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The multinational Arabidopsis research community is highly collaborative and over the past thirty years these activities have been documented by the Multinational Arabidopsis Steering Committee (MASC). Here, we (a) highlight recent research advances made with the reference plant Arabidopsis thaliana; (b) provide summaries from recent reports submitted by MASC subcommittees, projects and resources associated with MASC and from MASC country representatives; and (c) initiate a call for ideas and foci for the "fourth decadal roadmap," which will advise and coordinate the global activities of the Arabidopsis research community.

Plant roots exert hydrotropism in response to moisture gradients to avoid drought stress. The regulatory mechanism underlying hydrotropism involves novel regulators such as MIZ1 and GNOM/MIZ2 as well as abscisic acid (ABA), reactive oxygen species (ROS), and Ca2+ signaling. ABA, ROS, and Ca2+ signaling are also involved in plant responses to drought stress. Although the mechanism of moisture gradient perception remains largely unknown, the sensory apparatus has been reported to reside in the root elongation zone rather than in the root cap. In Arabidopsis roots, hydrotropism is mediated by the action of MIZ1 and ABA in the cortex of the elongation zone, the accumulation of ROS at the root curvature, and the variation in the cytosolic Ca2+ concentration in the entire root tip including the root cap and stele of the elongation zone. Moreover, root exposure to moisture gradients has been proposed to cause asymmetric ABA distribution or Ca2+ signaling, leading to the induction of the hydrotropic response. A comprehensive and detailed analysis of hydrotropism regulators and their signaling network in relation to the tissues required for their function is apparently crucial for understanding the mechanisms unique to root hydrotropism. Here, referring to studies on plant responses to drought stress, we summarize the recent findings relating to the role of ABA, ROS, and Ca2+ signaling in hydrotropism, discuss their functional sites and plausible networks, and raise some questions that need to be answered in future studies. [ABSTRACT FROM AUTHOR]

Electron flow through the electron transport chain (ETC) is essential for oxidative phosphorylation in mitochondria and photosynthesis in chloroplasts. Electron fluxes depend on environmental parameters, e.g., ionic and osmotic conditions and endogenous factors, and this may cause severe imbalances. Plants have evolved alternative sinks to balance the reductive load on the electron transport chains in order to avoid overreduction, generation of reactive oxygen species (ROS), and to cope with environmental stresses. These sinks act primarily as valves for electron drainage and secondarily as regulators of tolerance‐related metabolism, utilizing the excess reductive energy. High salinity is an environmental stressor that stimulates the generation of ROS and oxidative stress, which affects growth and development by disrupting the redox homeostasis of plants. While glycophytic plants are sensitive to high salinity, halophytic plants tolerate, grow, and reproduce at high salinity. Various studies have examined the ETC systems of glycophytic plants, however, information about the state and regulation of ETCs in halophytes under non‐saline and saline conditions is scarce. This review focuses on alternative electron sinks in chloroplasts and mitochondria of halophytic plants. In cases where information on halophytes is lacking, we examined the available knowledge on the relationship between alternative sinks and gradual salinity resilience of glycophytes. To this end, transcriptional responses of involved components of photosynthetic and respiratory ETCs were compared between the glycophyte Arabidopsis thaliana and the halophyte Schrenkiella parvula, and the time‐courses of these transcripts were examined in A. thaliana. The observed regulatory patterns are discussed in the context of reactive molecular species formation in halophytes and glycophytes. [ABSTRACT FROM AUTHOR]

Single cell C4 (SCC4) plants, discovered around two decades ago, are promising materials for efforts for genetic engineering of C4 photosynthesis into C3 crops. Unlike C4 plants with Kranz anatomy, they exhibit a fully functional C4 photosynthesis in just a single cell and do not require mesophyll and bundle sheath cell spatial separation. Bienertia sinuspersici is one such SCC4 plant, with NAD-malic enzyme (NAD-ME) subtype C4 photosynthesis. Its chlorenchyma cell consist of two compartments, peripheral compartment (PC), analogous to mesophyll cell, and central compartment (CC), analogous to bundle sheath cell. Since oxidative stress creates an important constraint for plants under salinity and drought, we comparatively examined the response of enzymatic antioxidant system, H2O2 and TBARS contents, peroxiredoxin Q, NADPH thioredoxin reductase C, and plastid terminal oxidase protein levels of PC chloroplasts (PCC) and CC chloroplasts (CCC). Except for protein levels, these parameters were also examined on the whole leaf level, as well as catalase and NADPH oxidase activities, water status and growth parameters, and levels of C4 photosynthesis related transcripts. Many C4 photosynthesis related transcript levels were elevated, especially under drought. Activities of dehydroascorbate reductase and especially peroxidase were elevated under drought in both compartments (CCC and PCC). Even though decreases of antioxidant enzyme activities were more prevalent in PCC, and the examined redox regulating protein levels, especially of peroxiredoxin Q, were elevated in CCC under both stresses, PCC was less damaged by either stress. These suggest PCC is more tolerant and has other means of preventing or alleviating oxidative damage. [ABSTRACT FROM AUTHOR]

