Long-distance ABA transport can mediate distal tissue responses by affecting local ABA concentrations

Environmental stresses that perturb plant water relations influence abscisic acid (ABA) concentrations, but it is unclear whether long-distance ABA transport contributes to changes in local ABA levels. To determine the physiological relevance of ABA transport, we made reciprocal- and self-grafts of ABA-deficient flacca mutant and wild-type (WT) tomato plants, in which low phosphorus (P) conditions decreased ABA concentrations while salinity increased ABA concentrations. Whereas foliar ABA concentrations in the WT scions were rootstock independent under conditions, salinity resulted in long-distance transport of ABA: flacca scions had approximately twice as much ABA when grafted on WT rootstocks compared to flacca rootstocks. Root ABA concentrations were scion dependent: both WT and flacca rootstocks had less ABA with the flacca mutant scion than with the WT scion under conditions. In WT scions, whereas rootstock genotype had limited effects on stomatal conductance under conditions, a flacca rootstock decreased leaf area of stressed plants, presumably due to attenuated root-to-shoot ABA transport. In flacca scions, a WT rootstock decreased stomatal conductance but increased leaf area of stressed plants, likely due to enhanced root-to-shoot ABA transport. Thus, long-distance ABA transport can affect responses in distal tissues by changing local ABA concentrations

La infancia robada : el trabajo infantil en la República Dominicana

"La infància robada" és un reportatge audiovisual sobre un dels problemes socials més importants de la República Dominicana: el treball infantil. Encara milers de nens es troben en situació de treball infantil per ajudar econòmicament les seves famílies. El reportatge s'endinsa en diferents històries d'infants que treballen i, alhora, experts en l'àmbit del dret laboral, dels drets humans i diversos polítics del país expliquen com és el treball infantil a la República Dominicana i quines són les mesures que tant el govern com altres institucions proposen per fer front al problema."La infancia robada" es un reportaje audiovisual sobre uno de los problemas sociales más importantes de la República Dominicana: el trabajo infantil. Aún miles de niños se encuentran en situación de trabajo infantil para ayudar económicamente a sus familias. El reportaje se adentra en diferentes historias de niños que trabajan y, al mismo tiempo, expertos en el ámbito del derecho laboral, de los derechos humanos y políticos del país explican cómo es el trabajo infantil en la República Dominicana y cuáles son las medidas que tanto el gobierno como otras instituciones proponen para hacer frente al problema."The stolen childhood" is an audiovisual report about one of the most important social problems in the Dominican Republic: child labour. Thousands of children are in a situation of child labour to help their families financially. The audiovisual delves into different stories of working children and, at the same time, experts in the field of labour law, human rights and politicians of the country explain how is child labour in the Dominican Republic and what are the measures that the government and other institutions propose to deal with the problem

Utilización del cultivo de tejidos vegetales in vitro para el estudio de la respuesta de los cítricos al estrés salino

Este trabajo describe la puesta a punto de un sistema in vitro para el estudio de la toxicidad del NaCl en tres genotipos de cítricos, evitando el filtro de iones que constituye la raíz. Los cultivos se establecieron a partir de plantas de mandarino Cleopatra, citrange Carrizo y citrumelo CPB4475 cultivadas en invernadero. Se ensayaron diferentes concentraciones de NaCl y se seleccionó 60 mM como tratamiento salino para los diferentes experimentos. Los brotes de todos los genotipos estudiados acumularon concentraciones similares de iones cloruro cuando se cultivaron desprovistos del sistema radicular y mostraron los mismos daños foliares. No se observó incremento en la concentración de malondialdehido (como indicador del daño oxidativo) en ninguno de los genotipos y todos ellos mostraron patrones similares de señalización hormonal, con independencia de su tolerancia o sensibilidad cuando se cultivan en campo. El sistema in vitro descrito se postula como una herramienta útil para el estudio de los procesos bioquímicos implicados en la respuesta de los cítricos al estrés salino.In this work, an in vitro experimental system has been developed to study the toxic effect of NaCl on three citrus genotypes, avoiding the ion filter that represents the root system. Cultures were established from greenhouse growing plants of Cleopatra mandarin, Carrizo citrange and citrumelo CPB4475. Several salt concentrations were tested and 60 mM NaCl was selected as saline treatment. Shoots from all studied genotypes accumulated similar levels of chloride when cultured without roots and exhibited similar leaf damage. No increases in malondialdehyde levels (as a measure of oxidative stress) were observed in any genotype and similar patterns of hormonal signalling were exhibited in the three genotypes, despite their different tolerance under field conditions. The in vitro culture system has been proved as a useful tool to study biochemical processes involved in the response of citrus to salt stress.Este estudio fue financiado por el Ministerio de Ciencia e Innovación y la Fundació Bancaixa/Universitat Jaume I a través de la concesión de los proyectos AGL2010-22195-C03-01/AGR y P1 1B2009-01, respectivament

