hormones influence phenology, development, and function of above and belowground plant structures. In seedlings, auxin influences the initiation and development of lateral roots and root systems. How auxin-related genes influence root initiation at early life stages has been investigated from numerous perspectives. There is a gap in our understanding of how these genes influence root size through the life cycle and in mature plants. Across development, the influence of a particular gene on plant phenotypes is partly regulated by the addition of a poly-A tail to mRNA transcripts via alternative polyadenylation (APA). Auxin related genes have documented variation in APA, with auxin itself contributing to APA site switches. Studies of the influence of exogenous auxin on natural plant accessions and mutants of auxin pathway gene families exhibiting variation in APA are required for a more complete understanding of genotype by development by hormone interactions in whole plant and fitness traits.

Methods

We studied Arabidopsis thaliana homozygous mutant lines with inserts in auxin-related genes previously identified to exhibit variation in number of APA sites. Our growth chamber experiment included wildtype Col-0 controls, mutant lines, and natural accession phytometers. We applied exogenous auxin through the life cycle. We quantified belowground and aboveground phenotypes in 14 day old, 21 day old seedlings and plants at reproductive maturity. We contrasted root, rosette and flowering phenotypes across wildtype, auxin mutant, and natural accession lines, APA groups, hormone treatments, and life stages using general linear models.

Results

The root systems and rosettes of mutant lines in auxin related genes varied in response to auxin applications across life stages and varied between genotypes within life stages. In seedlings, exposure to auxin decreased size, but increased lateral root density, whereas at reproductive maturity, plants displayed greater aboveground mass and total root length. These differences may in part be due to a shift which delayed the reproductive stage when plants were treated with auxin. Root traits of auxin related mutants depended on the number of APA sites of mutant genes and the plant's developmental stage. Mutants with inserts in genes with many APA sites exhibited lower early seedling belowground biomass than those with few APA sites but only when exposed to exogenous auxin. As we observed different responses to exogenous auxin across the life cycle, we advocate for further studies of belowground traits and hormones at reproductive maturity. Studying phenotypic variation of genotypes across life stages and hormone environments will uncover additional shared patterns across traits, assisting efforts to potentially reach breeding targets and enhance our understanding of variation of genotypes in natural systems.

Genome-wide detection of genotype environment interactions for flowering time in Brassica napus

Flowering time is strongly related to the environment, while the genotype-by-environment interaction study for flowering time is lacking in Brassica napus. Here, a total of 11,700,689 single nucleotide polymorphisms in 490 B. napus accessions were used to associate with the flowering time and related climatic index in eight environments using a compressed variance-component mixed model, 3VmrMLM. As a result, 19 stable main-effect quantitative trait nucleotides (QTNs) and 32 QTN-by-environment interactions (QEIs) for flowering time were detected. Four windows of daily average temperature and precipitation were found to be climatic factors highly correlated with flowering time. Ten main-effect QTNs were found to be associated with these flowering-time-related climatic indexes. Using differentially expressed gene (DEG) analysis in semi-winter and spring oilseed rapes, 5,850 and 5,511 DEGs were found to be significantly expressed before and after vernalization. Twelve and 14 DEGs, including 7 and 9 known homologs in Arabidopsis, were found to be candidate genes for stable QTNs and QEIs for flowering time, respectively. Five DEGs were found to be candidate genes for main-effect QTNs for flowering-time-related climatic index. These candidate genes, such as BnaFLCs, BnaFTs, BnaA02.VIN3, and BnaC09.PRR7, were further validated by the haplotype, selective sweep, and co-expression networks analysis. The candidate genes identified in this study will be helpful to breed B. napus varieties adapted to particular environments with optimized flowering time.

Adaptation to novel environments during crop diversification

In the context of the global challenge of climate change, mitigation strategies are needed to adapt crops to novel environments. The main goal to address this is an understanding of the genetic basis of crop adaptation to different agro-ecological conditions. The movement of crops during the Colombian Exchange that started with the travels of Columbus in 1492 is an example of rapid adaptation to novel environments. Many diversification-related traits have been characterised in multiple crop species, and association-mapping analyses have identified loci involved in these. Here, we present an overview of current knowledge regarding the molecular basis related to the complex patterns of crop adaptation and dissemination, particularly outside their centres of origin. Investigation of the genomic basis of crop expansion offers a powerful contribution to the development of tools to identify and exploit valuable genetic diversity and to improve and design novel resilient crop varieties.

Synchronization of photoperiod and temperature signals during plant thermomorphogenesis

It is well-known that even small changes in ambient temperatures by a few degrees profoundly affect plant growth and morphology. This architectural property is intimately associated with global warming. In particular, under warm temperature conditions, plants exhibit distinct morphological changes, such as elongation of hypocotyls and leaf petioles, formation of small, thin leaves, and leaf hyponasty that describes an upward bending of leaf petioles. These thermoresponsive morphological adjustments are termed thermomorphogenesis. Under warm temperature conditions, the PHYTOCHROME INTERACTING FACTOR 4 (PIF4) transcription factor is thermoactivated and stimulates the transcription of the YUCCA8 gene encoding an auxin biosynthetic enzyme, promoting hypocotyl elongation. Notably, these thermomorphogenic growth is influenced by daylength or photoperiod, displaying relatively high and low thermomorphogenic hypocotyl growth during the nighttime under short days and long days, respectively. We have recently reported that the photoperiod signaling regulator GIGANTEA (GI) thermostabilizes the REPRESSOR OF ga1-3 transcription factor, which is known to attenuate the PIF4-mediated thermomorphogenesis. We also found that the N-terminal domain of GI interacts with PIF4, possibly destabilizing the PIF4 proteins. We propose that the GI-mediated shaping of photoperiodic rhythms of hypocotyl thermomorphogenesis helps plant adapt to fluctuations in daylength and temperature environments occurring during seasonal transitions.

Pleiotropy in developmental regulation by flowering-pathway genes: is it an evolutionary constraint?

Pleiotropy occurs when one gene influences more than one trait, contributing to genetic correlations among traits. Consequently, it is considered a constraint on the evolution of adaptive phenotypes because of potential antagonistic selection on correlated traits, or, alternatively, preservation of functional trait combinations. Such evolutionary constraints may be mitigated by the evolution of different functions of pleiotropic genes in their regulation of different traits. Arabidopsis thaliana flowering-time genes, and the pathways in which they operate, are among the most thoroughly studied regarding molecular functions, phenotypic effects, and adaptive significance. Many of them show strong pleiotropic effects. Here, we review examples of pleiotropy of flowering-time genes and highlight those that also influence seed germination. Some genes appear to operate in the same genetic pathways when regulating both traits, whereas others show diversity of function in their regulation, either interacting with the same genetic partners but in different ways or potentially interacting with different partners. We discuss how functional diversification of pleiotropic genes in the regulation of different traits across the life cycle may mitigate evolutionary constraints of pleiotropy, permitting traits to respond more independently to environmental cues, and how it may even contribute to the evolutionary divergence of gene function across taxa.

