RESUMEN
Optimal plant growth performance requires that the presence and action of growth signals, such as gibberellins (GAs), are coordinated with the availability of photo-assimilates. Here, we studied the links between GA biosynthesis and carbon availability, and the subsequent effects on growth. We established that carbon availability, light and dark cues, and the circadian clock ensure the timing and magnitude of GA biosynthesis and that disruption of these factors results in reduced GA levels and expression of downstream genes. Carbon-dependent nighttime induction of gibberellin 3-beta-dioxygenase 1 (GA3ox1) was severely hampered when preceded by reduced daytime light availability, leading specifically to reduced bioactive GA4 levels, and coinciding with a decline in leaf expansion rate during the night. We attributed this decline in leaf expansion mostly to reduced photo-assimilates. However, plants in which GA limitation was alleviated had significantly improved leaf expansion, demonstrating the relevance of GAs in growth control under varying carbon availability. Carbon-dependent expression of upstream GA biosynthesis genes (Kaurene synthase and gibberellin 20 oxidase 1, GA20ox1) was not translated into metabolite changes within this short timeframe. We propose a model in which the extent of nighttime biosynthesis of bioactive GA4 by GA3ox1 is determined by nighttime consumption of starch reserves, thus providing day-to-day adjustments of GA responses.
Asunto(s)
Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Carbono/metabolismo , Relojes Circadianos/fisiología , Giberelinas/metabolismo , Fotosíntesis/fisiología , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo , Adaptación Ocular/fisiología , Adaptación a la Oscuridad/fisiología , Variación Genética , Genotipo , Desarrollo de la Planta/efectos de los fármacosRESUMEN
Drought at flowering and grain filling greatly reduces maize (Zea mays) yield. Climate change is causing earlier and longer-lasting periods of drought, which affect the growth of multiple maize organs throughout development. To study how long periods of water deficit impact the dynamic nature of growth, and to determine how these relate to reproductive drought, we employed a high-throughput phenotyping platform featuring precise irrigation, imaging systems, and image-based biomass estimations. Prolonged drought resulted in a reduction of growth rate of individual organs-though an extension of growth duration partially compensated for this-culminating in lower biomass and delayed flowering. However, long periods of drought did not affect the highly organized succession of maximal growth rates of the distinct organs, i.e. leaves, stems, and ears. Two drought treatments negatively affected distinct seed yield components: Prolonged drought mainly reduced the number of spikelets, and drought during the reproductive period increased the anthesis-silking interval. The identification of these divergent biomass and yield components, which were affected by the shift in duration and intensity of drought, will facilitate trait-specific breeding toward future climate-resilient crops.
Asunto(s)
Estrés Fisiológico , Zea mays/fisiología , Biomasa , Cambio Climático , Sequías , Flores/crecimiento & desarrollo , Flores/fisiología , Fitomejoramiento , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/fisiología , Tallos de la Planta/crecimiento & desarrollo , Tallos de la Planta/fisiología , Agua/fisiología , Zea mays/crecimiento & desarrolloRESUMEN
HISTONE MONOUBIQUITINATION1 (HUB1) and its paralog HUB2 act in a conserved heterotetrameric complex in the chromatin-mediated transcriptional modulation of developmental programs, such as flowering time, dormancy, and the circadian clock. The KHD1 and SPEN3 proteins were identified as interactors of the HUB1 and HUB2 proteins with in vitro RNA-binding activity. Mutants in SPEN3 and KHD1 had reduced rosette and leaf areas. Strikingly, in spen3 mutants, the flowering time was slightly, but significantly, delayed, as opposed to the early flowering time in the hub1-4 mutant. The mutant phenotypes in biomass and flowering time suggested a deregulation of their respective regulatory genes CIRCADIAN CLOCK-ASSOCIATED1 (CCA1) and FLOWERING LOCUS C (FLC) that are known targets of the HUB1-mediated histone H2B monoubiquitination (H2Bub). Indeed, in the spen3-1 and hub1-4 mutants, the circadian clock period was shortened as observed by luciferase reporter assays, the levels of the CCA1α and CCA1ß splice forms were altered, and the CCA1 expression and H2Bub levels were reduced. In the spen3-1 mutant, the delay in flowering time was correlated with an enhanced FLC expression, possibly due to an increased distal versus proximal ratio of its antisense COOLAIR transcript. Together with transcriptomic and double-mutant analyses, our data revealed that the HUB1 interaction with SPEN3 links H2Bub during transcript elongation with pre-mRNA processing at CCA1 Furthermore, the presence of an intact HUB1 at the FLC is required for SPEN3 function in the formation of the FLC-derived antisense COOLAIR transcripts.
