Cis-regulatory Changes at FLOWERING LOCUS T Mediate Natural Variation in Flowering Responses of Arabidopsis thaliana

Flowering time, a critical adaptive trait, is modulated by several environmental cues. These external signals converge on a small set of genes that in turn mediate the flowering response. Mutant analysis and subsequent molecular studies have revealed that one of these integrator genes, FLOWERING LOCUS T (FT), responds to photoperiod and temperature cues, two environmental parameters that greatly influence flowering time. As the central player in the transition to flowering, the protein coding sequence of FT and its function are highly conserved across species. Using QTL mapping with a new advanced intercross-recombinant inbred line (AI-RIL) population, we show that a QTL tightly linked to FT contributes to natural variation in the flowering response to the combined effects of photoperiod and ambient temperature. Using heterogeneous inbred families (HIF) and introgression lines, we fine map the QTL to a 6.7 kb fragment in the FT promoter. We confirm by quantitative complementation that FT has differential activity in the two parental strains. Further support for FT underlying the QTL comes from a new approach, quantitative knockdown with artificial microRNAs (amiRNAs). Consistent with the causal sequence polymorphism being in the promoter, we find that the QTL affects FT expression. Taken together, these results indicate that allelic variation at pathway integrator genes such as FT can underlie phenotypic variability and that this may be achieved through cis-regulatory changes.MOLECULAR analysis of the phenotypic variation in life history traits is key to understanding how plants evolve in diverse natural environments. Among such traits, flowering time is critical for the reproductive success of the plant and is highly variable among natural Arabidopsis thaliana strains, providing an attractive paradigm for studying adaptive evolution (Johanson et al. 2000; Hagenblad and Nordborg 2002; Stinchcombe et al. 2004; Lempe et al. 2005; Shindo et al. 2005; Werner et al. 2005a). Two major environmental parameters that modulate flowering time are light and temperature (Koornneef et al. 1998). Temperature and light conditions vary substantially within the geographical range of A. thaliana, and natural populations presumably need to adapt to the local environment to ensure reproductive success. Flowering in A. thaliana is generally accelerated by long photoperiods, vernalization (exposure to winter-like conditions), and elevated ambient temperatures (Bäurle and Dean 2006). All these cues favor flowering of A. thaliana during spring or early summer, although the contribution from each individual cue and the interactions among them vary depending on the local environmental conditions (Wilczek et al. 2009).Flowering time is controlled through several genetic cascades that converge on a set of integrator genes including FLOWERING LOCUS T (FT), which encodes a protein that is highly conserved in flowering plants (Kardailsky et al. 1999; Kobayashi et al. 1999; Ahn et al. 2006). FT and its homologs are very likely an integral part of the mobile signal (florigen) that is produced in leaves and travels to the shoot apex to induce flowering (Abe et al. 2005; Wigge et al. 2005; Lifschitz et al. 2006; Corbesier et al. 2007; Jaeger and Wigge 2007; Lin et al. 2007; Mathieu et al. 2007; Tamaki et al. 2007; Notaguchi et al. 2008). In A. thaliana, FT expression is controlled by photoperiod, vernalization, and ambient growth temperature. Photoperiod in conjunction with the circadian clock promotes daily oscillations in FT RNA levels, which are greatly elevated at the end of long days. The central role of FT in determining the timing of flowering appears to be conserved in many species, making FT an attractive target for altering flowering time in cereals and other plants of economic importance (recently reviewed by Kobayashi and Weigel 2007; Turck et al. 2008).Wild strains of A. thaliana show extensive variation in flowering time and much of this is due to variation in the activity of the floral repressor FLOWERING LOCUS C (FLC). While some of this variation maps to FLC itself, much of it is due to differential activity at the epistatically acting FRIGIDA (FRI) locus (Michaels and Amasino 1999; Sheldon et al. 1999; Johanson et al. 2000; Michaels et al. 2003; Lempe et al. 2005; Shindo et al. 2005, 2006). Flowering is typically substantially delayed when the FRI/FLC system is active, unless these plants are first vernalized. However, FRI and FLC do not explain all of the flowering time variation seen in wild strains, and functionally divergent alleles of several additional flowering regulators, including CRYPTOCHROME 2 (CRY2), HUA2, FLOWERING LOCUS M (FLM), PHYTOCHROME C (PHYC), and PHYTOCHROME D (PHYD), have been identified in different strains of A. thaliana (Aukerman et al. 1997; Alonso-Blanco et al. 1998; El-Assal et al. 2001; Werner et al. 2005b; Balasubramanian et al. 2006a; Wang et al. 2007). Finally, there are many genotype-by-environment interactions that dramatically affect the contribution of a specific locus to the overall phenotype.The study of natural variation in A. thaliana has been greatly facilitated through the use of recombinant inbred line (RIL) populations (Koornneef et al. 2004). We have recently established two advanced intercross (AI)-RIL sets, in which the genetic map is greatly expanded, allowing for high-resolution QTL mapping (Balasubramanian et al. 2009). Here we use one of the new AI-RIL populations along with an independent F₂ population to identify the molecular basis of a light and temperature-sensitive flowering time QTL that mapped to the promoter of the FT gene. We show that FT is likely the causal gene for variation in light and temperature-sensitive flowering. Our results, in combination with those from other species, suggest that cis-regulatory variation rather than structural variation at FT contributes to phenotypic variation in natural populations.     