Lasy-Seq: a high-throughput library preparation method for RNA-Seq and its application in the analysis of plant responses to fluctuating temperatures

RNA-Seq is a whole-transcriptome analysis method used to research biological mechanisms and functions but its use in large-scale experiments is limited by its high cost and labour requirements. In this study, we have established a high-throughput and cost-effective RNA-Seq library preparation method that does not require mRNA enrichment. The method adds unique index sequences to samples during reverse transcription (RT) that is conducted at a higher temperature (≥62 °C) to suppress RT of A-rich sequences in rRNA, and then pools all samples into a single tube. Both single-read and paired-end sequencing of libraries is enabled. We found that the pooled RT products contained large amounts of RNA, mainly rRNA, causing over-estimations of the quantity of DNA and unstable tagmentation results. Degradation of RNA before tagmentation was found to be necessary for the stable preparation of libraries. We named this protocol low-cost and easy RNA-Seq (Lasy-Seq) and used it to investigate temperature responses in Arabidopsis thaliana. We analysed how sub-ambient temperatures (10-30 °C) affected the plant transcriptomes using time-courses of RNA-Seq from plants grown in randomly fluctuating temperature conditions. Our results suggest that there are diverse mechanisms behind plant temperature responses at different time scales.

Isolation and functional characterization of a floral repressor, BcFLC2, from Pak-choi (Brassica rapa ssp. chinensis)

BcFLC2 functioned as a repressor of flowering by directly regulating BcTEM1, BcMAF2, BcSOC1 and BcSPL15 in Pak-choi. FLOWERING LOCUS C (FLC) plays an important role in regulating flowering time. Here, we functionally described an FLC homologous gene, BcFLC2, that negatively regulated flowering in Pak-choi (Brassica rapa ssp. chinensis). The sequence comparison to Arabidopsis FLC showed that BcFLC2 also had a MADS-box domain at the N terminus. BcFLC2 was highly expressed in the leaves, roots, stems and stamens, and its expression was repressed by vernalization in Pak-choi. Interestingly, BcFLC2 expression exhibited a small peak at 2 weeks of vernalization treatment, suggesting that BcFLC2 may be involved in preventing premature flowering under short-term cold exposure in Pak-choi, which is different from the AtFLC expression pattern. Overexpression of BcFLC2 in Arabidopsis caused late flowering, while silencing of BcFLC2 in Pak-choi caused early flowering. BcFLC2 localized to the cell nucleus and functioned as a transcription factor. Yeast one-hybrid analysis revealed that BcFLC2 could bind to the promoters of Pak-choi Tempranillo 1 (BcTEM1), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (BcSOC1), SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 15 (BcSPL15) and MADS AFFECTING FLOWERING 2 (BcMAF2). Taken together, the present results suggested that BcFLC2 played a key role in flowering regulation as a negative regulator by controlling BcTEM1, BcMAF2, BcSOC1 and BcSPL15 expression.

Comparative analysis of the pteridophyte Adiantum MFT ortholog reveals the specificity of combined FT/MFT C and N terminal interaction with FD for the regulation of the downstream gene AP1

To study the evolution of phosphatidylethanolamine-binding protein (PEBP) gene families in non-flowering plants, we performed a functional analysis of the PEBP gene AcMFT of the MFT clade in the pteridophyte Adiantum capillus-veneris. The expression of AcMFT was regulated by photoperiod similar to that for FT under both long day and short day conditions. Ectopic expression of AcMFT in Arabidopsis promotes the floral transition and partially complements the late flowering defect in transgenic Arabidopsis ft-1 mutants, suggesting that AcMFT functions similarly to FT in flowering plants. Interestingly, a similar partial compensation of the ft-1 late flowering phenotype was observed in Arabidopsis ectopically expressing only exon 4 of the C terminus of AcMFT and FT. This result indicated that the fourth exon of AcMFT and FT plays a similar and important role in promoting flowering. Further analysis indicated that exons 1-3 in the N terminus specifically enhanced the function of FT exon 4 in controlling flowering in Arabidopsis. Protein pull-down assays indicated that Arabidopsis FD proteins interact with full-length FT and AcMFT, as well as peptides encoded by 1-3 exon fragments or the 4th exon alone. Furthermore, similar FRET efficiencies for FT-FD and AcMFT-FD heterodimer in nucleus were observed. These results indicated that FD could form the similar complex with FT and AcMFT. Further analysis indicated that the expression of AP1, a gene downstream of FT, was up-regulated more strongly by FT than AcMFT in transgenic Arabidopsis. Our results revealed that AcMFT from a non-flowering plant could interact with FD to regulate the floral transition and that this function was reduced due to the weakened ability of AcMFT-FD to activate the downstream gene AP1.

Sex-Biased Temporal Gene Expression in Male and Female Floral Buds of Seabuckthorn (Hippophae rhamnoides)

Seabuckthorn is an economically important dioecious plant in which mechanism of sex determination is unknown. The study was conducted to identify seabuckthorn homologous genes involved in floral development which may have role in sex determination. Forty four putative Genes involved in sex determination (GISD) reported in model plants were shortlisted from literature survey, and twenty nine seabuckthorn homologous sequences were identified from available seabuckthorn genomic resources. Of these, 21 genes were found to differentially express in either male or female flower bud stages. HrCRY2 was significantly expressed in female flower buds only while HrCO had significant expression in male flowers only. Among the three male and female floral development stages (FDS), male stage II had significant expression of most of the GISD. Information on these sex-specific expressed genes will help in elucidating sex determination mechanism in seabuckthorn.

Conserved CO-FT regulons contribute to the photoperiod flowering control in soybean

BACKGROUND

CO and FT orthologs, belonging to the BBX and PEBP family, respectively, have important and conserved roles in the photoperiod regulation of flowering time in plants. Soybean genome experienced at least three rounds of whole genome duplications (WGDs), which resulted in multiple copies of about 75% of genes. Subsequent subfunctionalization is the main fate for paralogous gene pairs during the evolutionary process.

RESULTS

The phylogenic relationships revealed that CO orthologs were widespread in the plant kingdom while FT orthologs were present only in angiosperms. Twenty-eight CO homologous genes and twenty-four FT homologous genes were gained in the soybean genome. Based on the collinear relationship, the soybean ancestral CO ortholog experienced three WGD events, but only two paralogous gene pairs (GmCOL1/2 and GmCOL5/13) survived in the modern soybean. The paralogous gene pairs, GmCOL1/2 or GmCOL5/13, showed similar expression patterns in pair but different between pairs, indicating that they functionally diverged. GmFTL1 to 7 were derived from the same ancestor prior to the whole genome triplication (WGT) event, and after the Legume WGD event the ancestor diverged into two branches, GmFTL3/5/7 and GmFTL1/2/4/6. GmFTL7 were truncated in the N-terminus compared to other FT-lineage genes, but ubiquitously expressed. Expressions of GmFTL1 to 6 were higher in leaves at the flowering stage than that at the seedling stage. GmFTL3 was expressed at the highest level in all tissues except roots at the seedling stage, and its circadian pattern was different from the other five ones. The transcript of GmFTL6 was highly accumulated in seedling roots. The circadian rhythms of GmCOL5/13 and GmFT1/2/4/5/6 were synchronized in a day, demonstrating the complicate relationship of CO-FT regulons in soybean leaves. Over-expression of GmCOL2 did not rescue the flowering phenotype of the Arabidopsis co mutant. However, ectopic expression of GmCOL5 did rescue the co mutant phenotype. All GmFTL1 to 6 showed flower-promoting activities in Arabidopsis.

