OCP3 is an important modulator of NPR1-mediated jasmonic acid-dependent induced defenses in Arabidopsis

<p>Abstract</p> <p>Background</p> <p>Upon appropriate stimulation, plants increase their level of resistance against future pathogen attack. This phenomenon, known as induced resistance, presents an adaptive advantage due to its reduced fitness costs and its systemic and broad-spectrum nature. In <it>Arabidopsis</it>, different types of induced resistance have been defined based on the signaling pathways involved, particularly those dependent on salicylic acid (SA) and/or jasmonic acid (JA).</p> <p>Results</p> <p>Here, we have assessed the implication of the transcriptional regulator OCP3 in SA- and JA-dependent induced defenses. Through a series of double mutant analyses, we conclude that SA-dependent defense signaling does not require OCP3. However, we found that <it>ocp3 </it>plants are impaired in a <it>Pseudomonas fluorescens </it>WCS417r-triggered induced systemic resistance (ISR) against both <it>Pseudomonas syrinagae </it>DC3000 and <it>Hyaloperonospora arabidopsidis</it>, and we show that this impairment is not due to a defect in JA-perception. Likewise, exogenous application of JA failed to induce defenses in <it>ocp3 </it>plants. In addition, we provide evidence showing that the over-expression of an engineered cytosolic isoform of the disease resistance regulator NPR1 restores the impaired JA-induced disease resistance in <it>ocp3 </it>plants.</p> <p>Conclusions</p> <p>Our findings point to a model in which OCP3 may modulate the nucleocytosolic function of NPR1 in the regulation of JA-dependent induced defense responses.</p

ABA inhibits myristoylation and induces shuttling of the RGLG1 E3 ligase to promote nuclear degradation of PP2CA

[EN] Hormone- and stress-induced shuttling of signaling or regulatory proteins is an important cellular mechanism to modulate hormone signaling and cope with abiotic stress. Hormone-induced ubiquitination plays a crucial role to determine half-life of key negative regulators of hormone signaling. For ABA signaling, degradation of clade A PP2Cs, such as PP2CA or ABI1, is a complementary mechanism to PYR/PYL/RCAR-mediated inhibition of PP2C activity. ABA promotes the degradation of PP2CA through the RGLG1 E3 ligase, although it is not known how ABA enhances the interaction of RGLG1 with PP2CA given they are predominantly found in plasma membrane and nucleus, respectively. We demonstrate that ABA modifies the subcellular localization of RGLG1 and promotes nuclear interaction with PP2CA. We found RGLG1 is myristoylated in vivo, which facilitates its attachment to plasma membrane. ABA inhibits myristoylation of RGLG1 through downregulation of Nmyristoyltransferase1 (NMT1) and promotes nuclear translocation of RGLG1 in a cycloheximide-insensitive manner. Enhanced nuclear recruitment of the E3 ligase was also promoted by increasing PP2CA protein levels and the formation of RGLG1-receptor-phosphatase complexes. We show that RGLG1Gly2Ala -mutated in the Nterminal myristoylation site- shows constitutive nuclear localization and causes enhanced response to ABA and salt/osmotic stress. RGLG1/5 can interact with certain monomeric ABA receptors, which facilitates the formation of nuclear complexes such as RGLG1-PP2CA-PYL8. In summary, we provide evidence that an E3 ligase can dynamically re-localize in response to both ABA and increased levels of its target, which reveals a mechanism to explain how ABA enhances RGLG1-PP2CA interaction and hence PP2CA degradation.Work in P.L.R.'s laboratory was supported by the Ministerio de Ciencia e Innovacion, Fondo Europeo de Desarrollo Regional and Consejo Superior de Investigaciones Cientificas through grants BIO2014-52537-R and BIO2017-82503-R. This work was also funded by grants from the Deutsche Forschungsgemeinschaft (DFG) Ku931/4-1 to J. K., and BA4742/1-2 to O.B. B.B. was funded by Programa VALi+ d GVA APOSTD/2017/039. J.J. was supported by an FPI contract from MINECOBelda Palazón, B.; Julian, J.; Coego, A.; Wu, Q.; Zhang, X.; Batistic, O.; Alquraishi, SA.... (2019). ABA inhibits myristoylation and induces shuttling of the RGLG1 E3 ligase to promote nuclear degradation of PP2CA. 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Biostimulant activity of Galaxaura rugosa seaweed extracts against water deficit stress in tomato seedlings involves activation of ABA signaling

