RESUMEN
Plants respond to gravitational force through directional growth along the gravity vector. Although auxin is the central component of the root graviresponse, it works in concert with other plant hormones. Here, we show that the folate precursor para-aminobenzoic acid (PABA) is a key modulator of the auxin-ethylene interplay during root gravitropism in Arabidopsis (Arabidopsis thaliana). In gravistimulated roots, PABA promotes an asymmetric auxin response, which causes the asymmetric growth responsible for root curvature. This activity requires the auxin response transcription factors AUXIN RESPONSE FACTOR7 (ARF7) and ARF19 as well as ethylene biosynthesis and signaling, indicating that PABA activity requires both auxin and ethylene pathways. Similar to ethylene, exogenous PABA reverses the agravitropic root growth of the auxin transport mutant pin-formed2 (pin2) and the auxin biosynthetic double mutant with loss of function of weak ethylene insensitive (wei) genes, wei8wei2, but not the pin2wei8wei2 triple mutant. This finding suggests that PABA regulates the ethylene-dependent reciprocal compensation between auxin transport and biosynthesis. Furthermore, manipulation of endogenous free PABA levels by modulating the expression of the gene encoding its glucosylation enzyme, UDP-GLYCOSYL TRANSFERASE75B1, impacts the root graviresponse, suggesting that endogenous free PABA levels may play a crucial role in modulating the auxin-ethylene cross talk necessary for root gravitropism.
Asunto(s)
Ácido 4-Aminobenzoico/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiología , Etilenos/metabolismo , Gravitropismo , Ácidos Indolacéticos/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Transporte Biológico , Glucosiltransferasas/genética , Glucosiltransferasas/metabolismo , Gravitación , Fenotipo , Raíces de Plantas/genética , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/fisiología , Plantones/genética , Plantones/crecimiento & desarrollo , Plantones/fisiología , Transducción de Señal , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Auxin gradients are sustained by series of influx and efflux carriers whose subcellular localization is sensitive to both exogenous and endogenous factors. Recently the localization of the Arabidopsis thaliana auxin efflux carrier PIN-FORMED (PIN) 6 was reported to be tissue-specific and regulated through unknown mechanisms. Here, we used genetic, molecular and pharmacological approaches to characterize the molecular mechanism(s) controlling the subcellular localization of PIN6. PIN6 localizes to endomembrane domains in tissues with low PIN6 expression levels such as roots, but localizes at the plasma membrane (PM) in tissues with increased PIN6 expression such as the inflorescence stem and nectary glands. We provide evidence that this dual localization is controlled by PIN6 phosphorylation and demonstrate that PIN6 is phosphorylated by mitogen-activated protein kinases (MAPKs) MPK4 and MPK6. The analysis of transgenic plants expressing PIN6 at PM or in endomembrane domains reveals that PIN6 subcellular localization is critical for Arabidopsis inflorescence stem elongation post-flowering (bolting). In line with a role for PIN6 in plant bolting, inflorescence stems elongate faster in pin6 mutant plants than in wild-type plants. We propose that PIN6 subcellular localization is under the control of developmental signals acting on tissue-specific determinants controlling PIN6-expression levels and PIN6 phosphorylation.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiología , Membrana Celular/metabolismo , Proteínas de Transporte de Membrana/metabolismo , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Membrana Celular/efectos de los fármacos , Retículo Endoplásmico/efectos de los fármacos , Retículo Endoplásmico/metabolismo , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Interacciones Hidrofóbicas e Hidrofílicas , Hipocótilo/efectos de los fármacos , Hipocótilo/metabolismo , Ácidos Indolacéticos/farmacología , Inflorescencia/efectos de los fármacos , Inflorescencia/metabolismo , Mutación con Pérdida de Función , Meristema/efectos de los fármacos , Meristema/metabolismo , Fosforilación/efectos de los fármacos , Fosfotreonina/metabolismo , Plantas Modificadas Genéticamente , Transporte de Proteínas/efectos de los fármacos , Fracciones Subcelulares/metabolismoRESUMEN