CONCLUSIONS

After three recent rounds of whole genome duplications in the soybean, the paralogous genes of CO-FT regulons showed subfunctionalization through expression divergence. Then, only GmCOL5/13 kept flowering-promoting activities, while GmFTL1 to 6 contributed to flowering control. Additionally, GmCOL5/13 and GmFT1/2/3/4/5/6 showed similar circadian expression profiles. Therefore, our results suggested that GmCOL5/13 and GmFT1/2/3/4/5/6 formed the complicate CO-FT regulons in the photoperiod regulation of flowering time in soybean.

LandCaRe DSS--an interactive decision support system for climate change impact assessment and the analysis of potential agricultural land use adaptation strategies

Decision support to develop viable climate change adaptation strategies for agriculture and regional land use management encompasses a wide range of options and issues. Up to now, only a few suitable tools and methods have existed for farmers and regional stakeholders that support the process of decision-making in this field. The interactive model-based spatial information and decision support system LandCaRe DSS attempts to close the existing methodical gap. This system supports interactive spatial scenario simulations, multi-ensemble and multi-model simulations at the regional scale, as well as the complex impact assessment of potential land use adaptation strategies at the local scale. The system is connected to a local geo-database and via the internet to a climate data server. LandCaRe DSS uses a multitude of scale-specific ecological impact models, which are linked in various ways. At the local scale (farm scale), biophysical models are directly coupled with a farm economy calculator. New or alternative simulation models can easily be added, thanks to the innovative architecture and design of the DSS. Scenario simulations can be conducted with a reasonable amount of effort. The interactive LandCaRe DSS prototype also offers a variety of data analysis and visualisation tools, a help system for users and a farmer information system for climate adaptation in agriculture. This paper presents the theoretical background, the conceptual framework, and the structure and methodology behind LandCaRe DSS. Scenario studies at the regional and local scale for the two Eastern German regions of Uckermark (dry lowlands, 2600 km(2)) and Weißeritz (humid mountain area, 400 km(2)) were conducted in close cooperation with stakeholders to test the functionality of the DSS prototype. The system is gradually being transformed into a web version (http://www.landcare-dss.de) to ensure the broadest possible distribution of LandCaRe DSS to the public. The system will be continuously developed, updated and used in different research projects and as a learning and knowledge-sharing tool for students. The main objective of LandCaRe DSS is to provide information on the complex long-term impacts of climate change and on potential management options for adaptation by answering "what-if" type questions.

Antagonistic roles of SEPALLATA3, FT and FLC genes as targets of the polycomb group gene CURLY LEAF

In Arabidopsis, mutations in the Pc-G gene CURLY LEAF (CLF) give early flowering plants with curled leaves. This phenotype is caused by mis-expression of the floral homeotic gene AGAMOUS (AG) in leaves, so that ag mutations largely suppress the clf phenotype. Here, we identify three mutations that suppress clf despite maintaining high AG expression. We show that the suppressors correspond to mutations in FPA and FT, two genes promoting flowering, and in SEPALLATA3 (SEP3) which encodes a co-factor for AG protein. The suppression of the clf phenotype is correlated with low SEP3 expression in all case and reveals that SEP3 has a role in promoting flowering in addition to its role in controlling floral organ identity. Genetic analysis of clf ft mutants indicates that CLF promotes flowering by reducing expression of FLC, a repressor of flowering. We conclude that SEP3 is the key target mediating the clf phenotype, and that the antagonistic effects of CLF target genes masks a role for CLF in promoting flowering.

Chronopharmacognosy

This study aims to review the concept of biological rhythms in medicinal plants. Dictionariesgenerally define pharmacognosy as the subject of the study of crude drugs of plant and animal origin. The name is derived from the Greek words pharmakon (drug) and gnosis (knowledge). Today pharmacognosy is also defined as the study of physical, chemical, biochemical and biological properties of drugs, drug substances, or potential drugs or drug substances of natural origin, as well as the search for new drugs from natural sources. Also, another important phenomenon to be taken care of in the production of therapeutic compounds in medicinal plants is the use of circardian clock. The circardian clock is studied by chronobiology, which can be defined as a field of science that examines periodic (cyclic) phenomena in living organisms and their adaptation to solar and lunar related rhythms. Thus, it is the scientific study of the effect of time on living systems and of biological rhythms. Also rhythmic oscillations in plants lead to the enormous production of particular compounds in plants at particular time, which may or may not produce any therapeutic effect in humans. Thus, the study of chronobiology and pharmacognosy can be put together as chronopharmacognosy.

Large delay in flowering in continental versus coastal populations of a Mediterranean shrub, Globularia alypum

Globularia alypum is a perennial shrub typical of western Mediterranean thermophilous shrublands. Nine populations of G. alypum located in different localities of Catalonia (NE Spain) were surveyed for flowering phenology. Flower-head buds were present in all the populations in July. Flowering time in the area spans from the late summer-early autumn to the next spring depending on the populations; there are two groups of populations, early and late flowering. Early populations grow mostly in coastal localities and flower from September to November, whereas late flowering populations grow in inland localities and flower from February to April. The flowering order of the populations correlated with minimum temperature of most months except the warmest ones, and correlated with maximum and mean temperatures of the coldest months. Correlations were similar when tested with annual climate. The flowering order also correlated with the thermic interval for most months except the coldest and with the index of continentality. Early populations alone did not present correlations with any variable, whereas late populations alone correlated similarly to all populations together. Flowering order did not correlate with precipitation. Late populations are proposed to be regulated by temperature according to our results whereas early populations could be regulated by timing in precipitation after summer drought, according to published results. We discuss the possibilities of the two flowering patterns, early and late, being due to phenotypic plasticity or to genetic adaptation to local climates. We also discuss the consequences at the plant and ecosystem level of climate warming causing shifts from late to early patterns, a possibility that is likely in the warmest of the late populations if flowering is modulated phenotypically.

CONSTANS and the evolutionary origin of photoperiodic timing of flowering

A network of promoting and inhibiting pathways that respond to environmental and internal signals controls the flowering transition. The outcome of this regulatory network establishes, for any particular plant, the correct time of the year to flower. The photoperiod pathway channels inputs from light, day length, and the circadian clock to promote the floral transition. CONSTANS (CO) is a central regulator of this pathway, triggering the production of the mobile florigen hormone FT (FLOWERING LOCUS T) that induces flower differentiation. Because plant reproductive fitness is directly related to its capacity to flower at a precise time, the photoperiod pathway is present in all known plant species. Recent findings have stretched the evolutionary span of this photophase signal to unicellular algae, which show unexpected conserved characteristics with modern plant photoperiodic responses. In this review, a comparative description of the photoperiodic systems in algae and plants will be presented and a general role for the CO family of transcriptional activators proposed.

The effect of exogenous methyl jasmonate on the flowering time, floral organ morphology, and transcript levels of a group of genes implicated in the development of oilseed rape flowers (Brassica napus L.)

