Arabidopsis mutants reveal that short- and long-term thermotolerance have different requirements for trienoic fatty acids

The photosynthetic thylakoid has the highest level of lipid unsaturation of any membrane. In Arabidopsis thaliana plants grown at 22°C, approximately 70% of the thylakoid fatty acids are trienoic – they have three double bonds. In Arabidopsis, and other species, the levels of trienoic fatty acids decline substantially at higher temperatures. Several genetic studies indicate that reduced unsaturation improves photosynthetic function and plant survival at high temperatures. Here, these studies are extended using the Arabidopsis triple mutant, fad3-2 fad7-2 fad8 that contains no detectable trienoic fatty acids. In the short-term, fluorescence analyses and electron-transport assays indicated that photosynthetic functions in this mutant are more thermotolerant than the wild type. However, long-term photosynthesis, growth, and survival of plants were all compromised in the triple mutant at high temperature. The fad3-2 fad7-2 fad8 mutant is deficient in jasmonate synthesis and this hormone has been shown to mediate some aspects of thermotolerance; however, additional experiments demonstrated that a lack of jasmonate was not a major factor in the death of triple-mutant plants at high temperature. The results indicate that long-term thermotolerance requires a basal level of trienoic fatty acids. Thus, the success of genetic and molecular approaches to increase thermotolerance by reducing membrane unsaturation will be limited by countervailing effects that compromise essential plant functions at elevated temperatures

Proanthocyanidin oxidation of Arabidopsis seeds is altered in mutant of the high-affinity nitrate transporter NRT2.7

This article appears in:Special Issue: Nutrient Sensing and SignallingNRT2.7 is a seed-specific high-affinity nitrate transporter controlling nitrate content in Arabidopsis mature seeds. The objective of this work was to analyse further the consequences of the nrt2.7 mutation for the seed metabolism. This work describes a new phenotype for the nrt2.7-2 mutant allele in the Wassilewskija accession, which exhibited a distinctive pale-brown seed coat that is usually associated with a defect in flavonoid oxidation. Indeed, this phenotype resembled those of tt10 mutant seeds defective in the laccase-like enzyme TT10/LAC15, which is involved in the oxidative polymerization of flavonoids such as the proantocyanidins (PAs) (i.e. epicatechin monomers and PA oligomers) and flavonol glycosides. nrt2.7-2 and tt10-2 mutant seeds displayed the same higher accumulation of PAs, but were partially distinct, since flavonol glycoside accumulation was not affected in the nrt2.7-2 seeds. Moreover, measurement of in situ laccase activity excluded a possibility of the nrt2.7-2 mutation affecting the TT10 enzymic activity at the early stage of seed development. Functional complementation of the nrt2.7-2 mutant by overexpression of a full-length NRT2.7 cDNA clearly demonstrated the link between the nrt2.7 mutation and the PA phenotype. However, the PA-related phenotype of nrt2.7-2 seeds was not strictly correlated to the nitrate content of seeds. No correlation was observed when nitrate was lowered in seeds due to limited nitrate nutrition of plants or to lower nitrate storage capacity in leaves of clca mutants deficient in the vacuolar anionic channel CLCa. All together, the results highlight a hitherto-unknown function of NRT2.7 in PA accumulation/oxidation.Laure C. David, Julie Dechorgnat, Patrick Berquin, Jean Marc Routaboul, Isabelle Debeaujon, Françoise Daniel-Vedele and Sylvie Ferrario-Mér

Arabidopsis Fatty Acid Desaturase FAD2 Is Required for Salt Tolerance during Seed Germination and Early Seedling Growth

Fatty acid desaturases play important role in plant responses to abiotic stresses. However, their exact function in plant resistance to salt stress is unknown. In this work, we provide the evidence that FAD2, an endoplasmic reticulum localized ω-6 desaturase, is required for salt tolerance in Arabidopsis. Using vacuolar and plasma membrane vesicles prepared from the leaves of wild-type (Col-0) and the loss-of-function Arabidopsis mutant, fad2, which lacks the functional FAD2, we examined the fatty acid composition and Na+-dependent H+ movements of the isolated vesicles. We observed that, when compared to Col-0, the level of vacuolar and plasma membrane polyunsaturation was lower, and the Na+/H+ exchange activity was reduced in vacuolar and plasma membrane vesicles isolated from fad2 mutant. Consistent with the reduced Na+/H+ exchange activity, fad2 accumulated more Na+ in the cytoplasm of root cells, and was more sensitive to salt stress during seed germination and early seedling growth, as indicated by CoroNa-Green staining, net Na+ efflux and salt tolerance analyses. Our results suggest that FAD2 mediated high-level vacuolar and plasma membrane fatty acid desaturation is essential for the proper function of membrane attached Na+/H+ exchangers, and thereby to maintain a low cytosolic Na+ concentration for salt tolerance during seed germination and early seedling growth in Arabidopsis

