Transition In Arabidopsis Research Articles

Identification and characterization of FaSOC1, a homolog of SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 from strawberry

A MADS-box gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) integrates multiple flowering signals to regulate floral transition in Arabidopsis. Strawberry (Fragaria spp.) is an economically important fruit crop, but its molecular control of flowering is largely unknown. In this study, a SOC1-like gene, FaSOC1, was isolated and characterized from strawberry. The open reading frame of FaSOC1 was 648bp, encoding a protein of 215 amino acids. Sequence alignment and phylogenetic analysis showed that the FaSOC1 protein contained a highly conserved MADS domain and a SOC1 motif, and that it was a member of the SOC1-like genes of dicots. The FaSOC1 protein mainly localized in the cytoplasm of onion epidermal cells and Arabidopsis protoplasts, and showed no transcriptional activation activity in yeast cells. Under the floral induction conditions, the expression of FaSOC1 increased during the first 2weeks of short-day treatment, but declined dramatically during three to 4weeks. FaSOC1 was highly expressed in reproductive organs, including shoot apices, floral buds, flowers, stamens and sepals. Overexpression of FaSOC1 in wild-type Arabidopsis caused early flowering and upregulated the expression of flowering time genes LFY and AP1. In addition, the yeast two-hybrid and BiFC assays confirmed that FaSOC1 could interact with AGL24. In conclusion, these results suggest that FaSOC1 is a flowering promoter in strawberry.

Starch metabolism and antiflorigenic signals modulate the juvenile‐to‐adult phase transition in Arabidopsis

Knowledge of how environment influences juvenility could help with crop scheduling in commercial horticulture, decrease time to flowering and reduce waste with resulting benefits for the environment through lower inputs and energy required per unit of marketable product.In the manuscript, using an experimental assay that allows the length of the juvenile phase to be estimated in response to floral competence, and several mutants impaired in different genetic pathways, we show that multiple inputs influence the timing of the juvenile‐to‐adult phase transition in Arabidopsis.

Heterochromatin dynamics during developmental transitions in Arabidopsis — a focus on ribosomal DNA loci

The Arabidopsis chromosomes contain conspicuous heterochromatin domains comprising the repetitive 45S and 5S ribosomal DNA loci as well as centromeric and pericentromeric repeats that organize into chromocenters during interphase. During developmental phase transitions such as seed maturation, germination, seedling growth and flowering that require large-scale reprogramming of gene expression patterns, the organization of repetitive sequences into chromocenters dynamically changes. Here we illustrate recent studies that shed light on the heterochromatin dynamics in cotyledons, the first aerial tissues preformed in the embryo, and in true leaves. We will summarize available data for the 5S rDNA repeat loci, in particular their chromatin organization and expression dynamics during the first days of post-germination development, and discuss how the plant accommodates 5S rRNA transcription during large-scale chromatin reorganization events.

The inhibitory effect of ABA on floral transition is mediated by ABI5 in Arabidopsis

Seed germination and flowering initiation are both transitions responding to similar seasonal cues. This study shows that ABSCISIC ACID-INSENSITIVE MUTANT 5 (ABI5), a bZIP transcription factor, which plays an important role in the abscisic acid (ABA)-arrested seed germination, is robustly associated with the floral transition in Arabidopsis. Under long-day conditions, overexpression of ABI5 could delay floral transition through upregulating FLOWERING LOCUS C (FLC) expression. In contrast, ectopically overexpressing FLC in an abi5 mutant reversed the earlier flowering phenotype. Further analysis indicated that transactivation of FLC could be promoted by ABI5 and/or other abscisic acid-responsive element (ABRE)-binding factors (ABFs). The expression of FLC that was promoted by ABI5 and/or other ABFs could be blocked in a triple SNF1-related protein kinase (SnRK) mutant, snrk2.2/2.3/2.6, despite the presence of ABA. In sharp contrast, when SnRK2.6 was coexpressed, the reduction of transactivity of FLC was reverted in mesophyll protoplasts of snrk2.2/2.3/2.6. Additional results from analysing transgenic plants carrying mutations of phosphoamino acids (ABI5 S42AS145AT201A), which are conserved in ABI5, suggested that SnRK2-mediated ABI5 and/or ABF phosphorylation may be crucial for promoting FLC expression. The transgenic plants ABI5 S42AS145AT201A were insensitive to ABA in seed germination, in addition to having an earlier flowering phenotype. Direct binding of ABI5 to the ABRE/G-box promoter elements existing in FLC was demonstrated by chromatin immunoprecipitation. Mutations at the ABRE/G-box regions in FLC promoter sequences abolished the ABI5-promoted transactivation of FLC. In summary, these results may decipher the inhibitory effect of ABA on floral transition in Arabidopsis.