Soil moisture heterogeneity regulates water use in Populus nigra L. by altering root and xylem sap phytohormone concentrations

Soil moisture heterogeneity in the root-zone is common during both the establishment of tree seedlings and in experiments aiming to impose semi-constant soil moisture deficits, but its effects on regulating plant water use compared to homogenous soil drying are not well known in trees. Pronounced vertical soil moisture heterogeneity was imposed on black poplar (Populus nigra L.) grown in soil columns by altering irrigation frequency, to test whether plant water use, hydraulic responses, root phytohormone concentrations, and root xylem sap chemical composition differed between wet (well-watered, WW), homogeneously (infrequent deficit irrigation, IDI) and heterogeneously dry soil (frequent deficit irrigation, FDI). At the same bulk soil water content, FDI plants had greater water use than IDI plants, probably because root abscisic acid (ABA) concentration was low in the upper wetter layer of FDI plants, which maintained root xylem sap ABA concentration at basal levels in contrast with IDI. Soil drying did not increase root xylem concentration of any other hormone. Nevertheless, plant-to-plant variation in xylem jasmonic acid (JA) concentration was negatively related to leaf stomatal conductance within WW and FDI plants. However, feeding detached leaves with high (1,200 nM) JA concentrations via the transpiration stream decreased transpiration only marginally. Xylem pH and sulphate concentration decreased in FDI plants compared to well-watered plants. Frequent deficit irrigation increased root accumulation of the cytokinin trans-zeatin (tZ), especially in the dry lower layer, and of the ethylene precursor ACC, in the wet upper soil layer. Root hormone accumulation might explain the maintenance of high root hydraulic conductance and water use in FDI plants (similar to well-watered plants) compared to IDI plants. In irrigated tree crops, growers could vary irrigation scheduling to control water use by altering the hormone balance

Identification of ABA-Mediated Genetic and Metabolic Responses to Soil Flooding in Tomato (Solanum lycopersicum L. Mill)