Asunto(s)
Proteínas de Arabidopsis , Regulación de la Expresión Génica de las Plantas , Histonas , ARN de Planta , Ubiquitina-Proteína Ligasas , Ubiquitinación , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Relojes Circadianos/genética , Relojes Circadianos/fisiología , Flores/genética , Flores/fisiología , Regulación de la Expresión Génica de las Plantas/genética , Regulación de la Expresión Génica de las Plantas/fisiología , Histonas/genética , Histonas/metabolismo , Dominios Proteicos/genética , Precursores del ARN/genética , Precursores del ARN/metabolismo , ARN de Planta/genética , ARN de Planta/metabolismo , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Ubiquitina-Proteína Ligasas/genética , Ubiquitina-Proteína Ligasas/metabolismo , Ubiquitinación/genética , Ubiquitinación/fisiologíaRESUMEN
The phytohormone cytokinin has been shown to affect many aspects of plant development ranging from the regulation of the shoot apical meristem to leaf senescence. However, some studies have reported contradictory effects of cytokinin on leaf physiology. Therefore cytokinin treatments cause both chlorosis and increased greening and both lead to decrease or increase in cell size. To elucidate this multifaceted role of cytokinin in leaf development, we have employed a system of temporal controls over the cytokinin pool and investigated the consequences of modulated cytokinin levels in the third leaf of Arabidopsis. We show that, at the cell proliferation phase, cytokinin is needed to maintain cell proliferation by blocking the transition to cell expansion and the onset of photosynthesis. Transcriptome profiling revealed regulation by cytokinin of a gene suite previously shown to affect cell proliferation and expansion and thereby a molecular mechanism by which cytokinin modulates a molecular network underlying the cellular responses. During the cell expansion phase, cytokinin stimulates cell expansion and differentiation. Consequently, a cytokinin excess at the cell expansion phase results in an increased leaf and rosette size fueled by higher cell expansion rate, yielding higher shoot biomass. Proteome profiling revealed the stimulation of primary metabolism by cytokinin, in line with an increased sugar content that is expected to increase turgor pressure, representing the driving force of cell expansion. Therefore, the developmental timing of cytokinin content fluctuations, together with a tight control of primary metabolism, is a key factor mediating transitions from cell proliferation to cell expansion in leaves.
Asunto(s)
Arabidopsis/fisiología , Citocininas/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Proteoma , Transducción de Señal , Transcriptoma , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Aumento de la Célula , Proliferación Celular , Ontología de Genes , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/fisiologíaRESUMEN
KEY MESSAGE: Here, we used a hxk1 mutant in the Col-0 background. We demonstrated that HXK1 regulates cell proliferation and expansion early during leaf development, and that HXK1 is involved in sucrose-induced leaf growth stimulation independent of GPT2. Furthermore, we identified KINγ as a novel HXK1-interacting protein. In the last decade, extensive efforts have been made to unravel the underlying mechanisms of plant growth control through sugar availability. Signaling by the conserved glucose sensor HEXOKINASE1 (HXK1) has been shown to exert both growth-promoting and growth-inhibitory effects depending on the sugar levels, the environmental conditions and the plant species. Here, we used a hxk1 mutant in the Col-0 background to investigate the role of HXK1 during leaf growth in more detail and show that it is affected in both cell proliferation and cell expansion early during leaf development. Furthermore, the hxk1 mutant is less sensitive to sucrose-induced cell proliferation with no significant increase in final leaf growth after transfer to sucrose. Early during leaf development, transfer to sucrose stimulates expression of GLUCOSE-6-PHOSPHATE/PHOSPHATE TRANSPORTER2 (GPT2) and represses chloroplast differentiation. However, in the hxk1 mutant GPT2 expression was still upregulated by transfer to sucrose although chloroplast differentiation was not affected, suggesting that GPT2 is not involved in HXK1-dependent regulation of leaf growth. Finally, using tandem affinity purification of protein complexes from cell cultures, we identified KINγ, a protein containing four cystathionine ß-synthase domains, as an interacting protein of HXK1.