Arbuscular mycorrhizas (AM) are the most common symbiotic associations between a plant's root compartment and fungi. They provide nutritional benefit (mostly inorganic phosphate [Pi]), leading to improved growth, and nonnutritional benefits, including defense responses to environmental cues throughout the host plant, which, in return, delivers carbohydrates to the symbiont. However, how transcriptional and metabolic changes occurring in leaves of AM plants differ from those induced by Pi fertilization is poorly understood. We investigated systemic changes in the leaves of mycorrhized Medicago truncatula in conditions with no improved Pi status and compared them with those induced by high-Pi treatment in nonmycorrhized plants. Microarray-based genome-wide profiling indicated up-regulation by mycorrhization of genes involved in flavonoid, terpenoid, jasmonic acid (JA), and abscisic acid (ABA) biosynthesis as well as enhanced expression of MYC2, the master regulator of JA-dependent responses. Accordingly, total anthocyanins and flavonoids increased, and most flavonoid species were enriched in AM leaves. Both the AM and Pi treatments corepressed iron homeostasis genes, resulting in lower levels of available iron in leaves. In addition, higher levels of cytokinins were found in leaves of AM- and Pi-treated plants, whereas the level of ABA was increased specifically in AM leaves. Foliar treatment of nonmycorrhized plants with either ABA or JA induced the up-regulation of MYC2, but only JA also induced the up-regulation of flavonoid and terpenoid biosynthetic genes. Based on these results, we propose that mycorrhization and Pi fertilization share cytokinin-mediated improved shoot growth, whereas enhanced ABA biosynthesis and JA-regulated flavonoid and terpenoid biosynthesis in leaves are specific to mycorrhization.
Asunto(s)
Glomeromycota/fisiología , Medicago truncatula/fisiología , Micorrizas/fisiología , Reguladores del Crecimiento de las Plantas/metabolismo , Proteínas de Plantas/metabolismo , Metabolismo Secundario , Ácido Abscísico/metabolismo , Ciclopentanos/metabolismo , Flavonoides/metabolismo , Regulación de la Expresión Génica de las Plantas , Medicago truncatula/genética , Medicago truncatula/microbiología , Oxilipinas/metabolismo , Fosfatos/metabolismo , Hojas de la Planta/genética , Hojas de la Planta/microbiología , Hojas de la Planta/fisiología , Proteínas de Plantas/genética , Simbiosis , Terpenos/metabolismo , Regulación hacia ArribaRESUMEN
The Arabidopsis phosphate transporter PHT4;1 was previously localized to the chloroplast thylakoid membrane. Here we investigated the physiological consequences of the absence of PHT4;1 for photosynthesis and plant growth. In standard growth conditions, two independent Arabidopsis knockout mutant lines displayed significantly reduced leaf size and biomass but normal phosphorus content. When mutants were grown in high-phosphate conditions, the leaf phosphorus levels increased and the growth phenotype was suppressed. Photosynthetic measurements indicated that in the absence of PHT4;1 stromal phosphate was reduced to levels that limited ATP synthase activity. This resulted in reduced CO2 fixation and accumulation of soluble sugars, limiting plant growth. The mutants also displayed faster induction of non-photochemical quenching than the wild type, in line with the increased contribution of ΔpH to the proton-motive force across thylakoids. Small-angle neutron scattering showed a smaller lamellar repeat distance, whereas circular dichroism spectroscopy indicated a perturbed long-range order of photosystem II (PSII) complexes in the mutant thylakoids. The absence of PHT4;1 did not alter the PSII repair cycle, as indicated by wild-type levels of phosphorylation of PSII proteins, inactivation and D1 protein degradation. Interestingly, the expression of genes for several thylakoid proteins was downregulated in the mutants, but the relative levels of the corresponding proteins were either not affected or could not be discerned. Based on these data, we propose that PHT4;1 plays an important role in chloroplast phosphate compartmentation and ATP synthesis, which affect plant growth. It also maintains the ionic environment of thylakoids, which affects the macro-organization of complexes and induction of photoprotective mechanisms.