Water scarcity is a serious constraint for agriculture, and global warming and climate change can exacerbate it in many areas. Therefore, sustainable approaches must be implemented to deal with current and future water scarcity scenarios. Genetic and chemical approaches are being applied to manage this limitation and maintain crop yields. In particular, biostimulants obtained from natural sources such as marine algae are promising aids for coping with water deficit stress in agriculture. Here we present a bioprospection study of extracts of the macroalgae Bonnemaisonia hamifera, Galaxaura rugosa, Dasycladus vermicularis, Ulva clathrata, Cystoseira foeniculacea, Cystoseira humilis, Lobophora dagamae, Colpomenia sinuosa and Halopteris scoparia from the north coast of Tenerife, in the Canary Islands. The aqueous extracts of Bonnemaisonia hamifera, Galaxaura rugosa, Dasycladus vermicularis and Cystoseira humilis show biostimulant activity against water deficit stress in tomato seedlings under controlled conditions, providing higher tolerance than the mock-treated control. The Galaxaura rugosa extract showed the highest biostimulant activity against water deficit stress. We demonstrate that this positive effect involves the activation of the abscisic acid (ABA) pathway in Arabidopsis thaliana (arabidopsis) and Solanum lycopersicum (tomato). Application of G. rugosa extract to the root system by drenching tomato seedlings subjected to water deficit leads to improved CO2 assimilation and water use efficiency (WUEp), compared to mock-treated plants. These results highlight a new potential seaweed source of substances with osmoprotectant properties, useful for biostimulant development. Future studies may provide further insight into which components of the seaweed extract induce activation of the ABA pathway

Structure-guided engineering of a receptor-agonist pair for inducible activation of the ABA adaptive response to drought

Strategies to activate abscisic acid (ABA) receptors and boost ABA signaling by small molecules that act as ABA receptor agonists are promising biotechnological tools to enhance plant drought tolerance. Protein structures of crop ABA receptors might require modifications to improve recognition of chemical ligands, which in turn can be optimized by structural information. Through structure-based targeted design, we have combined chemical and genetic approaches to generate an ABA receptor agonist molecule (iSB09) and engineer a CsPYL1 ABA receptor, named CsPYL15m, which efficiently binds iSB09. This optimized receptor-agonist pair leads to activation of ABA signaling and marked drought tolerance. No constitutive activation of ABA signaling and hence growth penalty was observed in transformed Arabidopsis thaliana plants. Therefore, conditional and efficient activation of ABA signaling was achieved through a chemical-genetic orthogonal approach based on iterative cycles of ligand and receptor optimization driven by the structure of ternary receptor-ligand-phosphatase complexes

Abscisic acid mimic-fluorine derivative 4 alleviates water deficit stress by regulating ABA-responsive genes, proline accumulation, CO2 assimilation, water use efficiency and better nutrient uptake in tomato plants

Water deficit represents a serious limitation for agriculture and both genetic and chemical approaches are being used to cope with this stress and maintain plant yield. Next-generation agrochemicals that control stomatal aperture are promising for controlling water use efficiency. For example, chemical control of abscisic acid (ABA) signaling through ABA-receptor agonists is a powerful method to activate plant adaptation to water deficit. Such agonists are molecules able to bind and activate ABA receptors and, although their development has experienced significant advances in the last decade, few translational studies have been performed in crops. Here, we describe protection by the ABA mimic-fluorine derivative 4 (AMF4) agonist of the vegetative growth in tomato plants subjected to water restriction. Photosynthesis in mock-treated plants is markedly impaired under water deficit conditions, whereas AMF4 treatment notably improves CO2 assimilation, the relative plant water content and growth. As expected for an antitranspirant molecule, AMF4 treatment diminishes stomatal conductance and transpiration in the first phase of the experiment; however, when photosynthesis declines in mock-treated plants as stress persists, higher photosynthetic and transpiration parameters are recorded in agonist-treated plants. Additionally, AMF4 increases proline levels over those achieved in mock-treated plants in response to water deficit. Thus water deficit and AMF4 cooperate to upregulate P5CS1 through both ABA-independent and ABA-dependent pathways, and therefore, higher proline levels are produced Finally, analysis of macronutrients reveals higher levels of Ca, K and Mg in AMF4- compared to mock-treated plants subjected to water deficit. Overall, these physiological analyses reveal a protective effect of AMF4 over photosynthesis under water deficit and enhanced water use efficiency after agonist treatment. In summary, AMF4 treatment is a promising approach for farmers to protect the vegetative growth of tomatoes under water deficit stress