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimología , Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas , Hexoquinasa/metabolismo , Proteínas de Transporte de Monosacáridos/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Cloroplastos/metabolismo , Hexoquinasa/genética , Proteínas de Transporte de Monosacáridos/genética , Mutación , Hojas de la Planta/enzimología , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Proteínas Serina-Treonina Quinasas/genética , Plantones/enzimología , Plantones/genética , Plantones/crecimiento & desarrollo , Sacarosa/metabolismoRESUMEN
Droughts cause severe crop losses worldwide and climate change is projected to increase their prevalence in the future. Similar to the situation for many crops, the reference plant Arabidopsis thaliana (Ath) is considered drought-sensitive, whereas, as we demonstrate, its close relatives Arabidopsis lyrata (Aly) and Eutrema salsugineum (Esa) are drought-resistant. To understand the molecular basis for this plasticity we conducted a deep phenotypic, biochemical and transcriptomic comparison using developmentally matched plants. We demonstrate that Aly responds most sensitively to decreasing water availability with early growth reduction, metabolic adaptations and signaling network rewiring. By contrast, Esa is in a constantly prepared mode as evidenced by high basal proline levels, ABA signaling transcripts and late growth responses. The stress-sensitive Ath responds later than Aly and earlier than Esa, although its responses tend to be more extreme. All species detect water scarcity with similar sensitivity; response differences are encoded in downstream signaling and response networks. Moreover, several signaling genes expressed at higher basal levels in both Aly and Esa have been shown to increase water-use efficiency and drought resistance when overexpressed in Ath. Our data demonstrate contrasting strategies of closely related Brassicaceae to achieve drought resistance.
Asunto(s)
Adaptación Fisiológica , Brassicaceae/fisiología , Sequías , Ácido Abscísico/metabolismo , Brassicaceae/genética , Brassicaceae/crecimiento & desarrollo , Análisis por Conglomerados , Regulación de la Expresión Génica de las Plantas , Hojas de la Planta/crecimiento & desarrollo , Transducción de Señal , Especificidad de la Especie , Estrés Fisiológico , Transcriptoma/genética , AguaRESUMEN
Agrochemicals provide vast potential to improve plant productivity, because they are easy to implement at low cost while not being restricted by species barriers as compared with breeding strategies. Despite the general interest, only a few compounds with growth-promoting activity have been described so far. Here, we add cis-cinnamic acid (c-CA) to the small portfolio of existing plant growth stimulators. When applied at low micromolar concentrations to Arabidopsis roots, c-CA stimulates both cell division and cell expansion in leaves. Our data support a model explaining the increase in shoot biomass as the consequence of a larger root system, which allows the plant to explore larger areas for resources. The requirement of the cis-configuration for the growth-promoting activity of CA was validated by implementing stable structural analogs of both cis- and trans-CA in this study. In a complementary approach, we used specific light conditions to prevent cis/trans-isomerization of CA during the experiment. In both cases, the cis-form stimulated plant growth, whereas the trans-form was inactive. Based on these data, we conclude that c-CA is an appealing lead compound representing a novel class of growth-promoting agrochemicals. Unraveling the underlying molecular mechanism could lead to the development of innovative strategies for boosting plant biomass.