Asunto(s)
Adenosina Trifosfato/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Proteínas de Transporte de Fosfato/metabolismo , Fosfatos/metabolismo , Tilacoides/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Transporte de Fosfato/genética , Fotosíntesis/genética , Fotosíntesis/fisiología , Complejo de Proteína del Fotosistema II/genética , Complejo de Proteína del Fotosistema II/metabolismoRESUMEN
The continuous growth of roots depends on their ability to maintain a balanced ratio between cell production and cell differentiation at the tip. This process is regulated by the hormonal balance of cytokinin and auxin. However, other important regulators, such as plant folates, also play a regulatory role. In this study, we investigated the impact of the folate precursor para-aminobenzoic acid (PABA) on root development. Using pharmacological, genetic, and imaging approaches, we show that the growth of Arabidopsis thaliana roots is repressed by either supplementing the growth medium with PABA or overexpressing the PABA synthesis gene GAT-ADCS. This is associated with a smaller root meristem consisting of fewer cells. Conversely, reducing the levels of free root endogenous PABA results in longer roots with extended meristems. We provide evidence that PABA represses Arabidopsis root growth in a folate-independent manner and likely acts through two mechanisms: (i) the G2/M transition of cell division in the root apical meristem and (ii) promoting premature cell differentiation in the transition zone. These data collectively suggest that PABA plays a role in Arabidopsis root growth at the intersection between cell division and cell differentiation.
RESUMEN
Lateral roots are initiated postembryonically in response to environmental cues, enabling plants to explore efficiently their underground environment. However, the mechanisms by which the environment determines the position of lateral root formation are unknown. In this study, we demonstrate that in Arabidopsis thaliana lateral root initiation can be induced mechanically by either gravitropic curvature or by the transient bending of a root by hand. The plant hormone auxin accumulates at the site of lateral root induction before a primordium starts to form. Here we describe a subcellular relocalization of PIN1, an auxin transport protein, in a single protoxylem cell in response to gravitropic curvature. This relocalization precedes auxin-dependent gene transcription at the site of a new primordium. Auxin-dependent nuclear signaling is necessary for lateral root formation; arf7/19 double knock-out mutants normally form no lateral roots but do so upon bending when the root tip is removed. Signaling through arf7/19 can therefore be bypassed by root bending. These data support a model in which a root-tip-derived signal acts on downstream signaling molecules that specify lateral root identity.
Asunto(s)
Arabidopsis/crecimiento & desarrollo , Gravitropismo , Meristema/crecimiento & desarrollo , Raíces de Plantas/crecimiento & desarrollo , Transducción de Señal/fisiología , Arabidopsis/anatomía & histología , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Ácidos Indolacéticos/metabolismo , Proteínas de Transporte de Membrana/genética , Proteínas de Transporte de Membrana/metabolismo , Meristema/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Raíces de Plantas/anatomía & histología , Raíces de Plantas/metabolismo , Brotes de la Planta/anatomía & histología , Brotes de la Planta/crecimiento & desarrollo , Brotes de la Planta/metabolismo , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Estrés MecánicoRESUMEN
In variable light environments, plants adjust light use in photosynthetic electron transport and photoprotective dissipation in the thylakoid membrane. In this respect, roles of the K+/H+ antiporter KEA3, the Cl- channel/transporter CLCe and the voltage-dependent Cl- channel VCCN1 have been unraveled in Arabidopsis thaliana. Here we report that they independently adjust photosynthesis on the basis of analyses using single and higher order loss-of-function mutants. In short experiments of photosynthetic response on transition from dark to low light, we reveal a sequential functioning of VCCN1 and CLCe in the activation of photoprotection and of KEA3 in its downregulation to a low steady state while adjusting the electron transport. On transition from low to high light, VCCN1 accelerates the activation of photoprotection, whereas KEA3 slows it down on transition from high to low light. Based on parallel electrochromic band shift measurements, the mechanism behind is that VCCN1 builds up a pH gradient across the thylakoid membrane, whereas KEA3 dissipates this gradient, which affects photoprotection. CLCe regulates photosynthesis by a pH-independent mechanism likely involving Cl- homeostasis. Nevertheless, all genotypes grow well in alternating high and low light. Taken together, the three studied ion channels/transporters function independently in adjusting photosynthesis to the light environment.