[EN] Soil flooding is a compound abiotic stress that alters soil properties and limits atmospheric gas diffusion (O-2 and CO2) to the roots. The involvement of abscisic acid (ABA) in the regulation of soil flooding-specific genetic and metabolic responses has been scarcely studied despite its key importance as regulator in other abiotic stress conditions. To attain this objective, wild type and ABA-deficient tomatoes were subjected to short-term (24 h) soil waterlogging. After this period, gas exchange parameters were reduced in the wild type but not in ABA-deficient plants that always had higher E and g(s). Transcript and metabolite alterations were more intense in waterlogged tissues, with genotype-specific variations. Waterlogging reduced the ABA levels in the roots while inducing PYR/PYL/RCAR ABA receptors and ABA-dependent transcription factor transcripts, of which induction was less pronounced in the ABA-deficient genotype. Ethylene/O-2-dependent genetic responses (ERFVIIs, plant anoxia survival responses, and genes involved in the N-degron pathway) were induced in hypoxic tissues independently of the genotype. Interestingly, genes encoding a nitrate reductase and a phytoglobin involved in NO biosynthesis and scavenging and ERFVII stability were induced in waterlogged tissues, but to a lower extent in ABA-deficient tomato. At the metabolic level, flooding-induced accumulation of Ala was enhanced in ABA-deficient lines following a differential accumulation of Glu and Asp in both hypoxic and aerated tissues, supporting their involvement as sources of oxalacetate to feed the tricarboxylic acid cycle in waterlogged tissues and constituting a potential advantage upon long periods of soil waterlogging. The promoter analysis of upregulated genes indicated that the production of oxalacetate from Asp via Asp oxidase, energy processes such as acetyl-CoA, ATP, and starch biosynthesis, and the lignification process were likely subjected to ABA regulation. Taken together, these data indicate that ABA depletion in waterlogged tissues acts as a positive signal, inducing several specific genetic and metabolic responses to soil flooding.This work was supported by the Spanish Ministerio de Economia y Competitividad, Universitat Jaume I and Generalitat Valenciana/Fondo Europeo de Desarrollo Regional (FEDER), co-funded through grant nos. AGL2016-76574-R, UJI-B201623, UJI-B2016-24, IDIFEDER/2018/010, and UJI-B2019-24 to AG-C, VA, and MG-G, respectively. CD was supported by UJI PICD program. MG-G and JM were supported by Ramon y Cajal contracts from Spanish Ministerio de Economia y Competitividad (RYC-2016-19325 and RYC-201723645, respectively). JR was supported by a Juan de la CiervaFormacion contract from the Spanish Ministerio de Economia y Competitividad (FJCI-2016-28601).De Ollas, C.; González-Guzmán, M.; Pitarch, Z.; Matus, JT.; Candela, H.; Rambla Nebot, JL.; Granell Richart, A.... (2021). Identification of ABA-Mediated Genetic and Metabolic Responses to Soil Flooding in Tomato (Solanum lycopersicum L. Mill). Frontiers in Plant Science. 12:1-20. https://doi.org/10.3389/fpls.2021.613059S1201

Terpene down-regulation triggers defense responses in transgenic oranges leading to resistance against fungal pathogens

Terpenoid volatiles are isoprene compounds that are emitted by plants to communicate with the environment. In addition to their function in repelling herbivores and attracting carnivorous predators in green tissues, the presumed primary function of terpenoid volatiles released from mature fruits is the attraction of seed-dispersing animals. Mature oranges (Citrus sinensis) primarily accumulate terpenes in peel oil glands, with D-limonene accounting for approximately 97% of the total volatile terpenes. In a previous report, we showed that down-regulation of a D-limonene synthase gene alters monoterpene levels in orange antisense (AS) fruits, leading to resistance against Penicillium digitatum infection. A global gene expression analysis of AS versus empty vector (EV) transgenic fruits revealed that the down-regulation of D-limonene up-regulated genes involved in the innate immune response. Basal levels of jasmonic acid were substantially higher in the EV compared with AS oranges. Upon fungal challenge, salicylic acid levels were triggered in EV samples, while jasmonic acid metabolism and signaling were drastically increased in AS orange peels. In nature, D-limonene levels increase in orange fruit once the seeds are fully viable. The inverse correlation between the increase in D-limonene content and the decrease in the defense response suggests that D-limonene promotes infection by microorganisms that are likely involved in facilitating access to the pulp for seed-dispersing frugivores.This work was supported by the Fondo Europeo de Desarrollo Regional and the Ministry of Science and Innovation of Spain (grant no. AGL2009-08052), by the Fundo de Defesa da Citricultura, and by the Instituto Valenciano de Investigaciones Agrarias, Spain (Ph.D. fellowship to A.R.).Rodríguez, A.; Shimada, T.; Cervera, M.; Alquézar, B.; Gadea Vacas, J.; Gómez-Cadenas, A.; De Ollas, CJ.... (2014). Terpene down-regulation triggers defense responses in transgenic oranges leading to resistance against fungal pathogens. Plant Physiology. 164(1):321-339. https://doi.org/10.1104/pp.113.224279S321339164

Jasmonoyl isoleucine accumulation is needed for abscisic acid build-up in roots of Arabidopsis under water stress conditions