Nitric oxide sensing in plants is mediated by proteolytic control of group VII ERF transcription factors

Nitric oxide (NO) is an important signaling compound in prokaryotes and eukaryotes. In plants, NO regulates critical developmental transitions and stress responses. Here, we identify a mechanism for NO sensing that coordinates responses throughout development based on targeted degradation of plant-specific transcriptional regulators, the group VII ethylene response factors (ERFs). We show that the N-end rule pathway of targeted proteolysis targets these proteins for destruction in the presence of NO, and we establish them as critical regulators of diverse NO-regulated processes, including seed germination, stomatal closure, and hypocotyl elongation. Furthermore, we define the molecular mechanism for NO control of germination and crosstalk with abscisic acid (ABA) signaling through ERF-regulated expression of ABSCISIC ACID INSENSITIVE5 (ABI5). Our work demonstrates how NO sensing is integrated across multiple physiological processes by direct modulation of transcription factor stability and identifies group VII ERFs as central hubs for the perception of gaseous signals in plants

PYL8 mediates ABA perception in the root through non-cell-autonomous and ligand-stabilization-based mechanisms

[EN] The phytohormone abscisic acid (ABA) plays a key role regulating root growth, root system architecture, and root adaptive responses, such as hydrotropism. The molecular and cellular mechanisms that regulate the action of core ABA signaling components in roots are not fully understood. ABA is perceived through receptors from the PYR/PYL/RCAR family and PP2C coreceptors. PYL8/RCAR3 plays a nonredundant role in regulating primary and lateral root growth. Here we demonstrate that ABA specifically stabilizes PYL8 compared with other ABA receptors and induces accumulation of PYL8 in root nuclei. This requires ABA perception by PYL8 and leads to diminished ubiquitination of PYL8 in roots. The ABA agonist quinabactin, which promotes root ABA signaling through dimeric receptors, fails to stabilize the monomeric receptor PYL8. Moreover, a PYL8 mutant unable to bind ABA and inhibit PP2C is not stabilized by the ligand, whereas a PYL85KR mutant is more stable than PYL8 at endogenous ABA concentrations. The PYL8 transcript was detected in the epidermis and stele of the root meristem; however, the PYL8 protein was also detected in adjacent tissues. Expression of PYL8 driven by tissue-specific promoters revealed movement to adjacent tissues. Hence both inter- and intracellular trafficking of PYL8 appears to occur in the root apical meristem. Our findings reveal a non-cell-autonomous mechanism for hormone receptors and help explain the nonredundant role of PYL8-mediated root ABA signaling.Work in the P.L.R. and F.M. laboratories was supported by the Ministerio de Ciencia e Innovacion, Fondo Europeo de Desarrollo Regional and Consejo Superior de Investigaciones Cientificas Grants BIO2014-52537-R and BIO2017-82503-R (to P.L.R.) and BIO2015-64307-R (to F.M.). J.L.-J. was supported by a Juan de la Cierva contract from Ministerio de Economia y Competitividad (MINECO) and by the Marie Sklodowska-Curie Action H2020-MSCA-IF-2015-707477. B.B.-P. was funded by Programa VALi+d GVA APOSTD/2017/039. J.J. was supported by a FPI contract from MINECO and M.A.F. by a Formacion de Profesorado Universitario contract from MINECO. D.D. and M.J.B. were supported by Biotechnology and Biological Sciences Research Council Grant BB/M002136/1 and Leverhulme Trust Grant RPG-2016-409.Belda-Palazón, B.; Gonzalez-Garcia, M.; Lozano Juste, J.; Coego Gonzalez, A.; Antoni-Alandes, R.; Julian-Valenzuela, J.; Peirats-Llobet, M.... (2018). PYL8 mediates ABA perception in the root through non-cell-autonomous and ligand-stabilization-based mechanisms. Proceedings of the National Academy of Sciences of the United States of America (Online). 115(50):E11857-E11863. https://doi.org/10.1073/pnas.1815410115SE11857E1186311550Ubeda-Tomás, S., Beemster, G. T. S., & Bennett, M. J. 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Nitric oxide responses in Arabidopsis hypocotyls are mediated by diverse phytohormone pathways

