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1.
Phytoglobins in the nuclei, cytoplasm and chloroplasts modulate nitric oxide signaling and interact with abscisic acid.
Rubio, MC, Calvo-Begueria, L, Díaz-Mendoza, M, Elhiti, M, Moore, M, Matamoros, MA, James, EK, Díaz, I, Pérez-Rontomé, C, Villar, I, et al
The Plant journal : for cell and molecular biology. 2019;(1):38-54
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Abstract
Symbiotic hemoglobins provide O2 to N2 -fixing bacteria within legume nodules, but the functions of non-symbiotic hemoglobins or phytoglobins (Glbs) are much less defined. Immunolabeling combined with confocal microscopy of the Glbs tagged at the C-terminus with green fluorescent protein was used to determine their subcellular localizations in Arabidopsis and Lotus japonicus. Recombinant proteins were used to examine nitric oxide (NO) scavenging in vitro and transgenic plants to show S-nitrosylation and other in vivo interactions with NO and abscisic acid (ABA) responses. We found that Glbs occur in the nuclei, chloroplasts and amyloplasts of both model plants, and also in the cytoplasm of Arabidopsis cells. The proteins show similar NO dioxygenase activities in vitro, are nitrosylated in Cys residues in vivo, and scavenge NO in the stomatal cells. The Cys/Ser mutation does not affect NO dioxygenase activity, and S-nitrosylation does not significantly consume NO. We demonstrate an interaction between Glbs and ABA on several grounds: Glb1 and Glb2 scavenge NO produced in stomatal guard cells following ABA supply; plants overexpressing Glb1 show higher constitutive expression of the ABA responsive genes Responsive to ABA (RAB18), Responsive to Dehydration (RD29A) and Highly ABA-Induced 2 (HAI2), and are more tolerant to dehydration; and ABA strongly upregulates class 1 Glbs. We conclude that Glbs modulate NO and interact with ABA in crucial physiological processes such as the plant's response to dessication.
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2.
Abiotic Stresses Intervene with ABA Signaling to Induce Destructive Metabolic Pathways Leading to Death: Premature Leaf Senescence in Plants.
Asad, MAU, Zakari, SA, Zhao, Q, Zhou, L, Ye, Y, Cheng, F
International journal of molecular sciences. 2019;(2)
Abstract
Abiotic stresses trigger premature leaf senescence by affecting some endogenous factors, which is an important limitation for plant growth and grain yield. Among these endogenous factors that regulate leaf senescence, abscisic acid (ABA) works as a link between the oxidase damage of cellular structure and signal molecules responding to abiotic stress during leaf senescence. Considering the importance of ABA, we collect the latest findings related to ABA biosynthesis, ABA signaling, and its inhibitory effect on chloroplast structure destruction, chlorophyll (Chl) degradation, and photosynthesis reduction. Post-translational changes in leaf senescence end with the exhaustion of nutrients, yellowing of leaves, and death of senescent tissues. In this article, we review the literature on the ABA-inducing leaf senescence mechanism in rice and Arabidopsis starting from ABA synthesis, transport, signaling receptors, and catabolism. We also predict the future outcomes of investigations related to other plants. Before changes in translation occur, ABA signaling that mediates the expression of NYC, bZIP, and WRKY transcription factors (TFs) has been investigated to explain the inducing effect on senescence-associated genes. Various factors related to calcium signaling, reactive oxygen species (ROS) production, and protein degradation are elaborated, and research gaps and potential prospects are presented. Examples of gene mutation conferring the delay or induction of leaf senescence are also described, and they may be helpful in understanding the inhibitory effect of abiotic stresses and effective measures to tolerate, minimize, or resist their inducing effect on leaf senescence.
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The biochemistry underpinning industrial seed technology and mechanical processing of sugar beet.