Exploiting Natural Variation of Secondary Metabolism Identifies a Gene Controlling the Glycosylation Diversity of Dihydroxybenzoic Acids in Arabidopsis thaliana

Plant secondary metabolism is an active research area because of the unique and important roles the specialized metabolites have in the interaction of plants with their biotic and abiotic environment, the diversity and complexity of the compounds and their importance to human medicine. Thousands of natural accessions of Arabidopsis thaliana characterized with increasing genomic precision are available, providing new opportunities to explore the biochemical and genetic mechanisms affecting variation in secondary metabolism within this model species. In this study, we focused on four aromatic metabolites that were differentially accumulated among 96 Arabidopsis natural accessions as revealed by leaf metabolic profiling. Using UV, mass spectrometry, and NMR data, we identified these four compounds as different dihydroxybenzoic acid (DHBA) glycosides, namely 2,5-dihydroxybenzoic acid (gentisic acid) 5-O-β-D-glucoside, 2,3-dihydroxybenzoic acid 3-O-β-D-glucoside, 2,5-dihydroxybenzoic acid 5-O-β-D-xyloside, and 2,3-dihydroxybenzoic acid 3-O-β-D-xyloside. Quantitative trait locus (QTL) mapping using recombinant inbred lines generated from C24 and Col-0 revealed a major-effect QTL controlling the relative proportion of xylosides vs. glucosides. Association mapping identified markers linked to a gene encoding a UDP glycosyltransferase gene. Analysis of Transfer DNA (T-DNA) knockout lines verified that this gene is required for DHBA xylosylation in planta and recombinant protein was able to xylosylate DHBA in vitro. This study demonstrates that exploiting natural variation of secondary metabolism is a powerful approach for gene function discovery.     

Natural Variation in Stomatal Responses to Environmental Changes among Arabidopsis thaliana Ecotypes

Stomata are small pores surrounded by guard cells that regulate gas exchange between plants and the atmosphere. Guard cells integrate multiple environmental signals and control the aperture width to ensure appropriate stomatal function for plant survival. Leaf temperature can be used as an indirect indicator of stomatal conductance to environmental signals. In this study, leaf thermal imaging of 374 Arabidopsis ecotypes was performed to assess their stomatal responses to changes in environmental CO2 concentrations. We identified three ecotypes, Köln (Kl-4), Gabelstein (Ga-0), and Chisdra (Chi-1), that have particularly low responsiveness to changes in CO2 concentrations. We next investigated stomatal responses to other environmental signals in these selected ecotypes, with Col-0 as the reference. The stomatal responses to light were also reduced in the three selected ecotypes when compared with Col-0. In contrast, their stomatal responses to changes in humidity were similar to those of Col-0. Of note, the responses to abscisic acid, a plant hormone involved in the adaptation of plants to reduced water availability, were not entirely consistent with the responses to humidity. This study demonstrates that the stomatal responses to CO2 and light share closely associated signaling mechanisms that are not generally correlated with humidity signaling pathways in these ecotypes. The results might reflect differences between ecotypes in intrinsic response mechanisms to environmental signals.     