[EN] Plants are often exposed to high levels of nitric oxide (NO) that affects development and stress-triggered responses. However, the way in which plants sense NO is still largely unknown. Here we combine the analysis of early changes in the transcriptome of plants exposed to a short acute pulse of exogenous NO with the identification of transcription factors (TFs) involved in NO sensing. The NO-responsive transcriptome was enriched in hormone homeostasis and signaling-related genes. To assess events involved in NO sensing in hypocotyls, we used a functional sensing assay based on the NO-induced inhibition of hypocotyl elongation in etiolated seedlings. Hormone-related mutants and the TRANSPLANTA collection of transgenic lines conditionally expressing Arabidopsis TFs were screened for NO-triggered hypocotyl shortening. These approaches allowed the identification of hormone-related TFs, ethylene perception and signaling, strigolactone biosynthesis and signaling, and salicylate production and accumulation that are essential for or modulate hypocotyl NO sensing. Moreover, NO inhibits hypocotyl elongation through the positive and negative regulation of some abscisic acid (ABA) receptors and transcripts encoding brassinosteroid signaling components thereby also implicating these hormones in NO sensing.This work was supported by grants BIO2014-56067-P and BIO2017-82945-P from the Spanish Ministry of Economy, Industry and Competitiveness and FEDER funds. We thank the Genomics Unit of the Centro Nacional de Biotecnologia (CNB-CSIC, Madrid, Spain) for microarray processing. We gratefully acknowledged the kind donation of mutant seeds: Roberto Solano and Andrea Chini (CNB, Madrid, Spain) for the jaz and myc mutants; Paul Verslues (Institute of Plant and Microbial Biology, Academia Sinica, Taiwan) for the hai mutants; Javier Agusti, Pablo Tornero, and Pedro Rodriguez (IBMCP, Valencia, Spain) for the max, sid2eds5nahG, and pyr/pyl mutants, respectively; and Hiroaki Fujii (University of Turku, Finland) for the snrk2.3 and 2.9 mutants.Castillo López Del Toro, MC.; Coego Gonzalez, A.; Costa-Broseta, Á.; Leon Ramos, J. (2018). Nitric oxide responses in Arabidopsis hypocotyls are mediated by diverse phytohormone pathways. Journal of Experimental Botany. 69(21):5265-5278. https://doi.org/10.1093/jxb/ery286S52655278692

Diverse functional interactions between nitric oxide and abscisic acid in plant development and responses to stress

[EN] The extensive support for abscisic acid (ABA) involvement in the complex regulatory networks controlling stress responses and development in plants contrasts with the relatively recent role assigned to nitric oxide (NO). Because treatment with exogenous ABA leads to enhanced production of NO, it has been widely considered that NO participates downstream of ABA in controlling processes such as stomata movement, seed dormancy, and germination. However, data on leaf senescence and responses to stress suggest that the functional interaction between ABA and NO is more complex than previously thought, including not only cooperation but also antagonism. The functional relationship is probably determined by several factors including the time- and place-dependent pattern of accumulation of both molecules, the threshold levels, and the regulatory factors important for perception. These factors will determine the actions exerted by each regulator. Here, several examples of well-documented functional interactions between NO and ABA are analysed in light of the most recent reported data on seed dormancy and germination, stomata movements, leaf senescence, and responses to abiotic and biotic stressesThis work was supported by MICINN (Spain) grants BIO2011-27526 and CONSOLIDER CSD2007-00057 to JL and postdoctoral contracts to MCC and AC. RM was funded by a pre-doctoral fellowship of the FPU Program from MEC (Spain). We thank Michael Holdsworth (University of Nottingham, UK) for critical reading of this manuscript and for his helpful comments and corrections. We would also like to express our appreciation for all the contributions reported in this research area, and particularly to those researchers who have not been cited in this review because of the limitations of manuscript length.Leon Ramos, J.; Castillo López Del Toro, MC.; Coego González, A.; Lozano Juste, J.; Mir Moreno, R. (2014). 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