Asunto(s)
Cinamatos/farmacología , Desarrollo de la Planta/efectos de los fármacos , Arabidopsis/efectos de los fármacos , Arabidopsis/crecimiento & desarrollo , Ácidos Carboxílicos/farmacología , Cinamatos/química , Ciclopropanos/farmacología , Ácidos Indolacéticos/farmacología , Isomerismo , Nicotiana/efectos de los fármacos , Nicotiana/crecimiento & desarrolloRESUMEN
Plant growth and crop yield are negatively affected by a reduction in water availability. However, a clear understanding of how growth is regulated under nonlethal drought conditions is lacking. Recent advances in genomics, phenomics, and transcriptomics allow in-depth analysis of natural variation. In this study, we conducted a detailed screening of leaf growth responses to mild drought in a worldwide collection of Arabidopsis thaliana accessions. The genetic architecture of the growth responses upon mild drought was investigated by subjecting the different leaf growth phenotypes to genome-wide association mapping and by characterizing the transcriptome of young developing leaves. Although no major effect locus was found to be associated with growth in mild drought, the transcriptome analysis delivered further insight into the natural variation of transcriptional responses to mild drought in a specific tissue. Coexpression analysis indicated the presence of gene clusters that co-vary over different genetic backgrounds, among others a cluster of genes with important regulatory functions in the growth response to osmotic stress. It was found that the occurrence of a mild drought stress response in leaves can be inferred with high accuracy across accessions based on the expression profile of 283 genes. A genome-wide association study on the expression data revealed that trans regulation seems to be more important than cis regulation in the transcriptional response to environmental perturbations.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Sequías , Hojas de la Planta/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Perfilación de la Expresión Génica , Regulación de la Expresión Génica de las Plantas/genética , Regulación de la Expresión Génica de las Plantas/fisiología , Estudio de Asociación del Genoma Completo , Hojas de la Planta/genéticaRESUMEN
Although phytohormones such as gibberellins are essential for many conserved aspects of plant physiology and development, plants vary greatly in their responses to these regulatory compounds. Here, we use genetic perturbation of endogenous gibberellin levels to probe the extent of intraspecific variation in gibberellin responses in natural accessions of Arabidopsis (Arabidopsis thaliana). We find that these accessions vary greatly in their ability to buffer the effects of overexpression of GA20ox1, encoding a rate-limiting enzyme for gibberellin biosynthesis, with substantial differences in bioactive gibberellin concentrations as well as transcriptomes and growth trajectories. These findings demonstrate a surprising level of flexibility in the wiring of regulatory networks underlying hormone metabolism and signaling.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Giberelinas/metabolismo , Oxigenasas de Función Mixta/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas , Variación Genética , Oxigenasas de Función Mixta/genética , Reguladores del Crecimiento de las Plantas/metabolismo , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Plantas Modificadas GenéticamenteRESUMEN
Leaves are the plant's powerhouses, providing energy for all organs through sugar production during photosynthesis. However, sugars serve not only as a metabolic energy source for sink tissues but also as signaling molecules, affecting gene expression through conserved signaling pathways to regulate plant growth and development. Here, we describe an in vitro experimental assay, allowing one to alter the sucrose (Suc) availability during early Arabidopsis (Arabidopsis thaliana) leaf development, with the aim to identify the affected cellular and molecular processes. The transfer of seedlings to Suc-containing medium showed a profound effect on leaf growth by stimulating cell proliferation and postponing the transition to cell expansion. Furthermore, rapidly after transfer to Suc, mesophyll cells contained fewer and smaller plastids, which are irregular in shape and contain fewer starch granules compared with control mesophyll cells. Short-term transcriptional responses after transfer to Suc revealed the repression of well-known sugar-responsive genes and multiple genes encoded by the plastid, on the one hand, and up-regulation of a GLUCOSE-6-PHOSPHATE TRANSPORTER (GPT2), on the other hand. Mutant gpt2 seedlings showed no stimulation of cell proliferation and no repression of chloroplast-encoded transcripts when transferred to Suc, suggesting that GPT2 plays a critical role in the Suc-mediated effects on early leaf growth. Our findings, therefore, suggest that induction of GPT2 expression by Suc increases the import of glucose-6-phosphate into the plastids that would repress chloroplast-encoded transcripts, restricting chloroplast differentiation. Retrograde signaling from the plastids would then delay the transition to cell expansion and stimulate cell proliferation.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crecimiento & desarrollo , Cloroplastos/metabolismo , Proteínas de Transporte de Monosacáridos/metabolismo , Hojas de la Planta/crecimiento & desarrollo , Sacarosa/metabolismo , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proliferación Celular/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Células del Mesófilo/efectos de los fármacos , Proteínas de Transporte de Monosacáridos/genética , Mutación , Hojas de la Planta/citología , Hojas de la Planta/metabolismo , Plantones/efectos de los fármacos , Plantones/crecimiento & desarrollo , Sacarosa/farmacologíaRESUMEN
Strobilurins are an important class of agrochemical fungicides used throughout the world on a wide variety of crops as protection against fungal pathogens. In addition to this protective role, they are reported to also positively influence plant physiology. In this study, we analysed the effect of Stroby® WG, a commercially available fungicide consisting of 50% (w/w) kresoxim-methyl (KM) as active strobilurin compound, on Arabidopsis leaf growth. Treatment of seedlings with Stroby resulted in larger leaves due to an increase in cell number. Transcriptome analysis of Stroby-treated rosettes demonstrated an increased expression of genes involved in redox homeostasis, iron metabolism and sugar transport. Stroby treatment strongly induced the expression of the subgroup Ib basic helix-loop-helix (bHLH) transcription factors, which have a role in iron homeostasis under iron-limiting conditions. Single loss-of-function mutants of three bHLHs and their triple bhlh039, bhlh100 and bhlh101 mutant did not respond to Stroby treatment. Although iron and sucrose content was not affected, nitric oxide (NO) levels and nitrate reductase (NR) activity were significantly increased in Stroby-treated rosettes as compared with control plants. In conclusion, we suggest that the Stroby-mediated effects on growth depend on the increased expression of the subgroup Ib bHLHs and higher NO levels.