Achieving food security and sustainable food production is a major challenge for plant scientists. To accomplish this, the global food production needs not only to be remarkably boosted, but it has to be achieved under harsh environmental conditions. Moreover, the climate change scenarios estimate an enhanced pressure on crop yields in the upcoming decades. C4 photosynthesis is highly promising to meet these challenges to global food production. Under current CO2 levels, C4 photosynthesis is more efficient than C3 photosynthesis, but more data is needed to map out its response under elevated CO2 (eCO2) conditions. Growing evidence also suggests that C4 photosynthesis could be more efficient in water use under eCO2. Production of reactive oxygen species (ROS) is an inevitable consequence of oxygenic photosynthesis and is also one of the first responses to environmental stresses. C3 and C4 plants have different ROS profiles, mainly because of reduced photorespiration in the latter. Moreover, the effects of eCO2 on C3 and especially C4 plants remain poorly understood. Since C3 and C4 plants have different ROS production patterns, it is likely that ROS signalling and downstream effects on growth and development differ between C3 and C4 plants, which may result in different response to eCO2. This would also be reflected in reproductive success and crop yields. Here we evaluate the recent literature on C3 and C4 plant responses to climate change conditions from the abiotic stress tolerance and food security perspectives, with redox connections. Current body of knowledge suggests engineering C4 photosynthesis into major crops to be a viable way to increase yield, but such attempts have failed because of a lack of basic knowledge in this area. Therefore, this article also aims to fill this gap from the redox perspective. [ABSTRACT FROM AUTHOR]

Aim of this work was to investigate effects of toxic levels of Cu, Zn and Fe treatments on small ubiquitinlike modifier (SUMO) machinery of Arabidopsis thaliana. SUMO is a 100-115 amino acid posttranslational modifier that can regulate stability, activity or sub-cellular localization of target proteins. A. thaliana plants were treated with 50 µM Cu, 700 µM Zn and 400 µM Fe for 7 d and then expressions of genes related to SUMOylation and deSUMOylation of target proteins were measured with qRT-PCR. Only Cu treatment was able to induce genes related to SUMOylation (SUM3, SAE2, SIZ1) of target proteins, while all of the three metals used in this study was effective in inducing a deSUMOylation related gene. Results of this study indicate that deSUMOylation of proteins might be a part of plant response to metal toxicity. [ABSTRACT FROM AUTHOR]

The element arsenic (As) is a non-essential metalloid that is found naturally in all soils and at high concentrations it is toxic to plant cells. As (V) can act as a chemical analogue of phosphate, it can disrupt phosphate-related energy metabolism and lipid structure. In this study, the contribution of mitochondrial alternative oxidase (AOX) and chloroplastic plastid terminal oxidase (PTOX) to As (V) stress tolerance was investigated. Our data indicate that As (V) stress (100, 200 and 300 µM) induces AOX gene expression by 3.3- to 10.5-fold depending on AOX gene, but not PTOX expression in wild-type A. thaliana plants. To further elucidate the role of AOX in As (V) stress tolerance, we utilized aox1a mutants and observed that aox1a mutants had decreased growth and higher oxidative stress damage under stress conditions, while there were no differences under control conditions. Moreover, acclimation of aox1a plants to new cellular redox environment was investigated by measuring the activities of reactive oxygen species (ROS)-scavenging enzymes. Induction of mitochondrial MnSOD activity at 300 µM As (V) was higher in aox1a plants (70%), when compared to wild type (43%). However, total ascorbate peroxidase and dehydroascorbate reductase activities were lower in aox1a plants when compared to wild type, which might explain higher oxidative damage observed in this genotype. On the other hand, NADPH oxidase activity, which is involved in ROS signaling, was lower in aox1a plants under normal conditions but a higher induction was observed with As (V) stress. Overall, our data indicate that AOX1a is involved in adaptation to As (V)-induced oxidative stress. [ABSTRACT FROM AUTHOR]