An acyl-CoA-binding protein from grape that is induced through ER stress confers morphological changes and disease resistance in Arabidopsis

We here report characterization of a grape (Vitis vinifera) acyl-CoA-binding protein (VvACBP). Expression of VvACBP was detected in grape leaves exposed to tunicamycin-induced endoplasmic reticulum (ER) stress as well as cold and heat shock treatments. In tendrils and peduncles, however, high-temperature treatment induced BiP (luminal binding protein) expression, a marker of ER stress in berry skin, but not VvACBP expression. We hypothesize that VvACBP may be sorted to the periphery of plant cells. Transgenic Arabidopsis plants, expressing VvACBP, exhibited slowed-down floral transition. The gene expression of proteins related to the photoperiodic pathway, CONSTANS, FLOWERING LOCUS T (FT), and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), was down-regulated in transgenic seedlings. These results underscore the possibility that VvACBP may affect the regulation of floral transition in Arabidopsis by suppressing the photoperiodic pathway. The transgenic Arabidopsis plants also exhibited morphological changes such as thicker inflorescences and rosette leaves. In addition, the rosette leaves of the transgenic plants had higher anthocyanin, total phenol, and chlorophyll contents than those of the control plants. Finally, the transgenic plants showed disease resistance to Pseudomonas syringae and Colletotrichum higginsianum, suggesting that VvACBP may also enhance disease resistance in grapevine.

OSD1 Promotes Meiotic Progression via APC/C Inhibition and Forms a Regulatory Network with TDM and CYCA1;2/TAM

Cell cycle control is modified at meiosis compared to mitosis, because two divisions follow a single DNA replication event. Cyclin-dependent kinases (CDKs) promote progression through both meiosis and mitosis, and a central regulator of their activity is the APC/C (Anaphase Promoting Complex/Cyclosome) that is especially required for exit from mitosis. We have shown previously that OSD1 is involved in entry into both meiosis I and meiosis II in Arabidopsis thaliana; however, the molecular mechanism by which OSD1 controls these transitions has remained unclear. Here we show that OSD1 promotes meiotic progression through APC/C inhibition. Next, we explored the functional relationships between OSD1 and the genes known to control meiotic cell cycle transitions in Arabidopsis. Like osd1, cyca1;2/tam mutation leads to a premature exit from meiosis after the first division, while tdm mutants perform an aberrant third meiotic division after normal meiosis I and II. Remarkably, while tdm is epistatic to tam, osd1 is epistatic to tdm. We further show that the expression of a non-destructible CYCA1;2/TAM provokes, like tdm, the entry into a third meiotic division. Finally, we show that CYCA1;2/TAM forms an active complex with CDKA;1 that can phosphorylate OSD1 in vitro. We thus propose that a functional network composed of OSD1, CYCA1;2/TAM, and TDM controls three key steps of meiotic progression, in which OSD1 is a meiotic APC/C inhibitor.

Functional characterization of FT and MFT ortholog genes in orchid (Dendrobium nobile Lindl) that regulate the vegetative to reproductive transition in Arabidopsis

Genes belonging to the phosphoethanolamine binding protein (PEBP) superfamily play important roles in controlling the switch between vegetative and reproductive growth in higher plants. Here we reported the isolation of two genes from the PEBP superfamily in Dendrobium nobile Lindl homologous to FLOWERING LOCUS T (FT) and MOTHER OF FT (MFT). These two genes, designated as DnFT and DnMFT, were predominantly expressed in the auxiliary buds and leaves of the plant. In auxiliary buds, DnFT was expressed at a higher level in young buds than in mature buds, while mature leaves expressed more DnFT than young ones. Low temperature treatment led to an increased expression of DnFT in leaves, but a decreased expression in buds. In contrast, the expression of DnMFT increased in buds and decreased in leaves during flower bud development and was not influenced by low temperature treatment. Ectopic expression of DnFT in Arabidopsis plants showed an early-flowering phenotype and inflorescence indeterminacy loss. Over-expression of DnMFT in Arabidopsis led to slightly late-flowering. Our results revealed that DnFT functions as a floral inducer in D. nobile Lindl by regulating flower transition in a similar way to its ortholog in Arabidopsis. Early flowering, induced by a low temperature treatment, was probably due to the activation of DnFT transcription in D. nobile Lindl.