Asunto(s)
Arabidopsis/crecimiento & desarrollo , Hojas de la Planta/crecimiento & desarrollo , Estrobilurinas/farmacología , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Proliferación Celular/efectos de los fármacos , Regulación hacia Abajo/efectos de los fármacos , Perfilación de la Expresión Génica , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Ontología de Genes , Genes de Plantas , Hierro/metabolismo , Mutación/genética , Óxido Nítrico/metabolismo , Hojas de la Planta/efectos de los fármacos , Sacarosa/metabolismo , Regulación hacia Arriba/efectos de los fármacosRESUMEN
The transcriptional coactivator ANGUSTIFOLIA3 (AN3) stimulates cell proliferation during Arabidopsis thaliana leaf development, but the molecular mechanism is largely unknown. Here, we show that inducible nuclear localization of AN3 during initial leaf growth results in differential expression of important transcriptional regulators, including GROWTH REGULATING FACTORs (GRFs). Chromatin purification further revealed the presence of AN3 at the loci of GRF5, GRF6, CYTOKININ RESPONSE FACTOR2, CONSTANS-LIKE5 (COL5), HECATE1 (HEC1), and ARABIDOPSIS RESPONSE REGULATOR4 (ARR4). Tandem affinity purification of protein complexes using AN3 as bait identified plant SWITCH/SUCROSE NONFERMENTING (SWI/SNF) chromatin remodeling complexes formed around the ATPases BRAHMA (BRM) or SPLAYED. Moreover, SWI/SNF ASSOCIATED PROTEIN 73B (SWP73B) is recruited by AN3 to the promoters of GRF5, GRF3, COL5, and ARR4, and both SWP73B and BRM occupy the HEC1 promoter. Furthermore, we show that AN3 and BRM genetically interact. The data indicate that AN3 associates with chromatin remodelers to regulate transcription. In addition, modification of SWI3C expression levels increases leaf size, underlining the importance of chromatin dynamics for growth regulation. Our results place the SWI/SNF-AN3 module as a major player at the transition from cell proliferation to cell differentiation in a developing leaf.
Asunto(s)
Proteínas de Arabidopsis/fisiología , Arabidopsis/genética , Ensamble y Desensamble de Cromatina , Regulación de la Expresión Génica de las Plantas , Proteínas Represoras/fisiología , Adenosina Trifosfatasas/metabolismo , Arabidopsis/citología , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Sitios de Unión , Diferenciación Celular , Proliferación Celular , Proteínas Cromosómicas no Histona/metabolismo , Proteínas Cromosómicas no Histona/fisiología , Ciclina B/genética , Ciclina B/metabolismo , Genoma de Planta , Hojas de la Planta/citología , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Regiones Promotoras Genéticas , Proteínas Represoras/genética , Proteínas Represoras/metabolismoRESUMEN
Although the response of plants exposed to severe drought stress has been studied extensively, little is known about how plants adapt their growth under mild drought stress conditions. Here, we analyzed the leaf and rosette growth response of six Arabidopsis (Arabidopsis thaliana) accessions originating from different geographic regions when exposed to mild drought stress. The automated phenotyping platform WIWAM was used to impose stress early during leaf development, when the third leaf emerges from the shoot apical meristem. Analysis of growth-related phenotypes showed differences in leaf development between the accessions. In all six accessions, mild drought stress reduced both leaf pavement cell area and number without affecting the stomatal index. Genome-wide transcriptome analysis (using RNA sequencing) of early developing leaf tissue identified 354 genes differentially expressed under mild drought stress in the six accessions. Our results indicate the existence of a robust response over different genetic backgrounds to mild drought stress in developing leaves. The processes involved in the overall mild drought stress response comprised abscisic acid signaling, proline metabolism, and cell wall adjustments. In addition to these known severe drought-related responses, 87 genes were found to be specific for the response of young developing leaves to mild drought stress.