Modulation of Ambient Temperature-Dependent Flowering in Arabidopsis thaliana by Natural Variation of FLOWERING LOCUS M

Plants integrate seasonal cues such as temperature and day length to optimally adjust their flowering time to the environment. Compared to the control of flowering before and after winter by the vernalization and day length pathways, mechanisms that delay or promote flowering during a transient cool or warm period, especially during spring, are less well understood. Due to global warming, understanding this ambient temperature pathway has gained increasing importance. In Arabidopsis thaliana, FLOWERING LOCUS M (FLM) is a critical flowering regulator of the ambient temperature pathway. FLM is alternatively spliced in a temperature-dependent manner and the two predominant splice variants, FLM-ß and FLM-δ, can repress and activate flowering in the genetic background of the A. thaliana reference accession Columbia-0. The relevance of this regulatory mechanism for the environmental adaptation across the entire range of the species is, however, unknown. Here, we identify insertion polymorphisms in the first intron of FLM as causative for accelerated flowering in many natural A. thaliana accessions, especially in cool (15°C) temperatures. We present evidence for a potential adaptive role of this structural variation and link it specifically to changes in the abundance of FLM-ß. Our results may allow predicting flowering in response to ambient temperatures in the Brassicaceae.     

Gene Regulatory Variation Mediates Flowering Responses to Vernalization along an Altitudinal Gradient in Arabidopsis