The oilseed rape plant's transition from the vegetative to the reproductive stage is important to its yield. This transition is controlled by a large group of flowering time genes that respond to environmental and endogenous cues. The role of jasmonates in flowering is almost unknown in Brassicaceae, even in the genus Arabidopsis. In this paper, the clear effect of exogenous methyl jasmonate (MeJA) on the flowering time, floral organ morphology, and transcript levels of a group of genes implicated in floral development is shown. In controlled greenhouse experiments, we found that the effect of MeJA depended on both plant genotype and jasmonate dosage. MeJA promoted maximum flowering when it was applied to the cultivars of early flowering types of oilseed rape, such as cultivars Mei-Jian and Fu-You 4. In addition, a concentration of 100 microM resulted in the most number of early open flowers, in comparison with the results obtained for concentrations of 50 and 80 microM. Furthermore, the application of high concentrations of MeJA (100 microM) also produced various kinds of abnormal flowers. Our results demonstrated that the combined actions of the floral identity genes, specifically BnAP1, BnAP2, BnAP3, BnAG1, and BnPI3, as reflected by their respective relative transcript levels, were responsible for causing the different kinds of flower abnormalities previously undescribed in oilseed rape. We expect our assay to be an enriching addition to the body of work that attempts to understand the signaling function of jasmonates in the floral inductive pathway.

Sensitive to freezing6 integrates cellular and environmental inputs to the plant circadian clock

The sensitive to freezing6 (sfr6) mutant of Arabidopsis (Arabidopsis thaliana) is late flowering in long days due to reduced expression of components in the photoperiodic flowering pathway in long-day photoperiods. Microarray analysis of gene expression showed that a circadian clock-associated motif, the evening element, was overrepresented in promoters of genes down-regulated in sfr6 plants. Analysis of leaf movement rhythms found sfr6 plants showed a sucrose (Suc)-dependent long period phenotype; unlike wild-type Arabidopsis, the clock in sfr6 plants did not have a shorter rhythm in the presence of Suc. Other developmental responses to Suc were unaltered in sfr6 plants, suggesting insensitivity to Suc is restricted to the clock. We investigated the effect of sfr6 and Suc upon clock gene expression over 24 h. The sfr6 mutation resulted in reduced expression of the clock components CIRCADIAN CLOCK ASSOCIATED1, GIGANTEA, and TIMING OF CAB1. These changes occurred independently of Suc supplementation. Wild-type plants showed small increases in clock gene expression in the presence of Suc; this response to Suc was reduced in sfr6 plants. This study shows that large changes in level and timing of clock gene expression may have little effect upon clock outputs. Moreover, although Suc influences the period and accuracy of the Arabidopsis clock, it results in relatively minor changes in clock gene expression.

Effects of temperature and light intensity on flowering of barley (Hordeum vulgare L.)

In order to analyse the effects of temperature (9-22 degreesC) and light intensity (170-576 micromol m(-2) s(-1)) on plant development two barley varieties with contrasting seasonal growth habits were included in a series of experiments consisting of controlled environment tests. The effect of constant (18 degrees C) and daily fluctuating (18/16 degrees C) temperature with a long photoperiod was also examined in a set of barley varieties including winter, facultative and spring barleys. Dicktoo with facultative growth habit was more sensitive to unfavourable conditions than Kompolti korai with winter growth habit; the flowering of Dicktoo was significantly delayed by sub- and supra-optimal temperatures and low light intensity accompanied by higher or fluctuating temperatures. The optimal temperature at flowering was also significantly lower for Dicktoo than for Kompolti korai (16.0 degrees C vs. 21.0 degrees C, respectively). Plant development was the fastest when there was no fluctuating environmental factor in the growing conditions and was significantly delayed with application of photo cycle. The addition of thermo cycle to photo cycle had an even stronger delaying effect. Facultative barleys were the most sensitive, followed by winter barleys, while spring barleys the least sensitive to the introduction of thermo cycle.

An AGAMOUS-related MADS-box gene, XAL1 (AGL12), regulates root meristem cell proliferation and flowering transition in Arabidopsis

MADS-box genes are key components of the networks that control the transition to flowering and flower development, but their role in vegetative development is poorly understood. This article shows that the sister gene of the AGAMOUS (AG) clade, AGL12, has an important role in root development as well as in flowering transition. We isolated three mutant alleles for AGL12, which is renamed here as XAANTAL1 (XAL1): Two alleles, xal1-1 and xal1-2, are in Columbia ecotype and xal1-3 is in Landsberg erecta ecotype. All alleles have a short-root phenotype with a smaller meristem, lower rate of cell production, and abnormal root apical meristem organization. Interestingly, we also encountered a significantly longer cell cycle in the strongest xal1 alleles with respect to wild-type plants. Expression analyses confirmed the presence of XAL1 transcripts in roots, particularly in the phloem. Moreover, XAL1beta-glucuronidase expression was specifically up-regulated by auxins in this tissue. In addition, mRNA in situ hybridization showed that XAL1 transcripts were also found in leaves and floral meristems of wild-type plants. This expression correlates with the late-flowering phenotypes of the xal1 mutants grown under long days. Transcript expression analysis suggests that XAL1 is an upstream regulator of SOC, FLOWERING LOCUS T, and LFY. We propose that XAL1 may have similar roles in both root and aerial meristems that could explain the xal1 late-flowering phenotype.

Cold responsive EARLI1 type HyPRPs improve freezing survival of yeast cells and form higher order complexes in plants

Plants have large families of proteins sharing a conserved eight-cysteine-motif (8CM) domain. The biological functions of these proteins are largely unknown. EARLI1 is a cold responsive Arabidopsis gene that encodes a hybrid proline-rich protein (HyPRP) with a three-domain architecture: a putative signal peptide at the N-terminus, a proline-rich domain (PRD) in the middle, and an 8CM domain at the C-terminus. We report here that yeast cells expressing different EARLI1 genes had significantly higher rates of freezing survival than empty-vector transformed controls. Arabidopsis plants with knocked down EARLI1 genes had an increased tendency for freezing-induced cellular damage. EARLI1-GFP fluorescence in transgenic plants and immunoblot analyses using protoplasts suggested cell wall localization for EARLI1 proteins. Immunoblot analyses showed that EARLI1 proteins form higher order complexes in plants, and that the PRD is a soluble and the 8CM an insoluble protein domain. We propose that EARLI1 proteins have a bimodular architecture in which the PRD may interact with the cell wall and the 8CM domain with the plasma membrane to protect the cells during freezing stress.