Phytohormones are central players in sensing and signallingnumerous environmental conditions like drought. In thiswork, hormone profiling together with gene expression ofkey enzymes involved in abscisic acid (ABA) and jasmonatebiosynthesis were studied in desiccating Arabidopsis roots.Jasmonic acid (JA) content transiently increased after stressimposition whereas progressive and concomitant ABA andJasmonoyl Isoleucine (JA-Ile) accumulations were detected.Molecular data suggest that, at least, part of the hormonalregulation takes place at the biosynthetic level. These obser-vations also point to a possible involvement of jasmonates onABA biosynthesis under stress. To test this hypothesis,mutants impaired in jasmonate biosynthesis (opr3, lox6 andjar1-1) and in JA-dependent signalling (coi1) wereemployed. Results showed that the early JA accumulationleading to JA-Ile build up was necessary for an ABA increasein roots under two different water stress conditions. Signaltransduction between water stress-induced JA-Ile accumula-tion and COI1 is necessary for a full induction of the ABAbiosynthesis pathway and subsequent hormone accumula-tion in roots of Arabidopsis plants. The present work adds alevel of interaction between jasmonates and ABA at thebiosynthetic levelThis work was supported by the Spanish Ministerio deEconomía y Competitividad (MINECO) through grantsAGL2010-22195-C03-01 and AGL2013-42038R to A.G.-C.Hormonal profiles were performed at Instrumental centralfacilities (SCIC) of Universitat Jaume I. The authors have noconflict of interest to declar

Depletion of abscisic acid levels in roots of flooded Carrizo citrange (Poncirus trifoliata L. Raf. x Citrus sinensis L. Osb.) plants is a stress-specific response associated to the differential expression of PYR/PYL/RCAR receptors