Asunto(s)
Arabidopsis/fisiología , Sequías , Ecotipo , Hojas de la Planta/fisiología , Estrés Fisiológico , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Pared Celular/metabolismo , Perfilación de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Ontología de Genes , Redes Reguladoras de Genes , Genes de Plantas , Fenotipo , Hojas de la Planta/anatomía & histología , Plantones/crecimiento & desarrolloRESUMEN
Although quantitative characterization of growth phenotypes is of key importance for the understanding of essential networks driving plant growth, the majority of growth-related genes are still being identified based on qualitative visual observations and/or single-endpoint quantitative measurements. We developed an in vitro growth imaging system (IGIS) to perform time-resolved analysis of rosette growth. In this system, Arabidopsis plants are grown in Petri dishes mounted on a rotating disk, and images of each plate are taken on an hourly basis. Automated image analysis was developed in order to obtain several growth-related parameters, such as projected rosette area, rosette relative growth rate, compactness and stockiness, over time. To illustrate the use of the platform and the resulting data, we present the results for the growth response of Col-0 plants subjected to three mild stress conditions. Although the reduction in rosette area was relatively similar at 19 days after stratification, the time-lapse analysis demonstrated that plants react differently to salt, osmotic and oxidative stress. The rosette area was altered at various time points during development, and leaf movement and shape parameters were also affected differently. We also used the IGIS to analyze in detail the growth behavior of mutants with enhanced leaf size. Analysis of several growth-related parameters over time in these mutants revealed several specificities in growth behavior, underlining the high complexity of leaf growth coordination. These results demonstrate that time-resolved imaging of in vitro rosette growth generates a better understanding of growth phenotypes than endpoint measurements.
Asunto(s)
Arabidopsis/crecimiento & desarrollo , Procesamiento de Imagen Asistido por Computador/métodos , Arabidopsis/genética , Arabidopsis/efectos de la radiación , Genotipo , Procesamiento de Imagen Asistido por Computador/instrumentación , Luz , Mutación , Fenotipo , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/efectos de la radiación , Plantas Modificadas Genéticamente , Plantones/genética , Plantones/crecimiento & desarrollo , Plantones/efectos de la radiación , Factores de TiempoRESUMEN
In multicellular organisms, morphogenesis relies on a strict coordination in time and space of cell proliferation and differentiation. In contrast to animals, plant development displays continuous organ formation and adaptive growth responses during their lifespan relying on a tight coordination of cell proliferation. How developmental signals interact with the plant cell-cycle machinery is largely unknown. Here, we characterize plant A2-type cyclins, a small gene family of mitotic cyclins, and show how they contribute to the fine-tuning of local proliferation during plant development. Moreover, the timely repression of CYCA2;3 expression in newly formed guard cells is shown to require the stomatal transcription factors FOUR LIPS/MYB124 and MYB88, providing a direct link between developmental programming and cell-cycle exit in plants. Thus, transcriptional downregulation of CYCA2s represents a critical mechanism to coordinate proliferation during plant development.
