Explore the vast range of titles available.

A carotenoid-derived hormonal signal that inhibits shoot branching in plants has long escaped identification. Strigolactonesare compounds thought to be derived from carotenoids and are known to trigger the germination of parasitic plant seeds andstimulate symbiotic fungi. Here we present evidence that carotenoid cleavage dioxygenase 8 shoot branching mutants of peaare strigolactone deficient and that strigolactone application restores the wild-type branching phenotype to ccd8 mutants.Moreover, we show that other branching mutants previously characterized as lacking a response to the branching inhibitionsignal also lack strigolactone response, and are not deficient in strigolactones. These responses are conserved in Arabidopsis.In agreement with the expected properties of the hormonal signal, exogenous strigolactone can be transported in shoots andact at low concentrations. We suggest that endogenous strigolactones or related compounds inhibit shoot branching inplants. Furthermore, ccd8 mutants demonstrate the diverse effects of strigolactones in shoot branching, mycorrhizalsymbiosis and parasitic weed interaction.

Shoot branching is a major determinant of plant architecture and is highly regulated by endogenous and environmental cues. Two classes of hormones, auxin and cytokinin, have long been known to have an important involvement in controlling shoot branching. Previous studies using a series of mutants with enhanced shoot branching suggested the existence of a third class of hormone(s) that is derived from carotenoids, but its chemical identity has been unknown. Here we show that levels of strigolactones, a group of terpenoid lactones, are significantly reduced in some of the branching mutants. Furthermore, application of strigolactones inhibits shoot branching in these mutants. Strigolactones were previously found in root exudates acting as communication chemicals with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Thus, we propose that strigolactones act as a new hormone class—or their biosynthetic precursors—in regulating above-ground plant architecture, and also have a function in underground communication with other neighbouring organisms. Branching out: new class of plant hormones inhibits branch formation For many years the textbooks recognized five 'classic' plant hormones: auxin, gibberellins, ethylene, cytokinin and abscisic acid. To these can be added the brassinosteroids, nitric oxide and jasmonates, among others, as phytohormones or plant growth regulators. Shoot branching is regulated by hormones, with both auxin and cytokinin playing a part. But the existence of mutants with enhanced branching in several species suggested a third factor was involved, a novel plant hormone released from the roots that prevents excessive shoot branching. Two groups now identify a class of chemical compounds called strigolactones — or one of their derivatives — as that missing hormone. Strigolactones are found in root exudates and are reduced in the branching mutants; external application of these chemicals inhibits shoot branching in the mutants. Shoot branching is regulated by hormones. Branching mutants in several plant species suggests the existence of a plant hormone that is released from the roots and prevents excessive shoot branching. This paper reports on one of two studies that show that a class of chemical compounds called strigolactones found in root exudates are reduced in the branching mutants and that external application of these chemicals inhibits shoot branching in the mutants. It is proposed that strigolactones or related metabolites are the sought after class of hormones.

Inactivation of the phytohormone auxin plays important roles in plant development, and several enzymes have been implicated in auxin inactivation. In this study, we show that the predominant natural auxin, indole-3-acetic acid (IAA), is mainly inactivated via the GH3-ILR1-DAO pathway. IAA is first converted to IAA-amino acid conjugates by GH3 IAA-amidosynthetases. The IAA-amino acid conjugates IAA-aspartate (IAA-Asp) and IAA-glutamate (IAA-Glu) are storage forms of IAA and can be converted back to IAA by ILR1/ILL amidohydrolases. We further show that DAO1 dioxygenase irreversibly oxidizes IAA-Asp and IAA-Glu into 2-oxindole-3-acetic acid-aspartate (oxIAA-Asp) and oxIAA-Glu, which are subsequently hydrolyzed by ILR1 to release inactive oxIAA. This work established a complete pathway for the oxidative inactivation of auxin and defines the roles played by auxin homeostasis in plant development. Auxin inactivation plays important roles in plant development. Here the authors show that the main route of IAA inactivation in Arabidopsis is via conjugation by GH3 IAA-amidosynthetases followed by DAO1 dioxygenase-mediated oxidation of the conjugated forms and hydrolysis by ILR1 to release inactive oxIAA.

