Soil salinity is one of the most commonly encountered environmental stresses affecting plant growth and crop productivity. Accordingly, plants have evolved a variety of morphological, physiological ...and biochemical strategies that enable them to adapt to saline growth conditions. For example, it has long been known that salinity-stress increases both the production of the gaseous stress hormone ethylene and the
in planta
accumulation of reactive oxygen species (ROS). Recently, there has been significant progress in understanding how the fine-tuning of ethylene biosynthesis and signaling transduction can promote salinity tolerance, and how salinity-induced ROS accumulation also acts as a signal in the mediation of salinity tolerance. Furthermore, recent advances have indicated that ethylene signaling modulates salinity responses largely via regulation of ROS-generating and ROS-scavenging mechanisms. This review focuses on these recent advances in understanding the linked roles of ethylene and ROS in salt tolerance.
CAM photosynthesis: the acid test Winter, Klaus; Smith, J. Andrew C.
New phytologist,
January 2022, Letnik:
233, Številka:
2
Journal Article
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Summary
There is currently considerable interest in the prospects for bioengineering crassulacean acid metabolism (CAM) photosynthesis – or key elements associated with it, such as increased ...water‐use efficiency – into C3 plants. Resolving how CAM photosynthesis evolved from the ancestral C3 pathway could provide valuable insights into the targets for such bioengineering efforts. It has been proposed that the ability to accumulate organic acids at night may be common among C3 plants, and that the transition to CAM might simply require enhancement of pre‐existing fluxes, without the need for changes in circadian or diurnal regulation. We show, in a survey encompassing 40 families of vascular plants, that nocturnal acidification is a feature entirely restricted to CAM species. Although many C3 species can synthesize malate during the light period, we argue that the switch to night‐time malic acid accumulation requires a fundamental metabolic reprogramming that couples glycolytic breakdown of storage carbohydrate to the process of net dark CO2 fixation. This central element of the CAM pathway, even when expressed at a low level, represents a biochemical capability not seen in C3 plants, and so is better regarded as a discrete evolutionary innovation than as part of a metabolic continuum between C3 and CAM.
Pineapple (Ananas comosus (L.) Merr.) is the most economically valuable crop possessing crassulacean acid metabolism (CAM), a photosynthetic carbon assimilation pathway with high water-use ...efficiency, and the second most important tropical fruit. We sequenced the genomes of pineapple varieties F153 and MD2 and a wild pineapple relative, Ananas bracteatus accession CB5. The pineapple genome has one fewer ancient whole-genome duplication event than sequenced grass genomes and a conserved karyotype with seven chromosomes from before the ρ duplication event. The pineapple lineage has transitioned from C3 photosynthesis to CAM, with CAM-related genes exhibiting a diel expression pattern in photosynthetic tissues. CAM pathway genes were enriched with cis-regulatory elements associated with the regulation of circadian clock genes, providing the first cis-regulatory link between CAM and circadian clock regulation. Pineapple CAM photosynthesis evolved by the reconfiguration of pathways in C3 plants, through the regulatory neofunctionalization of preexisting genes and not through the acquisition of neofunctionalized genes via whole-genome or tandem gene duplication.
High soil Na concentrations damage plants by increasing cellular Na accumulation and K loss. Excess soil Na stimulates ethylene-induced soil-salinity tolerance, the mechanism of which we here define ...via characterization of an Arabidopsis thaliana mutant displaying transpiration-dependent soil-salinity tolerance. This phenotype is conferred by a loss-of-function allele of ETHYLENE OVERPRODUCER1 (ETO1; mutant alleles of which cause increased production of ethylene). We show that lack of ETO1 function confers soil-salinity tolerance through improved shoot Na/K homeostasis, effected via the ETHYLENE RESISTANT1—CONSTITUTIVE TRIPLE RESPONSE1 ethylene signaling pathway. Under transpiring conditions, lack of ETO1 function reduces root Na influx and both stelar and xylem sap Na concentrations, thereby restricting root-to-shoot delivery of Na. These effects are associated with increased accumulation of RESPIRATORY BURST OXIDASE HOMOLOG F (RBOHF)—dependent reactive oxygen species in the root stele. Additionally, lack of ETO1 function leads to significant enhancement of tissue K status by an RBOHF-independent mechanism associated with elevated HIGH-AFFINITY K + TRANSPORTER5 transcript levels. We conclude that ethylene promotes soil-salinity tolerance via improved Na/K homeostasis mediated by RBOHF-dependent regulation of Na accumulation and RBOHF-independent regulation of K accumulation.