Steep environmental gradients provide ideal settings for studies of potentially adaptive phenotypic and genetic variation in plants. The accurate timing of flowering is crucial for reproductive success and is regulated by several pathways, including the vernalization pathway. Among the numerous genes known to enable flowering in response to vernalization, the most prominent is FLOWERING LOCUS C (FLC). FLC and other genes of the vernalization pathway vary extensively among natural populations and are thus candidates for the adaptation of flowering time to environmental gradients such as altitude. We used 15 natural Arabidopsis (Arabidopsis thaliana) genotypes originating from an altitudinal gradient (800–2,700 m above sea level) in the Swiss Alps to test whether flowering time correlated with altitude under different vernalization scenarios. Additionally, we measured the expression of 12 genes of the vernalization pathway and its downstream targets. Flowering time correlated with altitude in a nonlinear manner for vernalized plants. Flowering time could be explained by the expression and regulation of the vernalization pathway, most notably by AGAMOUS LIKE19 (AGL19), FLOWERING LOCUS T (FT), and FLC. The expression of AGL19, FT, and VERNALIZATION INSENSITIVE3 was associated with altitude, and the regulation of MADS AFFECTING FLOWERING2 (MAF2) and MAF3 differed between low- and high-altitude genotypes. In conclusion, we found clinal variation across an altitudinal gradient both in flowering time and the expression and regulation of genes in the flowering time control network, often independent of FLC, suggesting that the timing of flowering may contribute to altitudinal adaptation.Environmental gradients, such as temperature or water availability, provide an ideal setting to study how species adapt to contrasting environmental scenarios (Reich et al., 2003; Keller et al., 2013). Many studies have shown that phenotypic plant traits such as leaf number, allocation to reproductive biomass, and height change along environmental gradients (Etterson, 2004; Leger and Rice, 2007; Fischer et al., 2011), and some studies could correlate environmental clines to changes in allelic frequencies at specific candidate genes (Manel et al., 2010; Poncet et al., 2010; Fischer et al., 2013).Although allelic variation at genes with major effects may explain variation in some phenotypes, fine-tuning of other quantitative traits along an environmental gradient may require an adjustment of larger regulatory networks (Whitehead and Crawford, 2006; Hodgins-Davis and Townsend, 2009; Hodgins et al., 2013). In Arabidopsis (Arabidopsis thaliana), numerous genetic pathways have been studied extensively, mainly using laboratory accessions (Shinozaki and Yamaguchi-Shinozaki, 2007; Wellmer and Riechmann, 2010; Ó’Maoiléidigh et al., 2014). However, how consistently such pathways are expressed in natural populations, and how they respond to different environmental conditions, often remains unclear. Studying the expression of genetic pathways in natural genotypes originating from an environmental cline under a variety of climatic scenarios provides an ideal approach to understanding how plants can adapt to contrasting environments along a climatic gradient.Across altitudes, environmental gradients are particularly steep: climatic conditions, including temperature, solar radiation, and precipitation, may change dramatically on a small geographic scale (Körner, 2007), while daylength and other factors remain constant. Many phenotypic traits, such as height, total seed weight, leaf size, and allocation to vegetative reproduction, have been found to change along altitudinal gradients in plants (Byars et al., 2007; Gonzalo-Turpin and Hazard, 2009; Fischer et al., 2011). Among these, the timing of flowering (i.e. the transition from vegetative growth to the reproductive phase) is a key developmental phase transition in seasonal alpine environments, as its accuracy is crucial for reproductive success: too-early flowering increases the risk of encountering detrimental frost (Kollas et al., 2013), whereas time for seed maturation may run out if flowering starts too late (Inouye and Wielgolaski, 2003; Chuine, 2010). These contrasting selective pressures may change along an altitudinal gradient, where the vegetation period becomes shorter with increasing altitude.In Arabidopsis, an annual weed native to Eurasia and northern Africa, two different life cycles have been described (Koornneef et al., 2004; Alonso-Blanco et al., 2009): summer annuals germinate and flower within one growing season and do not require winter to initiate flowering; winter annuals germinate usually in autumn, overwinter as vegetative rosettes, and flower in the following spring. Accessions expressing a winter-annual life cycle need vernalization (a prolonged cold