Canola, a vital oilseed crop, is grown globally for food and biodiesel. With the enormous demand for growing various crops, the utilization of agriculturally marginal lands is emerging as an attractive alternative, including brackish-saline transitional lands. Salinity is a major abiotic stress limiting growth and productivity of most crops, and causing food insecurity. Salicylic acid (SA), a small-molecule phenolic compound, is an essential plant defense phytohormone that promotes immunity against pathogens. Recently, several studies have reported that SA was able to improve plant resilience to withstand high salinity. For this purpose, a pot experiment was carried out to ameliorate the negative effects of sodium chloride (NaCl) on canola plants through foliar application of SA. Two canola varieties Faisal (V1) and Super (V2) were assessed for their growth performance during exposure to high salinity i.e. 0 mM NaCl (control) and 200 mM NaCl. Three levels of SA (0, 10, and 20 mM) were applied through foliar spray. The experimental design used for this study was completely randomized design (CRD) with three replicates. The salt stress reduced the shoot and root fresh weights up to 50.3% and 47% respectively. In addition, foliar chlorophyll a and b contents decreased up to 61–65%. Meanwhile, SA treatment diminished the negative effects of salinity and enhanced the shoot fresh weight (49.5%), root dry weight (70%), chl. a (36%) and chl. b (67%). Plants treated with SA showed an increased levels of both enzymatic i.e. (superoxide dismutase (27%), peroxidase (16%) and catalase (34%)) and non-enzymatic antioxidants i.e. total soluble protein (20%), total soluble sugar (17%), total phenolic (22%) flavonoids (19%), anthocyanin (23%), and endogenous ascorbic acid (23%). Application of SA also increased the levels of osmolytes i.e. glycine betaine (31%) and total free proline (24%). Salinity increased the concentration of Na + ions and concomitantly decreased the K + and Ca 2+ absorption in canola plants. Overall, the foliar treatments of SA were quite effective in reducing the negative effects of salinity. By comparing both varieties of canola, it was observed that variety V2 (Super) grew better than variety V1 (Faisal). Interestingly, 20 mM foliar application of SA proved to be effective in ameliorating the negative effects of high salinity in canola plants.

932 I. 932 II. 933 III. 934 IV. 938 V. 941 943 References 943 SUMMARY: Next to numerous abiotic stresses, plants are constantly exposed to a variety of pathogens within their environment. Thus, their ability to survive and prosper during the course of evolution was strongly dependent on adapting efficient strategies to perceive and to respond to such potential threats. It is therefore not surprising that modern plants have a highly sophisticated immune repertoire consisting of diverse signal perception and intracellular signaling pathways. This signaling network is intricate and deeply interconnected, probably reflecting the diverse lifestyles and infection strategies used by the multitude of invading phytopathogens. Moreover it allows signal communication between developmental and defense programs thereby ensuring that plant growth and fitness are not significantly retarded. How plants integrate and prioritize the incoming signals and how this information is transduced to enable appropriate immune responses is currently a major research area. An important finding has been that pathogen‐triggered cellular responses involve massive transcriptional reprogramming within the host. Additional key observations emerging from such studies are that transcription factors (TFs) are often sites of signal convergence and that signal‐regulated TFs act in concert with other context‐specific TFs and transcriptional co‐regulators to establish sensory transcription regulatory networks required for plant immunity.

Seed germination and postgerminative growth are regulated by a delicate hormonal balance. Abscisic acid (ABA) represses Arabidopsis thaliana seed germination and postgerminative growth, while brassinosteroids (BRs) antagonize ABA-mediated inhibition and promote these processes. However, the molecular mechanism underlying BR-repressed ABA signaling remains largely unknown. Here, we show that the Glycogen Synthase Kinase 3-like kinase BRASSINOSTEROID INSENSITIVE2 (BIN2), a critical repressor of BR signaling, positively regulates ABA responses during seed germination and postgerminative growth. Mechanistic investigation revealed that BIN2 physically interacts with ABSCISIC ACID INSENSITIVE5 (ABI5), a bZIP transcription factor. Further genetic analysis demonstrated that the ABA-hypersensitive phenotype of BIN2-overexpressing plants requires ABI5. BIN2 was found to phosphorylate and stabilize ABI5 in the presence of ABA, while application of epibrassinolide (the active form of BRs) inhibited the regulation of ABI5 by BIN2. Consistently, the ABA-induced accumulation of ABI5 was affected in BIN2-related mutants. Moreover, mutations of the BIN2 phosphorylation sites on ABI5 made the mutant protein respond to ABA improperly. Additionally, the expression of several ABI5 regulons was positively modulated by BIN2. These results provide evidence that BIN2 phosphorylates and stabilizes ABI5 to mediate ABA response during seed germination, while BRs repress the BIN2-ABI5 cascade to antagonize ABA-mediated inhibition.