Fibroblast growth factor 21 (FGF21) is a novel metabolic regulator that represents a promising target for the treatment of several metabolic diseases. Administration of recombinant wild type FGF21 to ...diabetic animals leads to a dramatic improvement in glycaemia and ameliorates other systemic measures of metabolic health. Here we report the pharmacologic outcomes observed in non-human primates upon administration of a recently described FGF21 analogue, LY2405319 (LY). Diabetic rhesus monkeys were treated subcutaneously with LY once daily for a period of seven weeks. The doses of LY used were 3, 9 and 50 mg/kg each delivered in an escalating fashion with washout measurements taken at 2, 4, 6 and 8 weeks following the final LY dose. LY therapy led to a dramatic and rapid lowering of several important metabolic parameters including glucose, body weight, insulin, cholesterol and triglyceride levels at all doses tested. In addition, we observed favorable changes in circulating profiles of adipokines, with increased adiponectin and reduced leptin indicative of direct FGF21 action on adipose tissue. Importantly, and for the first time we show that FGF21 based therapy has metabolic efficacy in an animal with late stage diabetes. While the glycemic efficacy of LY in this animal was partially attenuated its lipid lowering effect was fully preserved suggesting that FGF21 may be a viable treatment option even in patients with advanced disease progression. These findings support continued exploration of the FGF21 pathway for the treatment of metabolic disease.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The key components of crassulacean acid metabolism (CAM) – nocturnal fixation of atmospheric CO2 and its processing via Rubisco in the subsequent light period – are now reasonably well understood in ...terms of the biochemical reactions defining this water-saving mode of carbon assimilation. Phenotypically, however, the degree to which plants engage in the CAM cycle relative to regular C3 photosynthesis is highly variable. Depending upon species, ontogeny and environment, the contribution of nocturnal CO2 fixation to 24-h carbon gain can range continuously from close to 0% to 100%. Nevertheless, not all possible combinations of light and dark CO2 fixation appear equally common. Large-scale surveys of carbon-isotope ratios typically show a strongly bimodal frequency distribution, with relatively few intermediate values. Recent research has revealed that many species capable of low-level CAM activity are nested within the peak of C3-type isotope signatures. While questions remain concerning the adaptive significance of dark CO2 fixation in such species, plants with low-level CAM should prove valuable models for investigating the discrete changes in genetic architecture and gene expression that have enabled the evolutionary transition from C3 to CAM.
A primary target of the pleiotropic metabolic hormone FGF21 is adipose tissue, where it initiates a gene expression program to enhance energy expenditure, an effect presumed to be centered on ...augmented UCP1 expression and activity. In UCP1 null (UCP1KO) mice, we show that the effect of FGF21 to increase the metabolic rate is abolished. However, in contrast to prior expectations, we found that increased UCP1-dependent thermogenesis is only partially required to achieve the beneficial effects of FGF21 treatment. In UCP1KO mice, there appears to be an underlying reduction in food intake following FGF21 administration, facilitating weight loss equal to that observed in wild-type animals. Furthermore, we show that UCP1-dependent thermogenesis is not required for FGF21 to improve glycemic control or to reduce circulating cholesterol or free fatty acids. These data indicate that several important metabolic endpoints of FGF21 are UCP1 independent; however, the contribution of UCP1-dependent thermogenesis to other discrete aspects of FGF21 biology requires further study.
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•In UCP1KO mice, FGF21 acts to reduce food intake to promote weight loss•The majority of FGF21-driven metabolic endpoints do not require UCP1•FGF21 requires the presence of UCP1 to enhance caloric expenditure in vivo
FGF21 is a metabolic regulator whose effects are associated with increases in UCP1 and energy expenditure. To delineate the contribution of uncoupled respiration to the pharmacology of FGF21, Samms et al. examine its effects in UCP1 null mice. They report that the majority of metabolic effects triggered by FGF21 occur independently of UCP1.
•We trace 97 million years of bromeliad adaptation, biogeography, and species diversification.•We use these data to test an integrative model for bromeliad evolution.•Patterns of correlated and ...contingent evolution are consistent with this model.•Diversification rates are significantly higher in epiphytic, tank-forming, bird-pollinated, and montane lineages.•86% Of bromeliad species richness reflects six major adaptive radiations in different areas.