[EN] Soil flooding reduces root abscisic acid (ABA) levels in citrus, conversely to what happens under drought. Despite this reduction, microarray analyses suggested the existence of a residual ABA signaling in roots of flooded Carrizo citrange seedlings. The comparison of ABA metabolism and signaling in roots of flooded and water stressed plants of Carrizo citrange revealed that the hormone depletion was linked to the upregulation of CsAOG, involved in ABA glycosyl ester (ABAGE) synthesis, and to a moderate induction of catabolism (CsCYP707A, an ABA 8'-hydroxylase) and buildup of dehydrophaseic acid (DPA). Drought strongly induced both ABA biosynthesis and catabolism (CsNCED1, 9-cis-neoxanthin epoxycarotenoid dioxygenase 1, and CsCYP707A) rendering a significant hormone accumulation. In roots of flooded plants, restoration of control ABA levels after stress release was associated to the upregulation of CsBGLU18 (an ABA beta-glycosidase) that cleaves ABAGE. Transcriptional profile of ABA receptor genes revealed a different induction in response to soil flooding (CsPYL5) or drought (CsPYL8). These two receptor genes along with CsPYL1 were cloned and expressed in a heterologous system. Recombinant CsPYL5 inhibited Delta NHAB1 activity in vitro at lower ABA concentrations than CsPYL8 or CsPYL1, suggesting its better performance under soil flooding conditions. Both stress conditions induced ABA-responsive genes CsABI5 and CsDREB2A similarly, suggesting the occurrence of ABA signaling in roots of flooded citrus seedlings. The impact of reduced ABA levels in flooded roots on CsPYL5 expression along with its higher hormone affinity reinforce the role of this ABA receptor under soil-flooding conditions and explain the expression of certain ABA-responsive genes.This work was supported by Ministerio de Economia y Competitividad (MINECO), Fondo Europeo de Desarrollo Regional (FEDER) and Universitat Jaume I through grants No. AGL201676574-R, UJI-B2016-23/UJI-B2016-24 to A.G-C. and V.A. and MINECO, FEDER and Consejo Superior de Investigaciones Cientificas (CSIC) through grant BIO2014-52537-R to P.L.R. S.I.Z. and M.M. were supported by predoctoral grants from Universitat Jaume I and Generalitat Valenciana, respectively. M.G.G. was recipient of a "JAE-DOC" contract from the CSIC. Mass spectrometry analyses were performed at the central facilities (Servei Central d'Instrumentacio Cientifica, SCIC) of Universitat Jaume I.Arbona, V.; Zandalinas, SI.; Manzi, M.; González Guzmán, M.; Rodríguez Egea, PL.; Gómez-Cadenas, A. (2017). Depletion of abscisic acid levels in roots of flooded Carrizo citrange (Poncirus trifoliata L. Raf. x Citrus sinensis L. Osb.) plants is a stress-specific response associated to the differential expression of PYR/PYL/RCAR receptors. Plant Molecular Biology. 93(6):623-640. https://doi.org/10.1007/s11103-017-0587-7S623640936Agarwal PK, Jha B (2010) Transcription factors in plants and ABA dependent and independent abiotic stress signalling. Biol Plant 54:201–212Agustí J, Merelo P, Cercós M, Tadeo FR, Talón M (2008) Ethylene-induced differential gene expression during abscission of citrus leaves. J Exp Bot 59:2717–2733. doi: 10.1093/jxb/ern138Antoni R, Gonzalez-Guzman M, Rodriguez L, Rodrigues A, Pizzio G, Rodriguez PL (2012) Selective inhibition of clade a phosphatases type 2 C by PYR/PYL/RCAR abscisic acid receptors. Plant Physiol 158:970–980. doi: 10.1104/pp.111.188623Antoni R, Gonzalez-Guzman M, Rodriguez L, Peirats-Llobet M, Pizzio G, Fernandez M, De Winne N, De Jaeger G, Dietrich D, Bennett MJ, Rodriguez PL (2013) PYRABACTIN RESISTANCE1-LIKE8 plays an important role for the regulation of abscisic acid signaling in root. Plant Physiol 161:491–931. doi: 10.1104/pp.112.208678Arbona V, Gómez-Cadenas A (2008) Hormonal modulation of citrus responses to flooding. J Plant Growth Regul 27:241–250. doi: 10.1007/s00344-008-9051-xArbona V, López-climent MF, Pérez-Clemente RM, Gómez-cadenas A (2009) Maintenance of a high photosynthetic performance is linked to flooding tolerance in citrus. Environ Exp Bot 66:135–142. doi: 10.1016/j.envexpbot.2008.12.011Argamasilla R, Gómez-Cadenas A, Arbona V (2013) Metabolic and regulatory responses in citrus rootstocks in response to adverse environmental conditions. J Plant Growth Regul 33:169–180. doi: 10.1007/s00344-013-9359-zBaron KN, Schroeder DF, Stasolla C (2012) Transcriptional response of abscisic acid (ABA) metabolism and transport to cold and heat stress applied at the reproductive stage of development in Arabidopsis thaliana. Plant Sci 188–189:48–59. doi: 10.1016/j.plantsci.2012.03.001Benschop