period) in order to initiate flowering; otherwise, they remain in a vegetative rosette stage for an extended period of time.On the molecular level, the transition to flowering is among the best-studied processes in plants (Wellmer and Riechmann, 2010; Andrés and Coupland, 2012), and in Arabidopsis, several genetic pathways controlling flowering are known. Signals from the vernalization pathway, photoperiod pathway, autonomous pathway, GA pathway, and plant age all contribute to ensuring the correct timing of flowering (Ehrenreich et al., 2009; Wellmer and Riechmann, 2010; Srikanth and Schmid, 2011). Within the vernalization pathway, a number of key players have been identified (Andrés and Coupland, 2012; Schmitz and Amasino, 2012; Song et al., 2012; Zografos and Sung, 2012). In winter annuals, a functional FRIGIDA (FRI) allele is required to activate FLOWERING LOCUS C (FLC). FLC strongly suppresses the flowering promoters FLOWERING LOCUS T (FT) and AGAMOUS LIKE20 (AGL20; also referred to as SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1) and thus inhibits flowering. During vernalization, VERNALIZATION INSENSITIVE3 (VIN3) represses FLC, and the repressed state is maintained in subsequent warm periods by epigenetic silencing (Crevillén and Dean, 2011; Zografos and Sung, 2012), allowing FT, AGL20, and, through positive feedback with AGL20, AGL24 (Liu et al., 2008) to initiate flowering. Many natural populations and most laboratory accessions, among them Columbia-0 (Col-0), carry nonfunctional FRI or FLC alleles and thus respond only weakly to vernalization, resulting in fast flowering, summer-annual life cycles (Johanson et al., 2000; Gazzani et al., 2003; Shindo et al., 2005).In addition to the well-studied FLC branch of the vernalization pathway, FLC-independent components of the vernalization response have been identified. For example, AGL19 has been found to promote flowering following vernalization without interacting with FLC (Schönrock et al., 2006), and relatives of FLC, the MADS AFFECTING FLOWERING genes (MAF1–MAF5; MAF1 is also referred to as FLOWERING LOCUS M [FLM]; De Bodt et al., 2003), have been shown to inhibit flowering in a similar way to FLC (Ratcliffe et al., 2003; Scortecci et al., 2003; Werner et al., 2005; Sung et al., 2006; Gu et al., 2013). Genes MAF2 to MAF5 (Ratcliffe et al., 2003) are arranged in a tandem gene array and vary extensively among natural populations (Caicedo et al., 2009; Rosloski et al., 2010), and several recent studies have associated this polymorphic region with natural variation in flowering time (Salomé et al., 2011; Silady et al., 2011; Lasky et al., 2012; Fournier-Level et al., 2013; Grillo et al., 2013), making these genes interesting candidates for studying associations between flowering time and ecological parameters.Associating genetic variation at a single gene with latitude or altitude has often proven to be difficult (Shindo et al., 2005; Stinchcombe et al., 2005; Méndez-Vigo et al., 2011), although Caicedo et al. (2004) found evidence for epistatic interactions between FRI and FLC alleles associated with latitude. Interestingly, some recent studies suggest that regulatory processes within the vernalization pathway may contribute to natural phenotypic variability (Shindo et al., 2006; Strange et al., 2011). Overall, the response to vernalization appears to be a complex process in natural populations, potentially involving epigenetic regulation of a number of genes. Therefore, to gain a better understanding of the involvement of this complex genetic network in the response to ecological parameters, it is essential to study multiple interacting genes of the vernalization pathway simultaneously.Here, we used 15 natural Arabidopsis genotypes originating from an altitudinal cline (800–2,700 m) in the Swiss Alps to study the associations between vernalization, flowering initiation, gene expression and regulation, and altitude. Importantly, all genotypes originated from a restricted geographic range; thus, confounding effects such as differences in daylength, as found along latitudinal clines, can be excluded. We measured flowering time and the expression of 12 genes of the vernalization pathway under different vernalization scenarios to assess whether the response to vernalization is associated with altitude. In particular, we tested the hypotheses that (1) flowering time correlates with altitude; (2) genotypes from high altitudes need longer vernalization periods to initiate flowering reliably; (3) gene expression and regulation of the vernalization pathway can explain flowering time; (4) gene expression and regulation of the vernalization pathway is associated with altitude; and (5) FLC-independent branches of the vernalization pathway are important for initiating flowering and, thus, for altitudinal adaptation in natural populations.     