Asunto(s)
Canales de Cloruro/metabolismo , Fotosíntesis , Proteínas de Plantas/metabolismo , Canales de Potasio/metabolismo , Clorofila/metabolismo , Clorofila A/metabolismo , Fluorescencia , Luz , Modelos Biológicos , Fenotipo , Tilacoides/metabolismo , Tilacoides/ultraestructuraRESUMEN
Reticulons are proteins that have been found predominantly associated with the endoplasmic reticulum in yeast and mammalian cells. While their functions are still poorly understood, recent findings suggest that they participate in the shaping of the tubular endoplamic reticulum (ER). Although reticulon-like proteins have been identified in plants, very little is known about their cellular localization and functions. Here, we characterized the reticulon-like protein family of Arabidopsis thaliana. Three subfamilies can be distinguished on the basis of structural organization and sequence homology. We investigated the subcellular localization of two members of the largest subfamily, i.e. AtRTNLB2 and AtRTNLB4, using fluorescent protein tags. The results demonstrate for the first time that plant reticulon-like proteins are associated with the ER. Both AtRTNLB proteins are located in the tubular ER but AtRTNLB4 is also found in the lamellar ER cisternae, and in ER tubules in close association with the chloroplasts. Similarity in protein structure and subcellular localization between AtRTNLB2 and mammalian reticulons suggests that they could assume similar basic functions inside the cell.
Asunto(s)
Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/metabolismo , Arabidopsis/química , Arabidopsis/metabolismo , Retículo Endoplásmico/metabolismo , Secuencia de Aminoácidos , Arabidopsis/genética , Proteínas de Arabidopsis/clasificación , Proteínas de Arabidopsis/genética , Secuencia Conservada , Datos de Secuencia Molecular , Filogenia , Epidermis de la Planta/metabolismo , Alineación de Secuencia , Homología de Secuencia de AminoácidoRESUMEN
Chloride ions can be translocated across cell membranes through Cl(-) channels or Cl(-)/H(+) exchangers. The thylakoid-located member of the Cl(-) channel CLC family in Arabidopsis thaliana (AtCLCe) was hypothesized to play a role in photosynthetic regulation based on the initial photosynthetic characterization of clce mutant lines. The reduced nitrate content of Arabidopsis clce mutants suggested a role in regulation of plant nitrate homeostasis. In this study, we aimed to further investigate the role of AtCLCe in the regulation of ion homeostasis and photosynthetic processes in the thylakoid membrane. We report that the size and composition of proton motive force were mildly altered in two independent Arabidopsis clce mutant lines. Most pronounced effects in the clce mutants were observed on the photosynthetic electron transport of dark-adapted plants, based on the altered shape and associated parameters of the polyphasic OJIP kinetics of chlorophyll a fluorescence induction. Other alterations were found in the kinetics of state transition and in the macro-organization of photosystem II supercomplexes, as indicated by circular dichroism measurements. Pre-treatment with KCl but not with KNO3 restored the wild-type photosynthetic phenotype. Analyses by transmission electron microscopy revealed a bow-like arrangement of the thylakoid network and a large thylakoid-free stromal region in chloroplast sections from the dark-adapted clce plants. Based on these data, we propose that AtCLCe functions in Cl(-) homeostasis after transition from light to dark, which affects chloroplast ultrastructure and regulation of photosynthetic electron transport.