JJ, Millenaar FF, Smeets ME, Van Zanten M, Voesenek LACJ, Peeters AJM (2007) Abscisic acid antagonizes ethylene-induced hyponastic growth in Arabidopsis. Plant Physiol 143:1013–1023Chen R, Jiang H, Li L, Zhai Q, Qi L, Zhou W, Liu X, Li H, Zheng W, Sun J, Li C (2012) The Arabidopsis mediator subunit MED25 differentially regulates jasmonate and abscisic acid signaling through interacting with the MYC2 and ABI5 transcription factors. Plant Cell 24:2898–2916. doi: 10.1105/tpc.112.098277De Ollas C, Hernando B, Arbona V, Gómez-Cadenas A (2013) Jasmonic acid transient accumulation is needed for abscisic acid increase in citrus roots under drought stress conditions. Physiol Plant 147:296–306. doi: 10.1111/j.1399-3054.2012.01659.xDupeux F, Santiago J, Betz K, Twycross J, Park S-Y, Rodriguez L, Gonzalez-Guzman M, Jensen MR, Krasnogor N, Blackledge M, Holdsworth M, Cutler SR, Rodriguez PL, Márquez JA (2011) A thermodynamic switch modulates abscisic acid receptor sensitivity. EMBO J 30:4171–4184. doi: 10.1038/emboj.2011.294Finkelstein RR, Rock CD (2002) Abscisic Acid biosynthesis and response. Arabidopsis Book 1:e0058. doi: 10.1199/tab.0058Fuchs S, Tischer SV, Wunschel C, Christmann A, Grill E (2014) Abscisic acid sensor RCAR7/PYL13, specific regulator of protein phosphatase coreceptors. Proc Natl Acad Sci U S A 111:5741–5746. doi: 10.1073/pnas.1322085111Fukao T, Yeung E, Bailey-Serres J (2011) The submergence tolerance regulator SUB1A mediates crosstalk between submergence and drought tolerance in rice. Plant Cell 23:412–427. doi: 10.1105/tpc.110.080325Gonzalez-Guzman M, Rodriguez L, Lorenzo-Orts L, Pons C, Sarrion-Perdigones A, Fernandez M a, Peirats-Llobet M, Forment J, Moreno-Alvero M, Cutler SR, Albert A, Granell A, Rodriguez PL (2014) Tomato PYR/PYL/RCAR abscisic acid receptors show high expression in root, differential sensitivity to the abscisic acid agonist quinabactin, and the capability to enhance plant drought resistance. J Exp Bot 65:1–14. doi: 10.1093/jxb/eru219González-Guzmán M, Apostolova N, Bellés JM, Barrero JM, Piqueras P, Ponce MR, Micol JL, Serrano R, Rodríguez PL (2002) The short-chain alcohol dehydrogenase ABA2 catalyzes the conversion of xanthoxin to abscisic aldehyde. Plant Cell 14:1833–1846. doi: 10.1105/tpc.002477.developmentHsu F-C, Chou M-Y, Peng H-P, Chou S-J, Shih M-C (2011) Insights into hypoxic systemic responses based on analyses of transcriptional regulation in Arabidopsis. PLoS ONE 6:e28888. doi: 10.1371/journal.pone.0028888Krochko JE, Abrams GD, Loewen MK, Abrams SR, Cutler AJ (1998) (+)-Abscisic Acid 8-hydroxylase is a cytochrome P450 monooxygenase. Plant Physiol 860:849–860. doi: 10.1104/pp.118.3.849Lawlor DW (2013) Genetic engineering to improve plant performance under drought: physiological evaluation of achievements, limitations, and possibilities. J Exp Bot 64:83–108. doi: 10.1093/jxb/ers326Lee SC, Luan S (2012) ABA signal transduction at the crossroad of biotic and abiotic stress responses. Plant Cell Environ 35:53–60. doi: 10.1111/j.1365-3040.2011.02426.xLiu Q, Kasuga M, Sakuma Y, Abe H, Miura S, Yamaguchi-Shinozaki K, Shinozaki K (1998) Two transcription factors, DREB1 and DREB2, with an EREBP/AP2 DNA binding domain separate two cellular signal transduction pathways in drought- and low-temperature-responsive gene expression, respectively, in Arabidopsis. Plant Cell 10:1391–1406Mittal A, Gampala SSL, Ritchie GL, Payton P, Burke JJ, Rock CD (2014) Related to ABA-Insensitive3(ABI3)/Viviparous1 and AtABI5 transcription factor coexpression in cotton enhances drought stress adaptation. Plant Biotechnol J 12:578–589. doi: 10.1111/pbi.12162Naika M, Shameer K, Mathew OK, Gowda R, Sowdhamini R (2013) STIFDB2: an updated version of plant stress-responsive transcription factor database with additional stress signals, stress-responsive transcription factor binding sites and stress-responsive genes in Arabidopsis and rice. Plant Cell Physiol 54:e8. doi: 10.1093/pcp/pcs185Nambara E, Marion-Poll A (2005) Abscisic acid biosynthesis and catabolism. Annu Rev Plant Biol 56:165–185. doi: 10.1146/annurev.arplant.56.032604.144046Narusaka Y, Nakashima K, Shinwari ZK, Sakuma Y, Furihata T, Abe H, Narusaka M, Shinozaki K, Yamaguchi-Shinozaki K (2003) Interaction between two cis-acting elements, ABRE and DRE, in ABA-dependent expression of Arabidopsis rd29A gene in response to dehydration and high-salinity stresses. Plant J 34:137–148Okamoto M, Kuwahara A, Seo M, Kushiro T, Asami T, Hirai N (2006) CYP707A1 and CYP707A2, which encode abscisic acid 8′-hydroxylases, are indispensable for proper control of seed dormancy and