A Companion Cell–Dominant and Developmentally Regulated H3K4 Demethylase Controls Flowering Time in Arabidopsis via the Repression of FLC Expression

Flowering time relies on the integration of intrinsic developmental cues and environmental signals. FLC and its downstream target FT are key players in the floral transition in Arabidopsis. Here, we characterized the expression pattern and function of JMJ18, a novel JmjC domain-containing histone H3K4 demethylase gene in Arabidopsis. JMJ18 was dominantly expressed in companion cells; its temporal expression pattern was negatively and positively correlated with that of FLC and FT, respectively, during vegetative development. Mutations in JMJ18 resulted in a weak late-flowering phenotype, while JMJ18 overexpressors exhibited an obvious early-flowering phenotype. JMJ18 displayed demethylase activity toward H3K4me3 and H3K4me2, and bound FLC chromatin directly. The levels of H3K4me3 and H3K4me2 in chromatins of FLC clade genes and the expression of FLC clade genes were reduced, whereas FT expression was induced and the protein expression of FT increased in JMJ18 overexpressor lines. The early-flowering phenotype caused by the overexpression of JMJ18 was mainly dependent on the functional FT. Our findings suggest that the companion cell–dominant and developmentally regulated JMJ18 binds directly to the FLC locus, reducing the level of H3K4 methylation in FLC chromatin and repressing the expression of FLC, thereby promoting the expression of FT in companion cells to stimulate flowering.

Whole‐genome expression patterns in LTP knockdown Arabidopsis plants

AbstractOur lab studies the aging process in plants, using the plant model Arabidopsis thaliana. Arabidopsis’ small size and rapid life cycle make it an attractive model to study plant senescence. Previous research in our laboratory suggests that as Arabidopsis undergoes the developmental transition from vegetative growth to flowering, ascorbate peroxidase (APX) activity that is responsible for scavenging H2 O2 is repressed and 13‐lipoxygenase (LOX) is activated. LOX catalyzes the first reaction in oxylipin‐signaling pathways, which generate a multitude of lipid signaling molecules. We specifically focus on the possibility that lipid transfer proteins may carry signals during the aging process of the plant. Lipid transfer proteins are small, basic proteins present in the plant cell wall. Other data from our lab showed an up‐regulation of two lipid transfer proteins as the plant transitions from the vegetative to flowering stage. These data suggest that oxylipins may be involved as a signal between meristems and leaves during the vegetative to flowering transition in Arabidopsis. The purpose of this study is to compare gene expression patterns of Arabidopsis in wild type and LTP RNAi knockdown mutants, in meristems and flowers during different developmental stages and determine how gene expression patterns are altered in RNAi knockdowns. Our current RNAi knockdown mutants in Arabidopsis show uncontrolled growth producing an abundant number of flowers and seeds and live six times longer than an average wild type plant. Based on our knockdown phenotypes, we predict that downregulation of these genes may play a major role in the inhibition of meristem arrest.

Genome‐wide identification of SOC1 and SVP targets during the floral transition in Arabidopsis

Floral transition in Arabidopsis is tightly controlled by complex genetic regulatory networks in response to endogenous and environmental flowering signals. SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and SHORT VEGETATIVE PHASE (SVP), two key MADS-domain transcription factors, perceive these signals and function as antagonistic flowering regulators. To understand how these factors mediate floral transition, we mapped in vivo binding sites of SOC1 and SVP using chromatin immunoprecipitation followed by hybridization to whole-genome tiling arrays (ChIP-chip). Genes that encoded proteins with transcription regulator activity and transcription factor activity were the most enriched groups of genes of those bound by SOC1 and SVP, which indicates their central roles in flowering regulatory networks. In combination with gene expression microarray studies, we further identified the genes whose expression was controlled directly by SOC1 or SVP. Among the common direct targets identified, APETALA2 (AP2)-like genes that repress FT and SOC1 expression were down-regulated by SOC1, but up-regulated by SVP, revealing a complex feedback regulation among the key genes that determine the integration of flowering signals. SOC1 regulatory regions were also accessed by SOC1 itself and SVP, suggesting that self-activation and repression by SVP contribute to the control of SOC1 expression. In addition, ChIP-chip analysis demonstrated that miR156e and miR172a, which are involved in the regulation of AP2-like genes, were direct targets of SOC1 and SVP, respectively. Taken together, these findings revealed that feedback regulatory loops mediated by SOC1 and SVP are essential components of the gene regulatory networks that underpin the integration of flowering signals during floral transition.