Ignatz, M, Hourston, JE, Turečková, V, Strnad, M, Meinhard, J, Fischer, U, Steinbrecher, T, Leubner-Metzger, G
Planta. 2019;(5):1717-1729
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Abstract
Seed-processing technologies such as polishing and washing enhance crop seed quality by limited removal of the outer layers and by leaching. Combined, this removes chemical compounds that inhibit germination. Industrial processing to deliver high-quality commercial seed includes removing chemical inhibitors of germination, and is essential to produce fresh sprouts, achieve vigorous crop establishment, and high yield potential in the field. Sugar beet (Beta vulgaris subsp. vulgaris var. altissima Doell.), the main sugar source of the temperate agricultural zone, routinely undergoes several processing steps during seed production to improve germination performance and seedling growth. Germination assays and seedling phenotyping was carried out on unprocessed, and processed (polished and washed) sugar beet fruits. Pericarp-derived solutes, known to inhibit germination, were tested in germination assays and their osmolality and conductivity assessed (ions). Abscisic acid (ABA) and ABA metabolites were quantified in both the true seed and pericarp tissue using UPLC-ESI(+)-MS/MS. Physical changes in the pericarp structures were assessed using scanning electron microscopy (SEM). We found that polishing and washing of the sugar beet fruits both had a positive effect on germination performance and seedling phenotype, and when combined, this positive effect was stronger. The mechanical action of polishing removed the outer pericarp (fruit coat) tissue (parenchyma), leaving the inner tissue (sclerenchyma) unaltered, as revealed by SEM. Polishing as well as washing removed germination inhibitors from the pericarp, specifically, ABA, ABA metabolites, and ions. Understanding the biochemistry underpinning the effectiveness of these processing treatments is key to driving further innovations in commercial seed quality.
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Nitric oxide molecular targets: reprogramming plant development upon stress.
Sánchez-Vicente, I, Fernández-Espinosa, MG, Lorenzo, O
Journal of experimental botany. 2019;(17):4441-4460
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Abstract
Plants are sessile organisms that need to complete their life cycle by the integration of different abiotic and biotic environmental signals, tailoring developmental cues and defense concomitantly. Commonly, stress responses are detrimental to plant growth and, despite the fact that intensive efforts have been made to understand both plant development and defense separately, most of the molecular basis of this trade-off remains elusive. To cope with such a diverse range of processes, plants have developed several strategies including the precise balance of key plant growth and stress regulators [i.e. phytohormones, reactive nitrogen species (RNS), and reactive oxygen species (ROS)]. Among RNS, nitric oxide (NO) is a ubiquitous gasotransmitter involved in redox homeostasis that regulates specific checkpoints to control the switch between development and stress, mainly by post-translational protein modifications comprising S-nitrosation of cysteine residues and metals, and nitration of tyrosine residues. In this review, we have sought to compile those known NO molecular targets able to balance the crossroads between plant development and stress, with special emphasis on the metabolism, perception, and signaling of the phytohormones abscisic acid and salicylic acid during abiotic and biotic stress responses.
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Abscisic acid-mediated modifications of radial apoplastic transport pathway play a key role in cadmium uptake in hyperaccumulator Sedum alfredii.
Tao, Q, Jupa, R, Liu, Y, Luo, J, Li, J, Kováč, J, Li, B, Li, Q, Wu, K, Liang, Y, et al
Plant, cell & environment. 2019;(5):1425-1440
Abstract
Abscisic acid (ABA) is a key phytohormone underlying plant resistance to toxic metals. However, regulatory effects of ABA on apoplastic transport in roots and consequences for uptake of metal ions are poorly understood. Here, we demonstrate how ABA regulates development of apoplastic barriers in roots of two ecotypes of Sedum alfredii and assess effects on cadmium (Cd) uptake. Under Cd treatment, increased endogenous ABA level was detected in roots of nonhyperaccumulating ecotype (NHE) due to up-regulated expressions of ABA biosynthesis genes (SaABA2, SaNCED), but no change was observed in hyperaccumulating ecotype (HE). Simultaneously, endodermal Casparian strips (CSs) and suberin lamellae (SL) were deposited closer to root tips of NHE compared with HE. Interestingly, the vessel-to-CSs overlap was identified as an ABA-driven anatomical trait. Results of correlation analyses and exogenous applications of ABA/Abamine indicate that ABA regulates development of both types of apoplastic barriers through promoting activities of phenylalanine ammonialyase, peroxidase, and expressions of suberin-related genes (SaCYP86A1, SaGPAT5, and SaKCS20). Using scanning ion-selected electrode technique and PTS tracer confirmed that ABA-promoted deposition of CSs and SL significantly reduced Cd entrance into root stele. Therefore, maintenance of low ABA levels in HE minimized deposition of apoplastic barriers and allowed maximization of Cd uptake via apoplastic pathway.