Key message5-aminolevulinic acid (ALA) modulates various defense systems in plants and confers abiotic stress tolerance.Enhancement of crop production is a challenge due to numerous abiotic stresses such as, salinity, drought, temperature, heavy metals, and UV. Plants often face one or more abiotic stresses in their life cycle because of the challenging growing environment which results in reduction of growth and yield. Diverse studies have been conducted to discern suitable mitigation strategies to enhance crop production by minimizing abiotic stress. Exogenous application of different plant growth regulators is a well-renowned approach to ameliorate adverse effects of abiotic stresses on crop plants. Among the numerous plant growth regulators, 5-aminolevulinic acid (ALA) is a novel plant growth regulator, also well-known to alleviate the injurious effects of abiotic stresses in plants. ALA enhances abiotic stress tolerance as well as growth and yield by regulating photosynthetic and antioxidant machineries and nutrient uptake in plants. However, the regulatory roles of ALA in plants under different stresses have not been studied and assembled systematically. Also, ALA-mediated abiotic stress tolerance mechanisms have not been fully elucidated yet. Therefore, this review discusses the role of ALA in crop growth enhancement as well as its ameliorative role in abiotic stress mitigation and also discusses the ALA-mediated abiotic stress tolerance mechanisms and its limitation and future promises for sustainable crop production.

Jasmonates are a family of plant hormones that regulate plant growth, development and responses to stress. The F-box protein CORONATINE INSENSITIVE 1 (COI1) mediates jasmonate signalling by promoting hormone-dependent ubiquitylation and degradation of transcriptional repressor JAZ proteins. Despite its importance, the mechanism of jasmonate perception remains unclear. Here we present structural and pharmacological data to show that the true Arabidopsis jasmonate receptor is a complex of both COI1 and JAZ. COI1 contains an open pocket that recognizes the bioactive hormone (3 R ,7 S )-jasmonoyl- l -isoleucine (JA-Ile) with high specificity. High-affinity hormone binding requires a bipartite JAZ degron sequence consisting of a conserved α-helix for COI1 docking and a loop region to trap the hormone in its binding pocket. In addition, we identify a third critical component of the jasmonate co-receptor complex, inositol pentakisphosphate, which interacts with both COI1 and JAZ adjacent to the ligand. Our results unravel the mechanism of jasmonate perception and highlight the ability of F-box proteins to evolve as multi-component signalling hubs. Three-part receptor for jasmonate plant hormones The receptors for several important plant hormones have been identified in recent years, including those for auxin, the gibberellins and abscisic acid, and structure–function studies have revealed their mechanisms of action. Now the mechanism by which plant cells recognize the jasmonate phytohormones — key players in growth regulation, development and defence responses — is reported. The jasmonate receptor is a three-molecule complex consisting of the F-box protein COI1, a JAZ (JASMONATE ZIM DOMAIN) transcriptional repressor, and inositol pentakisphosphate. All three receptor components are required for high-affinity hormone binding. This system for jasmonate perception involves mechanisms that are distinct from those of the other plant hormones studied so far, although all depend on hormone-mediated protein interactions. The F-box protein CORONATINE INSENSITIVE 1 (COI1) mediates jasmonate signalling by promoting hormone-dependent ubiquitylation and degradation of the JASMONATE ZIM DOMAIN (JAZ) family of transcriptional repressors. These authors elucidate the mechanism of jasmonate perception. They present structural and pharmacological data to show that the true jasmonate receptor is a complex of both COI1 and JAZ. In addition, inositol pentakisphosphate functions as a critical component of the hormone receptor complex.

N-1-naphthylphthalamic acid (NPA) is a key inhibitor of directional (polar) transport of the hormone auxin in plants. For decades, it has been a pivotal tool in elucidating the unique polar auxin transportbased processes underlying plant growth and development. Its exact mode of action has long been sought after and is still being debated, with prevailing mechanistic schemes describing only indirect connections between NPA and the main transporters responsible for directional transport, namely PIN auxin exporters. Here we present data supporting a model in which NPA associates with PINs in a more direct manner than hitherto postulated. We show that NPA inhibits PIN activity in a heterologous oocyte system and that expression of NPA-sensitive PINs in plant, yeast, and oocyte membranes leads to specific saturable NPA binding. We thus propose that PINs are a bona fide NPA target. This offers a straightforward molecular basis for NPA inhibition of PIN-dependent auxin transport and a logical parsimonious explanation for the known physiological effects of NPA on plant growth, as well as an alternative hypothesis to interpret past and future results. We also introduce PIN dimerization and describe an effect of NPA on this, suggesting that NPA binding could be exploited to gain insights into structural aspects of PINs related to their transport mechanism.

Nanocarrier systems for the encapsulation of agrochemicals can contribute to sustainable agriculture, but few nanosystems have been developed for plant growth regulators (PGRs). The present study evaluated the effects of seed priming using alginate/chitosan ( nano ALG/CS) and chitosan/tripolyphosphate ( nano CS/TPP) containing GA 3 on the growth and productivity of Solanum lycopersicum cultivated under field conditions. The results demonstrated that nanocarrier systems could improve fruit production, with the productivity increasing almost 4-fold using nano ALG/CS-GA 3 . This pioneering study demonstrates the potential of nanocarrier systems with PGRs for applications in agriculture.