germination in Arabidopsis. Plant Physiol 141:97–107. doi: 10.1104/pp.106.079475.1Okamoto M, Peterson FC, Defries A, Park S-Y, Endo A, Nambara E, Volkman BF, Cutler SR (2013) Activation of dimeric ABA receptors elicits guard cell closure, ABA-regulated gene expression, and drought tolerance. Proc Natl Acad Sci USA 110:12132–12137. doi: 10.1073/pnas.1305919110Priest DM, Ambrose SJ, Vaistij FE, Elias L, Higgins GS, Ross ARS, Abrams SR, Bowles DJ (2006) Use of the glucosyltransferase UGT71B6 to disturb abscisic acid homeostasis in Arabidopsis thaliana. Plant J 46:492–502. doi: 10.1111/j.1365-313X.2006.02701.xRitchie M, Phipson B, Wu D, Hu Y, Law C, Shi W, Smyth G (2015) Limma powers differential expression analyses for RNA-sequencing and microarray studies. Nucleic Acids Res 43:e47Rodríguez-Gamir J, Ancillo G, González-Mas MC, Primo-Millo E, Iglesias DJ, Forner-Giner MA (2011) Root signalling and modulation of stomatal closure in flooded citrus seedlings. Plant Physiol Biochem 49:636–645. doi: 10.1016/j.plaphy.2011.03.003Romero P, Lafuente MT, Rodrigo MJ (2012a) The Citrus ABA signalosome: identification and transcriptional regulation during sweet orange fruit ripening and leaf dehydration. J Exp Bot 63:4931–4945Romero P, Rodrigo MJ, Alférez F, Ballester A-R, González-Candelas L, Zacarías L, Lafuente MT (2012b) Unravelling molecular responses to moderate dehydration in harvested fruit of sweet orange (Citrus sinensis L. Osbeck) using a fruit-specific ABA-deficient mutant. J Exp Bot 63:2753–2767. doi: 10.1093/jxb/err461Saika H, Okamoto M, Miyoshi K, Kushiro T, Shinoda S, Jikumaru Y, Fujimoto M, Arikawa T, Takahashi H, Ando M, Arimura S-I, Miyao A, Hirochika H, Kamiya Y, Tsutsumi N, Nambara E, Nakazono M (2007) Ethylene promotes submergence-induced expression of OsABA8ox1, a gene that encodes ABA 8′-hydroxylase in rice. Plant Cell Physiol 48:287–298. doi: 10.1093/pcp/pcm003Santiago J, Dupeux F, Betz K, Antoni R, Gonzalez-Guzman M, Rodriguez L, Márquez JA, Rodriguez PL (2012) Structural insights into PYR/PYL/RCAR ABA receptors and PP2Cs. Plant Sci 182:3–11. doi: 10.1016/j.plantsci.2010.11.014Schroeder JI, Nambara E (2006) A quick release mechanism for abscisic acid. Cell 126:1023–1025. doi: 10.1016/j.cell.2006.09.001Seiler C, Harshavardhan VT, Rajesh K, Reddy PS, Strickert M, Rolletschek H, Scholz U, Wobus U, Sreenivasulu N (2011) ABA biosynthesis and degradation contributing to ABA homeostasis during barley seed development under control and terminal drought-stress conditions. J Exp Bot 62:2615–2632. doi: 10.1093/jxb/erq446Shimamura S, Yoshioka T, Yamamoto R, Hiraga S, Nakamura T, Shimada S, Komatsu S (2014) Role of abscisic acid in flood-induced secondary aerenchyma formation in soybean (Glycine max) hypocotyls. Plant Prod Sci 17:131–137. doi: 10.1626/pps.17.131Szostkiewicz I, Richter K, Kepka M, Demmel S, Ma Y, Korte A, Assaad FF, Christmann A, Grill E (2010) Closely related receptor complexes differ in their ABA selectivity and sensitivity. Plant J 61:25–35. doi: 10.1111/j.1365-313X.2009.04025.xTanaka H, Osakabe Y, Katsura S, Mizuno S, Maruyama K, Kusakabe K, Mizoi J, Shinozaki K, Yamaguchi-Shinozaki K (2012) Abiotic stress-inducible receptor-like kinases negatively control ABA signaling in Arabidopsis. Plant J 70:599–613. doi: 10.1111/j.1365-313X.2012.04901.xValdés AE, Övernäs E, Johansson H, Rada-Iglesias A, Engström P (2012) The homeodomain-leucine zipper (HD-Zip) class I transcription factors ATHB7 and ATHB12 modulate abscisic acid signalling by regulating protein phosphatase 2C and abscisic acid receptor gene activities. Plant Mol Biol 80:405–418. doi: 10.1007/s11103-012-9956-4Weng J-K, Ye M, Noel JP (2016) Co-evolution of hormone metabolism and signaling networks expands plant adaptive plasticity. Cell 166:881–893Yamaguchi M, Sharp RE (2010) Complexity and coordination of root growth at low water potentials: recent advances from transcriptomic and proteomic analyses. Plant Cell Environ 33:590–603. doi: 10.1111/j.1365-3040.2009.02064.xYoshida T, Mogami J, Yamaguchi-Shinozaki K (2014) ABA-dependent and ABA-independent signaling in response to osmotic stress in plants. Curr Opin Plant Biol 21C:133–139. doi: 10.1016/j.pbi.2014.07.009Zhao Y, Xing L, Wang X, Hou Y-H, Gao J, Wang P, Duan C-G, Zhu X, Zhu J-K (2014) The ABA receptor PYL8 promotes lateral root growth by enhancing MYB77-dependent transcription of auxin-responsive genes. Sci Signal 7:ra53Zou M, Guan Y, Ren H, Zhang F, Chen F (2008) A bZIP transcription factor, OsABI5, is involved in rice fertility and stress tolerance. Plant Mol Biol 66:675–683. doi: 10.1007/s11103-008-9298-