Asunto(s)
Proteínas de Arabidopsis/fisiología , Arabidopsis/citología , Ciclina A2/fisiología , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Arabidopsis/genética , Proteínas de Arabidopsis/biosíntesis , Proteínas de Arabidopsis/genética , Ciclo Celular , División Celular , Ciclina A2/biosíntesis , Ciclina A2/genética , Regulación hacia Abajo , Morfogénesis , Especificidad de Órganos , Hojas de la Planta/metabolismo , Raíces de Plantas/metabolismo , Poliploidía , Factores de Transcripción/fisiologíaRESUMEN
Auxin transport, which is mediated by specialized influx and efflux carriers, plays a major role in many aspects of plant growth and development. AUXIN1 (AUX1) has been demonstrated to encode a high-affinity auxin influx carrier. In Arabidopsis thaliana, AUX1 belongs to a small multigene family comprising four highly conserved genes (i.e., AUX1 and LIKE AUX1 [LAX] genes LAX1, LAX2, and LAX3). We report that all four members of this AUX/LAX family display auxin uptake functions. Despite the conservation of their biochemical function, AUX1, LAX1, and LAX3 have been described to regulate distinct auxin-dependent developmental processes. Here, we report that LAX2 regulates vascular patterning in cotyledons. We also describe how regulatory and coding sequences of AUX/LAX genes have undergone subfunctionalization based on their distinct patterns of spatial expression and the inability of LAX sequences to rescue aux1 mutant phenotypes, respectively. Despite their high sequence similarity at the protein level, transgenic studies reveal that LAX proteins are not correctly targeted in the AUX1 expression domain. Domain swapping studies suggest that the N-terminal half of AUX1 is essential for correct LAX localization. We conclude that Arabidopsis AUX/LAX genes encode a family of auxin influx transporters that perform distinct developmental functions and have evolved distinct regulatory mechanisms.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Ácidos Indolacéticos/metabolismo , Proteínas de Transporte de Membrana/metabolismo , Arabidopsis/citología , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Transporte Biológico , Tipificación del Cuerpo , Cotiledón/citología , Cotiledón/genética , Cotiledón/crecimiento & desarrollo , Cotiledón/metabolismo , Técnicas de Inactivación de Genes , Proteínas de Transporte de Membrana/genética , Familia de Multigenes , Mutagénesis Insercional , Fenotipo , Raíces de Plantas/citología , Raíces de Plantas/genética , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Haz Vascular de Plantas/citología , Haz Vascular de Plantas/genética , Haz Vascular de Plantas/crecimiento & desarrollo , Haz Vascular de Plantas/metabolismo , Plantas Modificadas Genéticamente , Plantones/citología , Plantones/genética , Plantones/crecimiento & desarrollo , Plantones/metabolismoRESUMEN
OBJECTIVES: To study cyclists' share of transport modes (modal share) and single-bicycle crashes (SBCs) in different countries in order to investigate if the proportion of cyclist injuries resulting from SBCs is affected by variation in modal share. METHODS: A literature search identified figures (largely from western countries) on SBC casualties who are fatally injured, hospitalised or treated at an emergency department. Correlation and regression analyses were used to investigate how bicycle modal share is related to SBCs. RESULTS: On average, 17% of fatal injuries to cyclists are caused by SBCs. Different countries show a range of values between 5% and 30%. Between 60% and 95% of cyclists admitted to hospitals or treated at emergency departments are victims of SBCs. The proportion of all injured cyclists who are injured in SBCs is unrelated to the share of cycling in the modal split. The share of SBC casualties among the total number of road crash casualties increases proportionally less than the increase in bicycle modal share. CONCLUSIONS: While most fatal injuries among cyclists are due to motor vehicle-bicycle crashes, most hospital admissions and emergency department attendances result from SBCs. As found in previous studies of cyclists injured in collisions, this study found that the increase in the number of SBC casualties is proportionally less than the increase in bicycle modal share.
Asunto(s)
Accidentes de Tránsito/estadística & datos numéricos , Ciclismo/lesiones , Servicio de Urgencia en Hospital/estadística & datos numéricos , Hospitalización/estadística & datos numéricos , Humanos , Análisis de RegresiónRESUMEN
Endoreduplication is the process where a cell replicates its genome without mitosis and cytokinesis, often followed by cell differentiation. This alternative cell cycle results in various levels of endoploidy, reaching 4× or higher one haploid set of chromosomes. Endoreduplication is found in animals and is widespread in plants, where it plays a major role in cellular differentiation and plant development. Here, we show that variation in endoreduplication between Arabidopsis thaliana accessions Columbia-0 and Kashmir is controlled by two major quantitative trait loci, ENDO-1 and ENDO-2. A local candidate gene association analysis in a set of 87 accessions, combined with expression analysis, identified CYCD5;1 as the most likely candidate gene underlying ENDO-2, operating as a rate-determining factor of endoreduplication. In accordance, both the overexpression and silencing of CYCD5;1 were effective in changing DNA ploidy levels, confirming CYCD5;1 to be a previously undescribed quantitative trait gene underlying endoreduplication in Arabidopsis.