AKIN10 and FUSCA3 interact to control lateral organ development and phase transitions in Arabidopsis

The Snf1 (sucrose non-fermenting-1)/AMPK (AMP-activated protein kinase)/SnRK1 (Snf1-related protein kinase 1) kinases act as sensors of energy status in eukaryotes. Despite the important role of these kinases in regulation of cellular responses to metabolic stress, only a few SnRK1 substrates have been identified. Using yeast two-hybrid screens, we isolated AKIN10 as an interactor of the B3-domain transcription factor FUSCA3 (FUS3), an essential regulator of seed maturation in Arabidopsis. Pull-down and bi-molecular fluorescence complementation (BiFC) assays confirm the interaction in vitro and in planta, respectively. In-gel kinase assays show that AKIN10 phosphorylates FUS3 and that the N-terminal domain of FUS3 is required for AKIN10 phosphorylation. Mutations of three serines (fus3(S55A/S56A/S57A) ) within a partial SnRK1 consensus sequence in the N-terminal region of FUS3 reduce greatly FUS3 phosphorylation by AKIN10, which indicates that these serines are the predominant AKIN10 target sites. In a cell-free system, AKIN10 positively regulates FUS3 stability, as overexpression of AKIN10 delayed the degradation of the recombinant FUS3. Plants over-expressing AKIN10 show delayed seed germination, vegetative growth and flowering time, indicating that AKIN10 antagonizes the embryonic-to-vegetative and vegetative-to-reproductive phase transitions. Furthermore, overexpression of AKIN10 alters cotyledon, silique and floral organ development, suggesting that AKIN10 regulates lateral organ development. Genetic interaction studies show that the fus3-3 mutation partially rescues the phase transition and organ development defects caused by AKIN10 overexpression. Taken together, these findings indicate that FUS3 and AKIN10 interact physically and share overlapping pathways to regulate developmental phase transitions and organogenesis in Arabidopsis.

Molecular Foundations of Reproductive Lethality in Arabidopsis thaliana

The SeedGenes database (www.seedgenes.org) contains information on more than 400 genes required for embryo development in Arabidopsis. Many of these EMBRYO-DEFECTIVE (EMB) genes encode proteins with an essential function required throughout the life cycle. This raises a fundamental question. Why does elimination of an essential gene in Arabidopsis often result in embryo lethality rather than gametophyte lethality? In other words, how do mutant (emb) gametophytes survive and participate in fertilization when an essential cellular function is disrupted? Furthermore, why do some mutant embryos proceed further in development than others? To address these questions, we first established a curated dataset of genes required for gametophyte development in Arabidopsis based on information extracted from the literature. This provided a basis for comparison with EMB genes obtained from the SeedGenes dataset. We also identified genes that exhibited both embryo and gametophyte defects when disrupted by a loss-of-function mutation. We then evaluated the relationship between mutant phenotype, gene redundancy, mutant allele strength, gene expression pattern, protein function, and intracellular protein localization to determine what factors influence the phenotypes of lethal mutants in Arabidopsis. After removing cases where continued development potentially resulted from gene redundancy or residual function of a weak mutant allele, we identified numerous examples of viable mutant (emb) gametophytes that required further explanation. We propose that the presence of gene products derived from transcription in diploid (heterozygous) sporocytes often enables mutant gametophytes to survive the loss of an essential gene in Arabidopsis. Whether gene disruption results in embryo or gametophyte lethality therefore depends in part on the ability of residual, parental gene products to support gametophyte development. We also highlight here 70 preglobular embryo mutants with a zygotic pattern of inheritance, which provide valuable insights into the maternal-to-zygotic transition in Arabidopsis and the timing of paternal gene activation during embryo development.