TaVRT2 represses transcription of the wheat vernalization gene TaVRN1

In wheat, VRN1/TaVRN1 and VRN2/TaVRN2 determine the growth habit and flowering time. In addition, the MADS box transcription factor VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (TaVRT2) is also associated with the vernalization response in a manner similar to TaVRN2. However, the molecular relationship between these three genes and their products is unknown. Using transient expression assays in Nicotiana benthamiana, we show that TaVRT2 acts as a repressor of TaVRN1 transcription. TaVRT2 binds the CArG motif in the TaVRN1 promoter and represses its activity in vivo. In contrast, TaVRN2 does not bind the TaVRN1 promoter and has no direct effect on its activity, but it can enhance the repression effect of TaVRT2. This suggests that a repressor complex regulates the expression of TaVRN1. In winter wheat, TaVRT2, TaVRN2 and TaVRN1 transcripts accumulate in the shoot apical meristem and young leaves, and temporal expression is consistent with TaVRT2 and TaVRN2 being repressors of floral transition, whereas TaVRN1 is an activator. Non-vernalized spring wheat grown under a short-day photoperiod accumulates TaVRT2 and shows a delay in flowering, suggesting that TaVRT2 is regulated independently by photoperiod and low temperature. The data presented suggest that TaVRT2, in association with TaVRN2, represses the transcription of TaVRN1.

Involvement of the histone acetyltransferase AtHAC1 in the regulation of flowering time via repression of FLOWERING LOCUS C in Arabidopsis

Histone acetylation is an important posttranslational modification correlated with gene activation. In Arabidopsis (Arabidopsis thaliana), the histone acetyltransferase AtHAC1 is homologous to animal p300/CREB (cAMP-responsive element-binding protein)-binding proteins, which are the main histone acetyltransferases participating in many physiological processes, including proliferation, differentiation, and apoptosis. The functions of p300/CREB-binding proteins in animals are well characterized, whereas little is known about the roles of AtHAC1 in developmental control in Arabidopsis. Lesions in AtHAC1 caused pleiotropic developmental defects, including delayed flowering, a shortened primary root, and partially reduced fertility. Analysis of the molecular basis of late flowering in hac1 mutants showed that the hac1 plants respond normally to day length, gibberellic acid treatment, and vernalization. Furthermore, the expression level of the flowering repressor FLOWERING LOCUS C (FLC) is increased in hac1 mutants, indicating that the late-flowering phenotype of hac1 mutants is mediated by FLC. Since histone acetylation is usually associated with the activation of gene expression, histone modifications of FLC chromatin are not affected by mutations in HAC1 and expression levels of all known autonomous pathway genes are unchanged in hac1 plants, we propose that HAC1 affects flowering time by epigenetic modification of factors upstream of FLC.

Activation of zoosporogenesis-specific genes in Phytophthora infestans involves a 7-nucleotide promoter motif and cold-induced membrane rigidity

Infections of plants by the oomycete Phytophthora infestans typically result from zoospores, which develop from sporangia at cold temperatures. To help understand the relevant cold-induced signaling pathway, factors regulating the transcription of the zoosporogenesis-specific NIF (nuclear LIM-interactor-interacting factor) gene family were examined. Sequences required for inducing PinifC3 were identified by analyzing truncated and mutated promoters using the beta-glucuronidase reporter in stable transformants. A 7-nucleotide (nt) sequence located 139 bases upstream of the major transcription start point (GGACGAG) proved essential for the induction of PinifC3 when sporangia were shifted from ambient to cold temperatures. The motif, named the cold box, also conferred cold inducibility to a promoter normally activated only during sexual development. An identical motif was detected in the two other zoosporogenesis-specific NIF genes from P. infestans and three Phytophthora sojae orthologues, and a closely related sequence was found in Phytophthora ramorum orthologues. The 7-nt motif was also found in the promoters of other zoosporogenesis-induced genes. The presence of a cold box-interacting protein in nuclear extracts of P. infestans sporangia was demonstrated using electrophoretic mobility shift assays. Furthermore, zoospore release and cold box-regulated transcription were stimulated by the membrane rigidizer dimethyl sulfoxide and inhibited by the membrane fluidizer benzyl alcohol. The data therefore delineate a pathway in which sporangia perceive cold temperatures through membrane rigidity, which activates signals that drive both zoosporogenesis and cold-box-mediated transcription.

Rapid differentiation of experimental populations of wheat for heading time in response to local climatic conditions

BACKGROUND AND AIMS

Dynamic management (DM) of genetic resources aims at maintaining genetic variability between different populations evolving under natural selection in contrasting environments. In 1984, this strategy was applied in a pilot experiment on wheat (Triticum aestivum). Spatio-temporal evolution of earliness and its components (partial vernalization sensitivity, daylength sensitivity and earliness per se that determines flowering time independently of environmental stimuli) was investigated in this multisite and long-term experiment.

METHODS

Heading time of six populations from the tenth generation was evaluated under different vernalization and photoperiodic conditions.

KEY RESULTS

Although temporal evolution during ten generations was not significant, populations of generation 10 were genetically differentiated according to a north-south latitudinal trend for two components out of three: partial vernalization sensitivity and narrow-sense earliness.

CONCLUSIONS

It is concluded that local climatic conditions greatly influenced the evolution of population earliness, thus being a major factor of differentiation in the DM system. Accordingly, a substantial proportion (approximately 25 %) of genetic variance was distributed among populations, suggesting that diversity was on average conserved during evolution but was differently distributed by natural selection (and possibly drift). Earliness is a complex trait and each genetic factor is controlled by multiple homeoalleles; the next step will be to look for spatial divergence in allele frequencies.

Increased ascorbate content delays flowering in long-day grown Arabidopsis thaliana (L.) Heynh

Flowering requires the integration of different inductive stimuli, including light, temperature and hormones. In an attempt to assess whether ascorbate (ASC) could contribute to the control of flowering time, we analyzed the effects of increased ASC content on the transition to the reproductive stage in the facultative long-day plant Arabidopsis thaliana. ASC content was increased by spraying leaves with the ASC precursor L-galactono-gamma-lactone. Our data show that increased ASC content did not affect vegetative growth, whereas a significant delay (5 days in average) in flower production occurred in ASC-overproducing plants. Higher ASC availability resulted in delayed expression of LEAFY (LFY), the gene encoding for a key transcription factor integrating different flowering-inductive pathways. On the contrary, spraying with gibberellin under the same condition caused both early LFY expression and early flowering. The possible role of ASC in the transition to the reproductive stage is discussed.

Characterization of the vernalization response in Lolium perenne by a cDNA microarray approach

Many plant species including temperate grasses require vernalization in order to flower. Vernalization is the process of promotion of flowering after exposure to prolonged periods of cold. To investigate the vernalization response in monocots, the expression patterns of about 1,500 unique genes of Lolium perenne were analyzed by a cDNA microarray approach, at different time points after transfer of plants to low temperatures. Vernalization of L. perenne takes around 80 d and, therefore, the plants were incubated at low temperatures for at least 12 weeks. A total of 70 cold-responsive genes were identified that are either up- or down-regulated with a minimal 2-fold difference compared with the common reference. The majority of these genes show a very rapid response to the cold treatment, indicating that their expression is affected by the cold stress and, therefore, these genes are not likely to be involved in the flowering process. Based on hierarchical clustering, one gene could be identified that is down-regulated towards the end of the cold period and, in addition, a few genes have been found that are up-regulated in the last weeks of the cold treatment and, hence, are putative candidates for genes involved in the vernalization response. Three of the up-regulated genes are homologous to members of the MADS box, CONSTANS-like and JUMONJI families of transcription factors, respectively. The latter two are novel genes not connected previously to vernalization-induced flowering. Furthermore, members of the JUMONJI family of transcription factors have been shown to be involved in chromatin remodeling, suggesting that this molecular mechanism, as in Arabidopsis, plays a role in the regulation of the vernalization response in monocots.