拟南芥AtLH基因过量表达引起叶向下性卷曲和晚开花

AtLH基因是BcpLH基因在拟南芥(Arapsis thaliana L.)中的同源基因,含有两个编码双链RNA结合蛋白的结构域.在大白菜叶球发育过程中,BcpLH基因与包叶的卷曲有关.为研究AtLH的基因对叶卷曲这一重要生物学现象的调控作用,构建了35S:AtLH基因的正义表达载体并转化拟南芥.与野生型比较页言,转基因植株的花和叶中AtLH的表达量有显著增加,成为AtLH基因过量的植株.这些植株的莲座叶向外或向下卷曲,呈现明显的偏上性生长;而且抽苔和开花时间延迟;在营养生长期其短缩茎的叶腑处着生数个侧茎,表现为顶端优势减弱;在生殖生长期二级花序减少使得主花序更加发达,表现为顶端优势增强,转基因植株对激素的敏感性改变,IAA剌激根生长的作用增强,ABA抑制根生长的作用减弱.由此可见,AtLH基因的过量表达可引起转基因植株的叶片向下卷曲.     

拟南芥AtLH基因过量表达引起叶向下性卷曲和晚开花(英文)

AtLH基因是BcpLH基因在拟南芥(Arabidopsis thealiana L.)中的同源基因,含有两个编码双链RNA结合蛋白的结构域。在大白菜叶球发育过程中,BcpLH基因与包叶的卷曲有关。为研究AtLH基因对叶卷曲这一重要生物学现象的调控作用,构建了35S:AtLH基因的正义表达载体并转化拟南芥。与野生型比较而言,转基因植株的花和叶中AtLH的表达量有显著增加,成为AtLH基因过量表达的植株。这些植株的莲座叶向外或向下卷曲,呈现明显的偏上性生长;而且抽苔和开花时间延迟;在营养生长期其短缩茎的叶腋处着生数个侧茎,表现为顶端优势减弱;在生殖生长期二级花序减少使得主花序更加发达,表现为顶端优势增强;转基因植株对激素的敏感性改变,IAA刺激根生长的作用增强,ABA抑制根生长的作用减弱。由此可见,AtLH基因的过量表达可引起转基因植株的叶片向下卷曲。     

Flowering in darkness in Arabidopsis thaliana

A modified method for studying the initiation of flowering in darkness (dark flowering, DF) in Arabidopsis thaliana has been developed, and the DF process has been examined with the aid of late-flowering mutants. A majority of plants developed floral buds by the use of liquid-shaken cultures in darkness. The late-flowering phenotype in gi and co mutants and early-flowering phenotype in a hy2 mutant disappeared in DF. It was found that wild-type plants grown under DF conditions express light-regulated genes and develop appropriate leaf architecture, as do the light-grown plants, without the apparent differentiation of chloroplasts. The shift experiments from darkness to light revealed the critical duration of growth in darkness for the initiation of DF. These results indicate that the DF process to the initiation of flowering is a mode of development distinct from that in light in Arabidopsis .     

The Conserved PFT1 Tandem Repeat Is Crucial for Proper Flowering in Arabidopsis thaliana

It is widely appreciated that short tandem repeat (STR) variation underlies substantial phenotypic variation in organisms. Some propose that the high mutation rates of STRs in functional genomic regions facilitate evolutionary adaptation. Despite their high mutation rate, some STRs show little to no variation in populations. One such STR occurs in the Arabidopsis thaliana gene PFT1 (MED25), where it encodes an interrupted polyglutamine tract. Although the PFT1 STR is large (∼270 bp), and thus expected to be extremely variable, it shows only minuscule variation across A. thaliana strains. We hypothesized that the PFT1 STR is under selective constraint, due to previously undescribed roles in PFT1 function. We investigated this hypothesis using plants expressing transgenic PFT1 constructs with either an endogenous STR or synthetic STRs of varying length. Transgenic plants carrying the endogenous PFT1 STR generally performed best in complementing a pft1 null mutant across adult PFT1-dependent traits. In stark contrast, transgenic plants carrying a PFT1 transgene lacking the STR phenocopied a pft1 loss-of-function mutant for flowering time phenotypes and were generally hypomorphic for other traits, establishing the functional importance of this domain. Transgenic plants carrying various synthetic constructs occupied the phenotypic space between wild-type and pft1 loss-of-function mutants. By varying PFT1 STR length, we discovered that PFT1 can act as either an activator or repressor of flowering in a photoperiod-dependent manner. We conclude that the PFT1 STR is constrained to its approximate wild-type length by its various functional requirements. Our study implies that there is strong selection on STRs not only to generate allelic diversity, but also to maintain certain lengths pursuant to optimal molecular function.     

Quantitative Variation in Responses to Root Spatial Constraint within Arabidopsis thaliana

Among the myriad of environmental stimuli that plants utilize to regulate growth and development to optimize fitness are signals obtained from various sources in the rhizosphere that give an indication of the nutrient status and volume of media available. These signals include chemical signals from other plants, nutrient signals, and thigmotropic interactions that reveal the presence of obstacles to growth. Little is known about the genetics underlying the response of plants to physical constraints present within the rhizosphere. In this study, we show that there is natural variation among Arabidopsis thaliana accessions in their growth response to physical rhizosphere constraints and competition. We mapped growth quantitative trait loci that regulate a positive response of foliar growth to short physical constraints surrounding the root. This is a highly polygenic trait and, using quantitative validation studies, we showed that natural variation in EARLY FLOWERING3 (ELF3) controls the link between root constraint and altered shoot growth. This provides an entry point to study how root and shoot growth are integrated to respond to environmental stimuli.     