We present an integrative model predicting associations among epiphytism, the tank habit, entangling seeds, C3 vs. CAM photosynthesis, avian pollinators, life in fertile, moist montane habitats, and net rates of species diversification in the monocot family Bromeliaceae. We test these predictions by relating evolutionary shifts in form, physiology, and ecology to time and ancestral distributions, quantifying patterns of correlated and contingent evolution among pairs of traits and analyzing the apparent impact of individual traits on rates of net species diversification and geographic expansion beyond the ancestral Guayana Shield. All predicted patterns of correlated evolution were significant, and the temporal and spatial associations of phenotypic shifts with orogenies generally accorded with predictions. Net rates of species diversification were most closely coupled to life in fertile, moist, geographically extensive cordilleras, with additional significant ties to epiphytism, avian pollination, and the tank habit. The highest rates of net diversification were seen in the bromelioid tank-epiphytic clade (Dcrown=1.05My−1), associated primarily with the Serra do Mar and nearby ranges of coastal Brazil, and in the core tillandsioids (Dcrown=0.67My−1), associated primarily with the Andes and Central America. Six large-scale adaptive radiations and accompanying pulses of speciation account for 86% of total species richness in the family. This study is among the first to test a priori hypotheses about the relationships among phylogeny, phenotypic evolution, geographic spread, and net species diversification, and to argue for causality to flow from functional diversity to spatial expansion to species diversity.
Circulating branched-chain amino acid (BCAA) levels are elevated in obesity/diabetes and are a sensitive predictor for type 2 diabetes. Here we show in rats that insulin dose-dependently lowers ...plasma BCAA levels through induction of hepatic protein expression and activity of branched-chain α-keto acid dehydrogenase (BCKDH), the rate-limiting enzyme in the BCAA degradation pathway. Selective induction of hypothalamic insulin signaling in rats and genetic modulation of brain insulin receptors in mice demonstrate that brain insulin signaling is a major regulator of BCAA metabolism by inducing hepatic BCKDH. Short-term overfeeding impairs the ability of brain insulin to lower BCAAs in rats. High-fat feeding in nonhuman primates and obesity and/or diabetes in humans is associated with reduced BCKDH protein in liver. These findings support the concept that decreased hepatic BCKDH is a major cause of increased plasma BCAAs and that hypothalamic insulin resistance may account for impaired BCAA metabolism in obesity and diabetes.
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•Insulin, but not glucose, is a major regulator of circulating BCAAs•Hypothalamic insulin lowers plasma BCAAs and induces hepatic BCAA catabolism•Acute overfeeding impairs the ability of brain insulin to lower circulating BCAAs•High-fat feeding in primates or obese/diabetic humans decreases hepatic BCKDH
Circulating branched-chain amino acid (BCAA) levels are elevated in obesity and diabetes. Shin et al. describe a brain insulin pathway that decreases BCAA levels by enhancing its degradation in the liver. High-fat-fed rodents and nonhuman primates, as well as diabetics, have reduced amounts of the enzyme responsible for degradation.
Premise: Bromeliaceae form a large, ecologically diverse family of angiosperms native to the New World. We use a bromeliad phylogeny based on eight plastid regions to analyze relationships within the ...family, test a new, eight-subfamily classification, infer the chronology of bromeliad evolution and invasion of different regions, and provide the basis for future analyses of trait evolution and rates of diversification. Methods: We employed maximum-parsimony, maximum-likelihood, and Bayesian approaches to analyze 9341 aligned bases for four outgroups and 90 bromeliad species representing 46 of 58 described genera. We calibrate the resulting phylogeny against time using penalized likelihood applied to a monocot-wide tree based on plastid ndhF sequences and use it to analyze patterns of geographic spread using parsimony, Bayesian inference, and the program S-DIVA. Results: Bromeliad subfamilies are related to each other as follows: (Brocchinioideae, (Lindmanioideae, (Tillandsioideae, (Hechtioideae, (Navioideae, (Pitcairnioideae, (Puyoideae, Bromelioideae))). Bromeliads arose in the Guayana Shield ca. 100 million years ago (Ma), spread centrifugally in the New World beginning ca. 16–13 Ma, and dispersed to West Africa ca. 9.3 Ma. Modern lineages began to diverge from each other roughtly 19 Ma. Conclusions: Nearly two-thirds of extant bromeliads belong to two large radiations: the core tillandsioids, originating in the Andes ca. 14.2 Ma, and the Brazilian Shield bromelioids, originating in the Serro do Mar and adjacent regions ca. 9.1 Ma.
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