Overexpression of COL9, a CONSTANS-LIKE gene, delays flowering by reducing expression of CO and FT in Arabidopsis thaliana

CONSTANS (CO) is an important floral regulator in the photoperiod pathway, integrating the circadian clock and light signal into a control for flowering time. It is known that CO promotes flowering in Arabidopsis under long-day conditions. CONSTANS-LIKE 9 (COL9) is a member of the CONSTANS-LIKE gene family, encoding a nuclear protein. The expression of COL9 is regulated by the circadian clock in the photoperiod pathway and is detected in various organs. Unexpectedly, overexpression of COL9 in transgenic Arabidopsis resulted in delayed flowering, while co-suppression lines and a transferred DNA (T-DNA) knockout line showed earlier flowering under long-day conditions. Overexpression of COL9 did not enhance the late-flowering phenotype in a co mutant background. Double overexpressors produced by overexpression of CO in COL9 transgenic lines showed an early flowering phenotype similar to single CO overexpressors. The pattern of oscillation of a number of circadian-associated genes remained unchanged in the COL9 transgenic lines. Compared with wild-type plants, the abundance of CO and FLOWERING LOCUS T (FT) mRNA was reduced in the COL9 overexpression lines. Our results indicate that COL9 is involved in regulation of flowering time by repressing the expression of CO, concomitantly reducing the expression of FT and delaying floral transition.

Identifying Eucalyptus expressed sequence tags related to Arabidopsis flowering-time pathway genes

Flowering initiation depends on the balanced expression of a complex network of genes that is regulated by both endogenous and environmental factors. The timing of the initiation of flowering is crucial for the reproductive success of plants; therefore, they have developed conserved molecular mechanisms to integrate both environmental and endogenous cues to regulate flowering time precisely. Extensive advances in plant biology are possible now that the complete genome sequences of flowering plants is available and plant genomes can be comprehensively compared. Thus, association studies are emerging as powerful tools for the functional identification of genes involved on the regulation of flowering pathways. In this paper we report the results of our search in the Eucalyptus Genome Sequencing Project Consortium (FORESTS) database for expressed sequence tags (ESTs) showing sequence homology with known elements of flowering-time pathways. We have searched the 33,080 sequence clusters in the FORESTS database and identified Eucalyptus sequences that codify putative conserved elements of the autonomous, vernalization-, photoperiod response- and gibberellic acid-controlled flowering-time pathways. Additionally, we have characterized in silico ten putative members of the Eucalyptus homologs to the Arabidopsis CONSTANS family of transcription factors.

Delay in flowering and increase in biomass of transgenic tobacco expressing the Arabidopsis floral repressor gene FLOWERING LOCUS C

FLOWERING LOCUS C (FLC), a gene from Arabidopsis thaliana (L.) Heynh. that acts as a flowering repressor, was expressed in tobacco (Nicotiana tabacum L. 'Samsun'). Five putative transgenic lines were selected and examined for the presence of FLC. Genomic DNA and total RNA were isolated from the Leaves and used for polymerase chain reaction (PCR) and RNA blot analysis, respectively. Both DNA and RNA tests confirmed the integration and transcription of FLC in all five Lines and their T1 progenies. Transgenic plants in one Line showed an average of 36 d delay in flowering time compared to control plants, and the overall mean for all lines was 14 d. Transgenic plants also displayed increased leaf size and biomass yield and reduced height at flowering time. It is important to note that the delay in flowering might have been caused by a slower rate of leaf initiation (i.e. nodes/day) rather than by a change in the flowering mechanism itself.

The wheat TaGI1, involved in photoperiodic flowering, encodes an Arabidopsis GI ortholog

Wheat (Triticum aestivum L.) is an important crop and requires long day and short night to flower. To study the molecular mechanism of photoperiodic regulation of flowering in this species, we isolated a wheat TaGI1 gene, an ortholog of GIGANTEA (GI) in Arabidopsis. RNA blot hybridization revealed that TaGI1 is expressed in leaves in a rhythmic manner under long day and short day conditions and its rhythmic expression is regulated by photoperiods and circadian clocks. Further study demonstrated that the TaGI1 rhythmic expression in the leaves of seedlings is initiated by photoperiods, implying that TaGI1 does not show circadian regulation until after being entrained in a light/dark cycle. Interestingly, TaGI1 mRNA was detected in adaxial epidermal cells right above the vascular bundles of leaves, suggesting that the localization of TaGI1 transcripts in leaves may function to regulate flowering in response to photoperiods. Since overexpression of TaGI1 altered flowering time in wild type and complemented the gi mutant in Arabidopsis, it confirmed that TaGI1 is an ortholog of GI in Arabidopsis.

Differential regulation of FLOWERING LOCUS C expression by vernalization in cabbage and Arabidopsis

Vernalization is required to induce flowering in cabbage (Brassica oleracea var Capitata L.). Since FLOWERING LOCUS C (FLC) was identified as a major repressor of flowering in the vernalization pathway in Arabidopsis (Arabidopsis thaliana), two homologs of AtFLC, BoFLC3-2 and BoFLC4-1, were isolated from cabbage to investigate the molecular mechanism of vernalization in cabbage flowering. In addition to the sequence homology, the genomic organization of cabbage FLC is similar to that of AtFLC, except that BoFLC has a relatively smaller intron 1 compared to that of AtFLC. A vernalization-mediated decrease in FLC transcript level was correlated with an increase in FT transcript level in the apex of cabbage. This observation is in agreement with the down-regulation of FT by FLC in Arabidopsis. Yet, unlike that in Arabidopsis, the accumulation of cabbage FLC transcript decreased after cold treatment of leafy plants but not imbibed seeds, which is consistent with the promotion of cabbage flowering by vernalizing adult plants rather than seeds. To further dissect the different regulation of FLC expression between seed-vernalization-responsive species (e.g. Arabidopsis) and plant-vernalization-responsive species (e.g. cabbage), the pBoFLC4-1BoFLC4-1GUS construct was introduced into Arabidopsis to examine its vernalization response. Down-regulation of the BoFLC4-1GUS construct by seed vernalization was unstable and incomplete; in addition, the expression of BoFLC4-1GUS was not suppressed by vernalization of transgenic rosette-stage Arabidopsis plants. We propose a hypothesis to illustrate the distinct mechanism by which vernalization regulates the expression of FLC in cabbage and Arabidopsis.