Brahma Is Required for Proper Expression of the Floral Repressor FLC in Arabidopsis

BackgroundBRAHMA (BRM) is a member of a family of ATPases of the SWI/SNF chromatin remodeling complexes from Arabidopsis. BRM has been previously shown to be crucial for vegetative and reproductive development.Methodology/Principal FindingsHere we carry out a detailed analysis of the flowering phenotype of brm mutant plants which reveals that, in addition to repressing the flowering promoting genes CONSTANS (CO), FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1), BRM also represses expression of the general flowering repressor FLOWERING LOCUS C (FLC). Thus, in brm mutant plants FLC expression is elevated, and FLC chromatin exhibits increased levels of histone H3 lysine 4 tri-methylation and decreased levels of H3 lysine 27 tri-methylation, indicating that BRM imposes a repressive chromatin configuration at the FLC locus. However, brm mutants display a normal vernalization response, indicating that BRM is not involved in vernalization-mediated FLC repression. Analysis of double mutants suggests that BRM is partially redundant with the autonomous pathway. Analysis of genetic interactions between BRM and the histone H2A.Z deposition machinery demonstrates that brm mutations overcome a requirement of H2A.Z for FLC activation suggesting that in the absence of BRM, a constitutively open chromatin conformation renders H2A.Z dispensable.Conclusions/SignificanceBRM is critical for phase transition in Arabidopsis. Thus, BRM represses expression of the flowering promoting genes CO, FT and SOC1 and of the flowering repressor FLC. Our results indicate that BRM controls expression of FLC by creating a repressive chromatin configuration of the locus.

The cyclin-A CYCA1;2/TAM is required for the meiosis I to meiosis II transition and cooperates with OSD1 for the prophase to first meiotic division transition.

Meiosis halves the chromosome number because its two divisions follow a single round of DNA replication. This process involves two cell transitions, the transition from prophase to the first meiotic division (meiosis I) and the unique meiosis I to meiosis II transition. We show here that the A-type cyclin CYCA1;2/TAM plays a major role in both transitions in Arabidopsis. A series of tam mutants failed to enter meiosis II and thus produced diploid spores and functional diploid gametes. These diploid gametes had a recombined genotype produced through the single meiosis I division. In addition, by combining the tam-2 mutation with AtSpo11-1 and Atrec8, we obtained plants producing diploid gametes through a mitotic-like division that were genetically identical to their parents. Thus tam alleles displayed phenotypes very similar to that of the previously described osd1 mutant. Combining tam and osd1 mutations leads to a failure in the prophase to meiosis I transition during male meiosis and to the production of tetraploid spores and gametes. This suggests that TAM and OSD1 are involved in the control of both meiotic transitions.

Identifying the Functional Orthologs of Lipid Transfer Proteins (LTPs) for Developmental Regulation in Flowering Plants

During the floral transition in Arabidopsis, 13‐HOO‐FA, a possible lipid hydroperoxide precursor for signaling molecules, increases in leaves due to lipoxygenase activity. Results have shown the up‐regulation of two lipid transfer protein (LTP) genes, AtLTPf1 and AtLTPf2, at the floral transition. LTPs may act as signal carriers that transfer lipids, like oxylipins, between cells for developmental events. The purpose of this experiment is to locate orthologs of AtLTPf1 and AtLTPf2 from Arabidopsis (a dicot) in rice (a monocot) using bioinformatics coupled with expression pattern analyses. Our phylogenetic trees show LTP homologs, and we hypothesize that the most closely related genes, OsLTPf1 and OsLTPf2 from rice, mirror AtLTPf1 and AtLTPf2 expression, respectively. Through a comparison of various tissues at different stages of development in both plant species, our data suggests that AtLTPf1 and OsLTPf1 are orthologs. Further analysis of these LTPs may clarify their function and elucidate the signaling pathways involved in floral transition and developmental regulation. These LTPs may provide targets for genetic modification to alter plant development. Supported by NIH‐SCORE GM08101

The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis.

The ability of plants to adapt to changing light conditions depends on a protein kinase network in the chloroplast that leads to the reversible phosphorylation of key proteins in the photosynthetic membrane. Phosphorylation regulates, in a process called state transition, a profound reorganization of the electron transfer chain and remodeling of the thylakoid membranes. Phosphorylation governs the association of the mobile part of the light-harvesting antenna LHCII with either photosystem I or photosystem II. Recent work has identified the redox-regulated protein kinase STN7 as a major actor in state transitions, but the nature of the corresponding phosphatases remained unknown. Here we identify a phosphatase of Arabidopsis thaliana, called PPH1, which is specifically required for the dephosphorylation of light-harvesting complex II (LHCII). We show that this single phosphatase is largely responsible for the dephosphorylation of Lhcb1 and Lhcb2 but not of the photosystem II core proteins. PPH1, which belongs to the family of monomeric PP2C type phosphatases, is a chloroplast protein and is mainly associated with the stroma lamellae of the thylakoid membranes. We demonstrate that loss of PPH1 leads to an increase in the antenna size of photosystem I and to a strong impairment of state transitions. Thus phosphorylation and dephosphorylation of LHCII appear to be specifically mediated by the kinase/phosphatase pair STN7 and PPH1. These two proteins emerge as key players in the adaptation of the photosynthetic apparatus to changes in light quality and quantity.