Evolutionary view of acyl-CoA diacylglycerol acyltransferase (DGAT), a key enzyme in neutral lipid biosynthesis

<p>Abstract</p> <p>Background</p> <p>Triacylglycerides (TAGs) are a class of neutral lipids that represent the most important storage form of energy for eukaryotic cells. DGAT (acyl-CoA: diacylglycerol acyltransferase; EC 2.3.1.20) is a transmembrane enzyme that acts in the final and committed step of TAG synthesis, and it has been proposed to be the rate-limiting enzyme in plant storage lipid accumulation. In fact, two different enzymes identified in several eukaryotic species, DGAT1 and DGAT2, are the main enzymes responsible for TAG synthesis. These enzymes do not share high DNA or protein sequence similarities, and it has been suggested that they play non-redundant roles in different tissues and in some species in TAG synthesis. Despite a number of previous studies on the DGAT1 and DGAT2 genes, which have emphasized their importance as potential obesity treatment targets to increase triacylglycerol accumulation, little is known about their evolutionary timeline in eukaryotes. The goal of this study was to examine the evolutionary relationship of the DGAT1 and DGAT2 genes across eukaryotic organisms in order to infer their origin.</p> <p>Results</p> <p>We have conducted a broad survey of fully sequenced genomes, including representatives of Amoebozoa, yeasts, fungi, algae, musses, plants, vertebrate and invertebrate species, for the presence of DGAT1 and DGAT2 gene homologs. We found that the DGAT1 and DGAT2 genes are nearly ubiquitous in eukaryotes and are readily identifiable in all the major eukaryotic groups and genomes examined. Phylogenetic analyses of the DGAT1 and DGAT2 amino acid sequences revealed evolutionary partitioning of the DGAT protein family into two major DGAT1 and DGAT2 clades. Protein secondary structure and hydrophobic-transmembrane analysis also showed differences between these enzymes. The analysis also revealed that the MGAT2 and AWAT genes may have arisen from DGAT2 duplication events.</p> <p>Conclusions</p> <p>In this study, we identified several DGAT1 and DGAT2 homologs in eukaryote taxa. Overall, the data show that DGAT1 and DGAT2 are present in most eukaryotic organisms and belong to two different gene families. The phylogenetic and evolutionary analyses revealed that DGAT1 and DGAT2 evolved separately, with functional convergence, despite their wide molecular and structural divergence.</p

Expansión posterior con resortes y avance fronto-orbitario simultáneo en craneosinostosis sindrómicas Spring-assisted posterior expansion and simultaneous fronto-orbitary expansion in syndromic cranyosinostosis

Las craneoestenosis sindrómicas son anomalías congénitas de difícil resolución y requieren generalmente varios procedimientos quirúrgicos. La expansión posterior de la calota permite disminuir la hipertensión endocraneana y sus efectos sobre el cerebro. La utilización de resortes para la expansión posterior ha demostrado ser un método efectivo y estable, disminuyendo la morbilidad de los procedimientos tradicionales. La combinación de la expansión posterior con resortes y el avance frontoorbitario en una sola etapa, antes del año de vida, disminuye el número de intervenciones necesarias obteniéndose una buena remodelación de la bóveda craneana. Presentamos nuestra experiencia en 3 casos de craneoestenosis sindrómica mediante la realización simultánea de ambos procedimientos con buenos resultados estéticos y funcionales.Syndromic craniosynostosis is a difficult-to-resolve congenital anomaly generally requiring several surgical procedures. Expansion of the posterior cranial vault diminishes intracranial hypertension and its deleterious effect on the brain. The use of spring-assisted distraction for posterior vault expansion showed to be an effective and stable method with lower morbidity than that seen in traditional procedures. The combination of spring-assisted posterior vault expansion and fronto-orbital advancement in a single stage before one year of life decreases the number of surgical interventions necessary and leads to adequate remodeling of the cranial vault. Here we present 3 cases of syndromic craniosynostosis who simultaneously underwent both procedures with good esthetic and functional results

Stability and conformation of methyl urocanates and their N-methyl derivatives. Analysis by molecular mechanics (MM2) and semi-empirical computations (PM3)

Molecular mechanics (MM2(87)) and semi-empirical computation (PM3) showed that the majority species of the E and Z isomers of methyl urocanates is the protonated form, at least in vacuo and probably in neutral and aprotic media as well.Competition between the N1 and N3 nitrogen atoms on N-methylation is analyzed and discussed. The 1H NMR data were interpreted on the basis of conformations that are accessible at room temperature. A change in conformation of the Z isomer accompanying the alteration in site of methylation can account for the marked change in chemical shift of the C4 proton