Redox regulation, antioxidant defence, and reactive oxygen species (ROS) signalling are critical in performing and tuning metabolic activities. However, our concepts have mostly been developed for C3 plants since Arabidopsis thaliana has been the major model for research. Efforts to convert C3 plants to C4 to increase yield (such as IRRI's C4 Rice Project) entail a better understanding of these processes in C4 plants. Various photosynthetic enzymes that take part in light reactions and carbon reactions are regulated via redox components, such as thioredoxins as redox transmitters and peroxiredoxins. Hence, understanding redox regulation in the mesophyll and bundle sheath chloroplasts of C4 plants is of paramount importance: it appears impossible to utilize efficient C4 photosynthesis without understanding its exact redox needs and the regulation mechanisms used during light reactions. In this review, we discuss current knowledge on redox regulation in C3 and C4 plants, with special emphasis on the mesophyll and bundle sheath differences that are found in C4. In these two cell types in C4 plants, linear and cyclic electron transport in the chloroplasts operate differentially when compared to C3 chloroplasts, changing the redox needs of the cell. Therefore, our focus is on photosynthetic light reactions, ROS production dynamics, antioxidant defence, and thiol-based redox regulation, with the aim of providing an overview of our current knowledge. [ABSTRACT FROM AUTHOR]

Bienertia sinuspersici performs single cell C 4 photosynthesis without Kranz anatomy. Peripheral and central cytoplasmic compartments in a single chlorenchyma cell act as mesophyll cells and bundle sheath cells. Development of this specialized mechanism is gradual during plant development. Young leaves perform C 3 photosynthesis, while mature leaves have complete C 4 cycle. The aim of this work was to investigate changes in redox regulation and antioxidant defence during transition from C 3 to single cell C 4 photosynthesis in B. sinuspersici leaves. First, we confirmed gradual development of C 4 with protein blot and qRT-PCR analysis of C 4 enzymes. After this activities and isoenzymes of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and H 2 O 2 and TBARS and glutathione pool and redox status (GSH/GSSG) were determined in young, developing and mature leaves during transition from C 3 to single cell C 4 photosynthesis. Activities of SOD, APX and POX decrease, while GR and DHAR were increased. However, most striking results were the changes in isoenzyme patterns of SOD, CAT and GR which were gradual through transition to C 4 photosynthesis. [ABSTRACT FROM AUTHOR]

C 4 plants are acclimated to drought and high temperatures that are detrimental for C 3 plants, and they are well equipped with a better antioxidant capacity to cope with oxidative stress caused by abiotic stresses. However, how C 3 and C 4 plants respond to oxidative stress that occurs in a specific compartment of the cell, such as chloroplast or mitochondria, is still not known. Therefore, understanding antioxidant responses of different carboxylation pathways to reactive oxygen species (ROS) at organelle level deserves an investigation. In the present study, the production of organelle originated ROS was induced with chemical agents specific to mitochondria (rotenone =ROT) and chloroplasts (methyl viologen = MV and DCMU), and antioxidant response of Flaveria robusta (C 3) and F. bidentis (C 4) were studied. For this purpose, activities of antioxidant system (superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductases (GR)), and isoenzymes of SOD, CAT, and NADPH oxidase (NOX) activity were determined. Treatment of leaves with ROT, MV and DCMU for 4 h induced lipid peroxidation by 38%, 18% and 41% respectively in F. robusta , while 81%, 75% and 56% induction were observed for same inhibitors in F. bidentis. On the other hand, treatment with inhibitors cause decrease of CAT activity in F. robusta (27% with ROT), while increased CAT activity was observed in F. bidentis (maximum 68% with MV). Overall, the antioxidant defense responses of C 3 and C 4 plants were distinctive to organelle induced oxidative stress, especially in chloroplast-sourced accumulation of ROS. • Response to organellar oxidative stress was studied in C 3 and C 4 species of Flaveria. • Methyl viologen, rotenone and DCMU was used to induce organellar oxidative stress. • Flaveria bidentis (C 4) was more sensitive after 4 h treatment as evident by lipid peroxidation. • F. robusta (C 3) CAT activity decreased, while it was increased in Flaveria bidentis (C 4). • Antioxidant responses of C 3 and C 4 species were distinctive to organellar oxidative stress. [ABSTRACT FROM AUTHOR]