Plant size directly correlates with water use efficiency in Arabidopsis

Plant transpiration is a fundamental process that determines plant water use efficiency (WUE), thermoregulation, nutrition, and growth. How transpiration impacts on such essential physiological aspects and how the environment modulates these effects are fundamental questions about which little is known. We investigated the genetic and environmental factors underlying natural variation in plant transpiration and water use efficiency in a population of natural Arabidopsis thaliana accessions grown under homogeneous conditions. As expected, we observed large variation of total transpiration capacity, transpiration per surface unit, and WUE among A. thaliana accessions. Despite the variation of stomatal density and ABA content in the population, WUE did not correlate with any of these parameters. On the contrary, a surprising direct correlation was found between WUE and projected leaf area, with bigger plants displaying a more efficient use of water. Importantly, genome-wide association studies further supported our observations through the identification of several loci involved in WUE variation, mutations in which caused a simultaneous reduction in plant size and a decrease in WUE. Altogether, our results strongly suggest that, although WUE depends on many parameters, plant size is an adaptive trait with respect to water use in A. thaliana

Physiological impacts of ABA–JA interactions under water-limitation

Plant responses to drought stress depend on highly regulated signal transduction pathways with multiple interactions. This complex crosstalk can lead to a physiological outcome of drought avoidance or tolerance/resistance. ABA is the principal mediator of these responses due to the regulation of stomatal closure that determines plant growth and survival, but also other strategies of drought resistance such as osmotic adjustment. However, other hormones such as JA seem responsible for regulating a subset of plant responses to drought by regulating ABA biosynthesis and accumulation and ABA-dependent signalling, but also by ABA independent pathways. Here, we review recent reports of ABA–JA hormonal and molecular interactions within a physiological framework of drought tolerance. Understanding the physiological significance of this complex regulation offers opportunities to find strategies of drought tolerance that avoid unwanted side effects that limit growth and yield, and may allow biotechnological crop improvement