Flowering time control: gene network modelling and the link to quantitative genetics

Flowering is a key stage in plant development that initiates grain production and is vulnerable to stress. The genes controlling flowering time in the model plant Arabidopsis thaliana are reviewed. Interactions between these genes have been described previously by qualitative network diagrams. We mathematically relate environmentally dependent transcription, RNA processing, translation, and protein–protein interaction rates to resultant phenotypes. We have developed models (reported elsewhere) based on these concepts that simulate flowering times for novel A. thaliana genotype–environment combinations. Here we draw 12 contrasts between genetic network (GN) models of this type and quantitative genetics (QG), showing that both have equal contributions to make to an ideal theory. Physiological dominance and additivity are examined as emergent properties in the context of feed-forwards networks, an instance of which is the signal-integration portion of the A. thaliana flowering time network. Additivity is seen to be a complex, multi-gene property with contributions from mass balance in transcript production, the feed-forwards structure itself, and downstream promoter reaction thermodynamics. Higher level emergent properties are exemplified by critical short daylength (CSDL), which we relate to gene expression dynamics in rice (Oryza sativa). Next to be discussed are synergies between QG and GN relating to the quantitative trait locus (QTL) mapping of model coefficients. This suggests a new verification test useful in GN model development and in identifying needed updates to existing crop models. Finally, the utility of simple models is evinced by 80 years of QG theory and mathematical ecology.

Photoperiod regulates flower meristem development in Arabidopsis thaliana

Photoperiod has been known to regulate flowering time in many plant species. In Arabidopsis, genes in the long day (LD) pathway detect photoperiod and promote flowering under LD. It was previously reported that clavata2 (clv2) mutants grown under short day (SD) conditions showed suppression of the flower meristem defects, namely the accumulation of stem cells and the resulting production of extra floral organs. Detailed analysis of this phenomenon presented here demonstrates that the suppression is a true photoperiodic response mediated by the inactivation of the LD pathway under SD. Inactivation of the LD pathway was sufficient to suppress the clv2 defects under LD, and activation of the LD pathway under SD conditions restored clv2 phenotypes. These results reveal a novel role of photoperiod in flower meristem development in Arabidopsis. Flower meristem defects of clv1 and clv3 mutants are also suppressed under SD, and 35S:CO enhanced the defects of clv3, indicating that the LD pathway works independently from the CLV genes. A model is proposed to explain the interactions between photoperiod and the CLV genes.

Changes in the geometry of the apical meristem and concomitant changes in cell wall properties during photoperiodic induction of flowering in Chenopodium rubrum

•  A putative role for local forces at the surface of the apical meristem for plant organogenesis has been postulated in various studies. To correlate changes in morphogenesis to altered local forces, we followed the geometry of the apical meristem during photoperiodic flower induction in Chenopodium rubrum. •  The shape of the apical meristem was determined using cryo-scanning electron microscopy. Cell wall properties on the surface of the dome were visualized using uplight polarization microscopy. •  A subtle depression at the summit of the apical dome, typical for the vegetative state, became rounded during the early phase of flower induction. The observed changes were quantified as an increase in the ratio of height to diameter of the dome. In parallel, the properties of cell walls on the surface of the dome changed. •  The changes in geometry of the apical meristem were attributed to water movement in the meristem paralleled by a change in cell wall properties at the top of the dome. The results support the hypothesis that local changes in surface tension precede initiation of organ primordia.

Cell wall invertase expression at the apical meristem alters floral, architectural, and reproductive traits in Arabidopsis thaliana

Resource allocation is a major determinant of plant fitness and is influenced by external as well as internal stimuli. We have investigated the effect of cell wall invertase activity on the transition from vegetative to reproductive growth, inflorescence architecture, and reproductive output, i.e. seed production, in the model plant Arabidopsis thaliana by expressing a cell wall invertase under a meristem-specific promoter. Increased cell wall invertase activity causes accelerated flowering and an increase in seed yield by nearly 30%. This increase is caused by an elevation of the number of siliques, which results from enhanced branching of the inflorescence. On the contrary, as cytosolic enzyme, the invertase causes delayed flowering, reduced seed yield, and branching. This demonstrates that invertases not only are important in determining sink strength of storage organs but also play a role in regulating developmental processes.

Environmental and genetic effects on flowering differences between northern and southern populations of Arabidopsis lyrata (Brassicaceae)

Arabidopsis lyrata (Brassicaceae) is a close outcrossing relative of A. thaliana. We examine flowering time variation of northern and southern A. lyrata populations in controlled environmental conditions, in a common garden experiment with A. thaliana, and in the field. Southern populations of A. lyrata flowered earlier than northern ones in all environmental conditions. Individuals from southern populations were more likely to flower in short days (14 h light) than northern ones, and all populations had a higher probability of flowering and flowered more rapidly in long days (20 h). The interaction of population and day length significantly affected flowering probability, and flowering time in one of two comparisons. The common garden experiment demonstrated differences between populations in the response to seed cold treatment, but growth chamber experiments showed no vernalization effect after 4 wk of rosette cold treatment. In a field population in Norway, a high proportion of the plants flowered in each year of the study. The plants progressed to flowering more rapidly in the field and common garden than in the growth chamber. The genetic basis of these flowering time differences here can be further studied using A. thaliana genetic tools.

Factors Affecting Quality and Postharvest Properties of Vegetables: Integration of Water Relations and Metabolism

Growing of vegetables in the field, harvesting, handling in the packing house and storage are events in the lifetime of vegetables that are analysed from the point of view of the complex series of physiological transitions taking place in each of these events. Water is the major factor limiting plant metabolism and plants have developed fascinating mechanisms to cope with this limiting factor. Therefore, water relations (water, pressure and osmotic potential) are used as criteria for discussing plant stress physiology aspects such as osmotic, elastic adjustment and cold acclimation, as well as mechanical stress when the vegetable is harvested and during handling in the packing house. Consequences for the storage potential and quality of the vegetable are discussed. After harvesting, the postharvest cell has the ability to complete a complex series of physiological transitions that will influence vegetable quality andfurther processing operations. Metabolic changes in the cytosol, cell membrane and cell wall are described.

UNIFLORA, a pivotal gene that regulates floral transition and meristem identity in tomato (Lycopersicon esculentum)

•  Flowering of uniflora (uf), a tomato (Lycopersicon esculentum) mutant which consistently produces solitary flowers instead of inflorescences, is late and highly asynchronous in winter. This puzzling behaviour prompted us to further investigate flowering regulation in this mutant to improve our understanding of UNIFLORA gene function. •  Growing plants under different daylengths and light intensities revealed that flowering time in uf is dependent on daily light energy integral. Transferring plants from low to high light energy integrals at different times after sowing showed that the light-conditions effect was stage dependent, suggesting that interactions between light energy integrals and endogenous regulatory pathways affect meristem sensitivity to flowering signals. •  Carbohydrate analyses suggested that one of these signals could be sucrose, but other interacting factors are probably generated by the root system, as indicated by grafting experiments. •  The UNIFLORA gene thus appears to have a dual role in tomato: floral transition regulation and the maintenance of inflorescence meristem identity.

Genotype-Environment Interactions at Quantitative Trait Loci Affecting Inflorescence Development in Arabidopsis thaliana

Phenotypic plasticity and genotype-environment interactions (GEI) play a prominent role in plant morphological diversity and in the potential functional capacities of plant life-history traits. The genetic basis of plasticity and GEI, however, is poorly understood in most organisms. In this report, inflorescence development patterns in Arabidopsis thaliana were examined under different, ecologically relevant photoperiod environments for two recombinant inbred mapping populations (Ler × Col and Cvi × Ler) using a combination of quantitative genetics and quantitative trait locus (QTL) mapping. Plasticity and GEI were regularly observed for the majority of 13 inflorescence traits. These observations can be attributable (at least partly) to variable effects of specific QTL. Pooled across traits, 12/44 (27.3%) and 32/62 (51.6%) of QTL exhibited significant QTL × environment interactions in the Ler × Col and Cvi × Ler lines, respectively. These interactions were attributable to changes in magnitude of effect of QTL more often than to changes in rank order (sign) of effect. Multiple QTL × environment interactions (in Cvi × Ler) clustered in two genomic regions on chromosomes 1 and 5, indicating a disproportionate contribution of these regions to the phenotypic patterns observed. High-resolution mapping will be necessary to distinguish between the alternative explanations of pleiotropy and tight linkage among multiple genes.