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Tissue Distribution and Specific Contribution of Arabidopsis FAD7 and FAD8 Plastid Desaturases to the JA- and ABA-Mediated Cold Stress or Defense Responses.
Soria-Garcï A, ÏN, Rubio, MAC, Lagunas, B, Lï Pez-Gomollï N, S, Lujï N, MALÏN, Dï Az-Guerra, RL, Picorel, R, Alfonso, M
Plant & cell physiology. 2019;(5):1025-1040
Abstract
To overcome the difficulties to analyze membrane desaturases at the protein level, transgenic Arabidopsis plants expressing the plastidial AtFAD7 and AtFAD8 ω-3 desaturases fused to green fluorescent protein, under the control of their endogenous promoters, were generated and their tissue relative abundance was studied. Gene expression, glucuronidase promoter activity, immunoblot and confocal microscopy analyses indicated that AtFAD7 is the major ω-3 desaturase in leaves when compared to AtFAD8. This higher abundance of AtFAD7 was consistent with its higher promoter activity and could be related with its specificity for the abundant leaf galactolipids. AtFAD7 was also present in roots but at much lower level than leaves. AtFAD8 expression and protein abundance in leaves was consistent with its lower promoter activity, suggesting that transcriptional control modulates the abundance of both desaturases in leaves. AtFAD7 protein levels increased in response to wounding but not to jasmonate (JA), and decreased upon abscisic acid (ABA) treatment. Conversely, AtFAD8 protein levels increased upon cold or JA exposure and decreased at high temperatures, but did not respond to ABA or wounding. These results indicated specific and non-redundant roles for the plastidial ω-3 desaturases in defense, temperature stress or phytohormone mediated responses and a tight coordination of their activities between biotic and abiotic stress signaling pathways. Our data suggested that transcriptional regulation was crucial for this coordination. Finally, bimolecular fluorescence complementation analysis showed that both AtFAD7 and AtFAD8 interact with the AtFAD6 ω-6 desaturase in vivo, suggesting that quaternary complexes are involved in trienoic fatty acid production within the plastid membranes.
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ABA Transport and Plant Water Stress Responses.
Kuromori, T, Seo, M, Shinozaki, K
Trends in plant science. 2018;(6):513-522
Abstract
To understand the integrative networks of signaling molecules, the sites of their biosynthesis and action must be clarified, particularly for phytohormones such as abscisic acid (ABA). The relationship between the sites of ABA biosynthesis and transport has been discussed extensively in the context of guard cells and stomatal regulation. However, guard cells are not the only site of ABA action. Recent studies have reported multiple sites of ABA biosynthesis and multiple ABA transporters, indicating that ABA transport regulation is not unidirectional but rather forms complex networks. Therefore, it is important to determine how multiple ABA sources coordinately contribute to individual biological processes under various physiological conditions.
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Hornwort stomata do not respond actively to exogenous and environmental cues.
Pressel, S, Renzaglia, KS, Dicky Clymo, RS, Duckett, JG
Annals of botany. 2018;(1):45-57
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Abstract
BACKGROUNDS AND AIMS Because stomata in bryophytes occur on sporangia, they are subject to different developmental and evolutionary constraints from those on leaves of tracheophytes. No conclusive experimental evidence exists on the responses of hornwort stomata to exogenous stimulation. METHODS Responses of hornwort stomata to abscisic acid (ABA), desiccation, darkness and plasmolysis were compared with those in tracheophyte leaves. Potassium ion concentrations in the guard cells and adjacent cells were analysed by X-ray microanalysis, and the ontogeny of the sporophytic intercellular spaces was compared with those of tracheophytes by cryo-scanning electron microscopy. KEY RESULTS The apertures in hornwort stomata open early in development and thereafter remain open. In hornworts, the experimental treatments, based on measurements of >9000 stomata, produced only a slight reduction in aperture dimensions after desiccation and plasmolysis, and no changes following ABA treatments and darkness. In tracheophytes, all these treatments resulted in complete stomatal closure. Potassium concentrations are similar in hornwort guard cells and epidermal cells under all treatments at all times. The small changes in hornwort stomatal dimensions in response to desiccation and plasmolysis are probably mechanical and/or stress responses of all the epidermal and spongy chlorophyllose cells, affecting the guard cells. In contrast to their nascent gas-filled counterparts across tracheophytes, sporophytic intercellular spaces in hornworts are initially liquid filled. CONCLUSIONS Our experiments demonstrate a lack of physiological regulation of opening and closing of stomata in hornworts compared with tracheophytes, and support accumulating developmental and structural evidence that stomata in hornworts are primarily involved in sporophyte desiccation and spore discharge rather than the regulation of photosynthesis-related gaseous exchange. Our results run counter to the notion of the early acquisition of active control of stomatal movements in bryophytes as proposed from previous experiments on mosses.