A plant-specific histone H3 lysine 4 demethylase represses the floral transition in Arabidopsis

Histone demethylation regulates chromatin structure and gene expression, and is catalyzed by various histone demethylases. Trimethylation of histone H3 at lysine 4 (H3K4) is coupled to active gene expression; trimethyl H3K4 is demethylated by Jumonj C (JmjC) domain-containing demethylases in mammals. Here we report that a plant-specific JmjC domain-containing protein known as PKDM7B (At4g20400) demethylates trimethyl H3K4. PKDM7B mediates H3K4 demethylation in a key floral promoter, FLOWERING LOCUS T (FT), and an FT homolog, TWIN SISTER OF FT (TSF), and represses their expression to inhibit the floral transition in Arabidopsis. Our findings suggest that there are at least two distinct sub-families of JmjC domain-containing demethylases that demethylate the active trimethyl H3K4 mark in eukaryotic genes, and reveal a plant-specific JmjC domain enzyme capable of H3K4 demethylation.

Integrating hormones into the floral‐transition pathway of Arabidopsis thaliana

The transition from vegetative to reproductive growth is a major phase change in angiosperms. In annual plants such as Arabidopsis thaliana (Arabidopsis), this change is irreversible, and as such, the regulation of its timing must be tightly controlled. Plant hormone (phytohormone) signalling is known to regulate suites of morphogenic processes in Arabidopsis a role in flowering-time control is starting to emerge as one key-controlling step. This review focuses on experimental evidence in the Arabidopsis that both classical and newly described phytohormones serve within the signal network leading to a reproductive phase transition, as both positive and repressive elements, depending on the phytohormone and growth conditions. Examples of genetic and pharmacological experiments that implicate phytohormones as components of the floral-timing syndrome will be described. I hope that this review will serve as a primer for future research on the mechanisms of action for each respective phytohormone on the floral transition in Arabidopsis, and lead to further experimentation on the crosstalk that likely bridges between them.

The Sequential Action of miR156 and miR172 Regulates Developmental Timing in Arabidopsis

The transition from the juvenile to the adult phase of shoot development in plants is accompanied by changes in vegetative morphology and an increase in reproductive potential. Here, we describe the regulatory mechanism of this transition. We show that miR156 is necessary and sufficient for the expression of the juvenile phase, and regulates the timing of the juvenile-to-adult transition by coordinating the expression of several pathways that control different aspects of this process. miR156 acts by repressing the expression of functionally distinct SPL transcription factors. miR172 acts downstream of miR156 to promote adult epidermal identity. miR156 regulates the expression of miR172 via SPL9 which, redundantly with SPL10, directly promotes the transcription of miR172b. Thus, like the larval-to-adult transition in Caenorhabditis elegans, the juvenile-to-adult transition in Arabidopsis is mediated by sequentially operating miRNAs. miR156 and miR172 are positively regulated by the transcription factors they target, suggesting that negative feedback loops contribute to the stability of the juvenile and adult phases.

Cold- and light-induced changes in the transcriptome of wheat leading to phase transition from vegetative to reproductive growth.

BackgroundFor plants to flower at the appropriate time, they must be able to perceive and respond to various internal and external cues. Wheat is generally a long-day plant that will go through phase transition from vegetative to floral growth as days are lengthening in spring and early summer. In addition to this response to day-length, wheat cultivars may be classified as either winter or spring varieties depending on whether they require to be exposed to an extended period of cold in order to become competent to flower. Using a growth regime to mimic the conditions that occur during a typical winter in Britain, and a microarray approach to determine changes in gene expression over time, we have surveyed the genes of the major pathways involved in floral transition. We have paid particular attention to wheat orthologues and functional equivalents of genes involved in the phase transition in Arabidopsis. We also surveyed all the MADS-box genes that could be identified as such on the Affymetrix genechip wheat genome array.ResultsWe observed novel responses of several genes thought to be of major importance in vernalisation-induced phase transition, and identified several MADS-box genes that might play an important role in the onset of flowering. In addition, we saw responses in genes of the Gibberellin pathway that would indicate that this pathway also has some role to play in phase transition.ConclusionPhase transition in wheat is more complex than previously reported, and there is evidence that day-length has an influence on genes that were once thought to respond exclusively to an extended period of cold.