Reciprocal control of flowering time by OsSOC1 in transgenic Arabidopsis and by FLC in transgenic rice

In a screen for MADS box genes which activate and/or repress flowering in rice, we identified a gene encoding a MADS domain protein (OsSOC1) related to the Arabidopsis gene AtSOC1. AtSOC1 and OsSOC1 show a 97% amino acid similarity in their MADS domain. The rice gene contains a large first intron of 27.6 kb compared to the 1 kb intron in Arabidopsis. OsSOC1 is located on top of the short arm of chromosome 3, tightly linked to the heading date locus, Hd9. OsSOC1 is expressed in vegetative tissues, and expression is elevated at the time of floral initiation, 40-50 days after sowing, and remains uniformly high thereafter, similar to the expression pattern of AtSOC1. The constitutive expression of OsSOC1 in Arabidopsis results in early flowering, suggesting that the rice gene is a functional equivalent of AtSOC1. We were not able to identify FLC-like sequences in the rice genome; however, we show that ectopic expression of the Arabidopsis FLC delays flowering in rice, and the up-regulation of OsSOC1 at the onset of flowering initiation is delayed in the AtFLC transgenic lines. The reciprocal recognition and flowering time effects of genes introduced into either Arabidopsis or rice suggest that some components of the flowering pathways may be shared. This points to a potential application in the manipulation of flowering time in cereals using well characterized Arabidopsis genes.

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.

Arabidopsis TERMINAL FLOWER 2 gene encodes a heterochromatin protein 1 homolog and represses both FLOWERING LOCUS T to regulate flowering time and several floral homeotic genes

Floral transition should be strictly regulated because it is one of the most critical developmental processes in plants. Arabidopsis terminal flower 2 (tfl2) mutants show an early-flowering phenotype that is relatively insensitive to photoperiod, as well as several other pleiotropic phenotypes. We found that the early flowering of tfl2 is caused mainly by ectopic expression of the FLOWERING LOCUS T (FT) gene, a floral pathway integrator. Molecular cloning of TFL2 showed that it encodes a protein with homology to heterochromatin protein 1 (HP1) of animals and Swi6 of fission yeast. TFL2 protein localizes in subnuclear foci and expression of the TFL2 gene complemented yeast swi6(-) mutants. These results suggested that TFL2 might function as an HP1 in Arabidopsis: Gene expression analyses using DNA microarrays, however, did not show an increase in the expression of heterochromatin genes in tfl2 mutants but instead showed the upregulation of the floral homeotic genes APETALA3, PISTILLATA, AGAMOUS and SEPALLATA3. The pleiotropic phenotype of the tfl2 mutant could reflect the fact that TFL2 represses the expression of multiple genes. Our results demonstrate that despite its homology to HP1, TFL2 is involved in the repression of specific euchromatin genes and not heterochromatin genes in Arabidopsis.

Analysis of the Arabidopsis MADS AFFECTING FLOWERING gene family: MAF2 prevents vernalization by short periods of cold

The Arabidopsis FLOWERING LOCUS C (FLC) gene is a key floral repressor in the maintenance of a vernalization response. In vernalization-sensitive genetic backgrounds, FLC levels are high, and they decline after exposure to long cold periods. Four FLC paralogs (MAF2 [MADS AFFECTING FLOWERING2] to MAF5) are arranged in a tandem array on the bottom of Arabidopsis chromosome V. We used a reverse genetics approach to analyze their functions. Loss-of-function and gain-of-function studies indicate that MAF2 acts as a floral repressor. In particular, maf2 mutant plants display a pronounced vernalization response when subjected to relatively short cold periods, which are insufficient to elicit a strong flowering response in the wild type, despite producing a large reduction in FLC levels. MAF2 expression is less sensitive to vernalization than that of FLC, and its repressor activity is exerted independently or downstream of FLC transcription. Thus, MAF2 can prevent premature vernalization in response to brief cold spells. Overexpression of MAF3 or MAF4 produces alterations in flowering time that suggest that these genes also act as floral repressors and might contribute to the maintenance of a vernalization requirement. However, the final gene in the cluster, MAF5, is upregulated by vernalization. Therefore, MAF5 could play an opposite role to FLC in the vernalization response.

Low temperature inhibits RNA silencing-mediated defence by the control of siRNA generation

Temperature dramatically affects plant-virus interactions. Outbreaks of virus diseases are frequently associated with low temperature, while at high temperature viral symptoms are often attenuated (heat masking) and plants rapidly recover from virus diseases. However, the underlying mechanisms of these well-known observations are not yet understood. RNA silencing is a conserved defence system of eukaryotic cells, which operates against molecular parasites including viruses and transgenes. Here we show that at low temperature both virus and transgene triggered RNA silencing are inhibited. Therefore, in cold, plants become more susceptible to viruses, and RNA silencing-based phenotypes of transgenic plants are lost. Consistently, the levels of virus- and transgene-derived small (21-26 nucleotide) interfering (si) RNAs-the central molecules of RNA silencing-mediated defence pathways-are dramatically reduced at low temperature. In contrast, RNA silencing was activated and the amount of siRNAs gradually increased with rising temperature. However, temperature does not influence the accumulation of micro (mi) RNAs, which play a role in developmental regulation, suggesting that the two classes of small (si and mi) RNAs are generated by different nuclease complexes.

Hd3a, a rice ortholog of the Arabidopsis FT gene, promotes transition to flowering downstream of Hd1 under short-day conditions

Heading date 3a (Hd3a) has been detected as a heading-date-related quantitative trait locus in a cross between rice cultivars Nipponbare and Kasalath. A previous study revealed that the Kasalath allele of Hd3a promotes heading under short-day (SD) conditions. High-resolution linkage mapping located the Hd3a locus in a approximately 20-kb genomic region. In this region, we found a candidate gene that shows high similarity to the FLOWERING LOCUS T (FT) gene, which promotes flowering in Arabidopsis: Introduction of the gene caused an early-heading phenotype in rice. The transcript levels of Hd3a were increased under SD conditions. The rice Heading date 1 (Hd1) gene, a homolog of CONSTANS (CO), has been shown to promote heading under SD conditions. By expression analysis, we showed that the amount of Hd3a mRNA is up-regulated by Hd1 under SD conditions, suggesting that Hd3a promotes heading under the control of Hd1. These results indicate that Hd3a encodes a protein closely related to Arabidopsis FT and that the function and regulatory relationship with Hd1 and CO, respectively, of Hd3a and FT are conserved between rice (an SD plant) and Arabidopsis (a long-day plant).