Genetic Architecture of Natural Variation of Telomere Length in Arabidopsis thaliana

Telomeres represent the repetitive sequences that cap chromosome ends and are essential for their protection. Telomere length is known to be highly heritable and is derived from a homeostatic balance between telomeric lengthening and shortening activities. Specific loci that form the genetic framework underlying telomere length homeostasis, however, are not well understood. To investigate the extent of natural variation of telomere length in Arabidopsis thaliana, we examined 229 worldwide accessions by terminal restriction fragment analysis. The results showed a wide range of telomere lengths that are specific to individual accessions. To identify loci that are responsible for this variation, we adopted a quantitative trait loci (QTL) mapping approach with multiple recombinant inbred line (RIL) populations. A doubled haploid RIL population was first produced using centromere-mediated genome elimination between accessions with long (Pro-0) and intermediate (Col-0) telomere lengths. Composite interval mapping analysis of this population along with two established RIL populations (Ler-2/Cvi-0 and Est-1/Col-0) revealed a number of shared and unique QTL. QTL detected in the Ler-2/Cvi-0 population were examined using near isogenic lines that confirmed causative regions on chromosomes 1 and 2. In conclusion, this work describes the extent of natural variation of telomere length in A. thaliana, identifies a network of QTL that influence telomere length homeostasis, examines telomere length dynamics in plants with hybrid backgrounds, and shows the effects of two identified regions on telomere length regulation.     

Ecotype-Specific Expression of a Flowering Mutant Phenotype in Arabidopsis thaliana

The majority of mutations that delay flowering in Arabidopsis thaliana have been identified in studies of the Landsberg erecta (Ler) ecotype. In this report we describe a gene (referred to as FLD) that, when mutated, delays flowering in the Columbia ecotype but has a minimal phenotype in the Ler genetic background. The late-flowering phenotype of fld mutants requires a non-Ler allele of another gene involved in the control of flowering time, Flowering Locus C. fld mutants retain a photoperiod response, and the flowering time of fld mutants can be reduced by cold treatment and low red/far-red light ratios.     

Germination and Flowering in Arabidopsis thaliana in Sterile Culture

The optimal conditions for the germination, growth, and flowering of an Indian strain of Arabidopsis thaliana were investigated in sterile culture. Seeds require a cold treatment to germinate, and the most effective temperature is 8?C for 48 hours. Germination after vernalization is promoted by red light and inhibited by far-red. Unvernalized seeds germinated after 31 days and flower buds appeared in 61 days. On verbalization and subsequent transfer to a temperature of 25?C and a light intensity of 4300 lux of fluorescent light, plants flowered in 25 days. Under 7000 lux of light rich in both blue and red region of the spectum, plants flowered in only 12 days. A minimum of five long-day photocyeles appeared to be necessary for flowering. Kinetin (10^?7M) and gibberellic acid (10^?7M, 10^?6M) accelerated flower formation. Kinetin and 2,4-D also catised specific types of callussing from different regions of the plant.     

Responses of Arabidopsis thaliana to challenge by Pseudomonas syringae

Plants are continually exposed to a variety of potentially pathogenic microbes, and the interactions between plants and pathogenic invaders determine the outcome, disease or disease resistance. To defend themselves, plants have developed a sophisticated immune system. Unlike animals, however, they do not have specialized immune cells and, thus all plant cells appear to have the innate ability to recognize pathogens and turn on an appropriate defense response. Using genetic, genomic and biochemical methods, tremendous advances have been made in understanding how plants recognize pathogens and mount effective defenses. The primary immune response is induced by microbe-associated molecular patterns (MAMPs). MAMP receptors recognize the presence of probable pathogens and evoke defense. In the co-evolution of plant-microbe interactions, pathogens gained the ability to make and deliver effector proteins to suppress MAMP-induced defense responses. In response to effector proteins, plants acquired R-proteins to directly or indirectly monitor the presence of effector proteins and activate an effective defense response. In this review we will describe and discuss the plant immune responses induced by two types of elicitors, PAMPs and effector proteins.