Asunto(s)
Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/fisiología , Arabidopsis/genética , Alelos , Mapeo Cromosómico , Cromosomas de las Plantas/genética , Genes de Plantas , Genotipo , Haplotipos , Cinética , Escala de Lod , Modelos Genéticos , Fenotipo , Fenómenos Fisiológicos de las Plantas , Ploidias , Polimorfismo Genético , Sitios de Carácter CuantitativoRESUMEN
The anaphase-promoting complex/cyclosome (APC/C) is a large multiprotein E3 ubiquitin ligase involved in ubiquitin-dependent proteolysis of key cell cycle regulatory proteins, including the destruction of mitotic cyclins at the metaphase-to-anaphase transition. Despite its importance, the role of the APC/C in plant cells and the regulation of its activity during cell division remain poorly understood. Here, we describe the identification of a plant-specific negative regulator of the APC/C complex, designated SAMBA. In Arabidopsis thaliana, SAMBA is expressed during embryogenesis and early plant development and plays a key role in organ size control. Samba mutants produced larger seeds, leaves, and roots, which resulted from enlarged root and shoot apical meristems, and, additionally, they had a reduced fertility attributable to a hampered male gametogenesis. Inactivation of SAMBA stabilized A2-type cyclins during early development. Our data suggest that SAMBA regulates cell proliferation during early development by targeting CYCLIN A2 for APC/C-mediated proteolysis.
Asunto(s)
Arabidopsis/genética , Arabidopsis/metabolismo , Ciclina A/química , Mutación , Complejos de Ubiquitina-Proteína Ligasa/fisiología , Secuencia de Aminoácidos , Ciclosoma-Complejo Promotor de la Anafase , Ciclo Celular , Regulación de la Expresión Génica de las Plantas , Modelos Biológicos , Modelos Genéticos , Datos de Secuencia Molecular , Fenotipo , Hojas de la Planta/metabolismo , Proteínas de Plantas/metabolismo , Polen/metabolismo , Homología de Secuencia de Aminoácido , Complejos de Ubiquitina-Proteína Ligasa/genéticaRESUMEN
Leaf growth is a complex developmental process that is continuously fine-tuned by the environment. Various abiotic stresses, including mild drought stress, have been shown to inhibit leaf growth in Arabidopsis (Arabidopsis thaliana), but the underlying mechanisms remain largely unknown. Here, we identify the redundant Arabidopsis transcription factors ETHYLENE RESPONSE FACTOR5 (ERF5) and ERF6 as master regulators that adapt leaf growth to environmental changes. ERF5 and ERF6 gene expression is induced very rapidly and specifically in actively growing leaves after sudden exposure to osmotic stress that mimics mild drought. Subsequently, enhanced ERF6 expression inhibits cell proliferation and leaf growth by a process involving gibberellin and DELLA signaling. Using an ERF6-inducible overexpression line, we demonstrate that the gibberellin-degrading enzyme GIBBERELLIN 2-OXIDASE6 is transcriptionally induced by ERF6 and that, consequently, DELLA proteins are stabilized. As a result, ERF6 gain-of-function lines are dwarfed and hypersensitive to osmotic stress, while the growth of erf5erf6 loss-of-function mutants is less affected by stress. Besides its role in plant growth under stress, ERF6 also activates the expression of a plethora of osmotic stress-responsive genes, including the well-known stress tolerance genes STZ, MYB51, and WRKY33. Interestingly, activation of the stress tolerance genes by ERF6 occurs independently from the ERF6-mediated growth inhibition. Together, these data fit into a leaf growth regulatory model in which ERF5 and ERF6 form a missing link between the previously observed stress-induced 1-aminocyclopropane-1-carboxylic acid accumulation and DELLA-mediated cell cycle exit and execute a dual role by regulating both stress tolerance and growth inhibition.