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The Xerobranching Response Represses Lateral Root Formation When Roots Are Not in Contact with Water.
Orman-Ligeza, B, Morris, EC, Parizot, B, Lavigne, T, Babé, A, Ligeza, A, Klein, S, Sturrock, C, Xuan, W, Novák, O, et al
Current biology : CB. 2018;(19):3165-3173.e5
Abstract
Efficient soil exploration by roots represents an important target for crop improvement and food security [1, 2]. Lateral root (LR) formation is a key trait for optimizing soil foraging for crucial resources such as water and nutrients. Here, we report an adaptive response termed xerobranching, exhibited by cereal roots, that represses branching when root tips are not in contact with wet soil. Non-invasive X-ray microCT imaging revealed that cereal roots rapidly repress LR formation as they enter an air space within a soil profile and are no longer in contact with water. Transcript profiling of cereal root tips revealed that transient water deficit triggers the abscisic acid (ABA) response pathway. In agreement with this, exogenous ABA treatment can mimic repression of LR formation under transient water deficit. Genetic analysis in Arabidopsis revealed that ABA repression of LR formation requires the PYR/PYL/RCAR-dependent signaling pathway. Our findings suggest that ABA acts as the key signal regulating xerobranching. We conclude that this new ABA-dependent adaptive mechanism allows roots to rapidly respond to changes in water availability in their local micro-environment and to use internal resources efficiently.
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Exogenous strigolactone interacts with abscisic acid-mediated accumulation of anthocyanins in grapevine berries.
Ferrero, M, Pagliarani, C, Novák, O, Ferrandino, A, Cardinale, F, Visentin, I, Schubert, A
Journal of experimental botany. 2018;(9):2391-2401
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Abstract
Besides signalling to soil organisms, strigolactones (SLs) control above- and below-ground morphology, in particular shoot branching. Furthermore, SLs interact with stress responses, possibly thanks to a crosstalk with the abscisic acid (ABA) signal. In grapevine (Vitis vinifera L.), ABA drives the accumulation of anthocyanins over the ripening season. In this study, we investigated the effects of treatment with a synthetic strigolactone analogue, GR24, on anthocyanin accumulation in grape berries, in the presence or absence of exogenous ABA treatment. Experiments were performed both on severed, incubated berries, and on berries attached to the vine. Furthermore, we analysed the corresponding transcript concentrations of genes involved in anthocyanin biosynthesis, and in ABA biosynthesis, metabolism, and membrane transport. During the experiment time courses, berries showed the expected increase in soluble sugars and anthocyanins. GR24 treatment had no or little effect on anthocyanin accumulation, or on gene expression levels. Exogenous ABA treatment activated soluble sugar and anthocyanin accumulation, and enhanced expression of anthocyanin and ABA biosynthetic genes, and that of genes involved in ABA hydroxylation and membrane transport. Co-treatment of GR24 with ABA delayed anthocyanin accumulation, decreased expression of anthocyanin biosynthetic genes, and negatively affected ABA concentration. GR24 also enhanced the ABA-induced activation of ABA hydroxylase genes, while it down-regulated the ABA-induced activation of ABA transport genes. Our results show that GR24 affects the ABA-induced activation of anthocyanin biosynthesis in this non-climacteric fruit. We discuss possible mechanisms underlying this effect, and the potential role of SLs in ripening of non-ABA-treated berries.