Metabolite profiling and quantitative genetics of natural variation for flavonoids in Arabidopsis

Little is known about the range and the genetic bases of naturally occurring variation for flavonoids. Using Arabidopsis thaliana seed as a model, the flavonoid content of 41 accessions and two recombinant inbred line (RIL) sets derived from divergent accessions (Cvi-0×Col-0 and Bay-0×Shahdara) were analysed. These accessions and RILs showed mainly quantitative rather than qualitative changes. To dissect the genetic architecture underlying these differences, a quantitative trait locus (QTL) analysis was performed on the two segregating populations. Twenty-two flavonoid QTLs were detected that accounted for 11–64% of the observed trait variations, only one QTL being common to both RIL sets. Sixteen of these QTLs were confirmed and coarsely mapped using heterogeneous inbred families (HIFs). Three genes, namely TRANSPARENT TESTA (TT)7, TT15, and MYB12, were proposed to underlie their variations since the corresponding mutants and QTLs displayed similar specific flavonoid changes. Interestingly, most loci did not co-localize with any gene known to be involved in flavonoid metabolism. This latter result shows that novel functions have yet to be characterized and paves the way for their isolation

Overexpression of the class D MADS-box gene Sl-AGL11 impacts fleshy tissue differentiation and structure in tomato fruits

MADS-box transcription factors are key elements of the genetic networks controlling flower and fruit development. Among these, the class D clade gathers AGAMOUS-like genes which are involved in seed, ovule, and funiculus development. The tomato genome comprises two class D genes, Sl-AGL11 and Sl-MBP3 , both displaying high expression levels in seeds and in central tissues of young fruits. The potential effects of Sl-AGL11 on fruit development were addressed through RNAi silencing and ectopic expression strategies. Sl-AGL11-down-regulated tomato lines failed to show obvious phenotypes except a slight reduction in seed size. In contrast, Sl-AGL11 overexpression triggered dramatic modifications of flower and fruit structure that include: the conversion of sepals into fleshy organs undergoing ethylene-dependent ripening, a placenta hypertrophy to the detriment of locular space, starch and sugar accumulation, and an extreme softening that occurs well before the onset of ripening. RNA-Seq transcriptomic profiling high-lighted substantial metabolic reprogramming occurring in sepals and fruits, with major impacts on cell wall-related genes. While several Sl-AGL11-related phenotypes are reminiscent of class C MADS-box genes (TAG1 and TAGL1), the modifications observed on the placenta and cell wall and the Sl-AGL11 expression pattern suggest an action of this class D MADS-box factor on early fleshy fruit development

Activite et modes d'actions de nouvelles series de molecules a potentialite herbicide

SIGLEINIST T 75981 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Trienoic fatty acids and plant tolerance of temperature

The biophysical reactions of light harvesting and electron transport during photosynthesis take place in a uniquely constructed bilayer, the thylakoid. In all photosynthetic eukaryotes, the complement of atypical glycerolipid molecules that form the foundation of this membrane are characterised by sugar head-groups and a very high level of unsaturation in the fatty acids that occupy the central portion of the thylakoid bilayer. alpha-linolenic (18:3) or a combination of 18:3 and hexadecatrienoic (16:3) acids typically account for approximately two-thirds of all thylakoid membrane fatty acids and over 90% of the fatty acids of monogalactosyl diacylglycerol, the major thylakoid lipid [1, 2]. The occurrence of trienoic fatty acids as a major component of the thylakoid membrane is especially remarkable since these fatty acids form highly reactive targets for active oxygen species and free radicals, which are often the by-products of oxygenic photosynthesis. Photosynthesis is one of the most temperature-sensitive functions of plant [3, 4]. There remains a widespread belief that these trienoic fatty acids might have some crucial role in plants to be of such universal occurrence, especially in photosynthesis tolerance of temperature [5]

Trienoic fatty acids and plant tolerance of temperature

The biophysical reactions of light harvesting and electron transport during photosynthesis take place in a uniquely constructed bilayer, the thylakoid. In all photosynthetic eukaryotes, the complement of atypical glycerolipid molecules that form the foundation of this membrane are characterised by sugar head-groups and a very high level of unsaturation in the fatty acids that occupy the central portion of the thylakoid bilayer. alpha-linolenic (18:3) or a combination of 18:3 and hexadecatrienoic (16:3) acids typically account for approximately two-thirds of all thylakoid membrane fatty acids and over 90% of the fatty acids of monogalactosyl diacylglycerol, the major thylakoid lipid [1, 2]. The occurrence of trienoic fatty acids as a major component of the thylakoid membrane is especially remarkable since these fatty acids form highly reactive targets for active oxygen species and free radicals, which are often the by-products of oxygenic photosynthesis. Photosynthesis is one of the most temperature-sensitive functions of plant [3, 4]. There remains a widespread belief that these trienoic fatty acids might have some crucial role in plants to be of such universal occurrence, especially in photosynthesis tolerance of temperature [5]

Potent non-protonophore uncouplers acting on natural and artificial membranes

The uncoupling properties of 10 new symmetrical phenylureas, including N,N′-bis-(4-trifluoromethylphenyl)-urea, were investigated. Four compounds were shown to be powerful uncouplers. The result is a proton transfer across the organelle's membrane. These symmetrical phenylureas cannot be classified among the main class of uncouplers (acting through a protonophoric mechanism), due to their inability to exchange protons in a range of pHs between 2 and 9. The most potent uncouplers of the series induced permeabilization of artificial bilayer membranes (without protein) to both H+ and monovalent cations (K+, Na+) and did not increase the rate of diffusion of a small uncharged molecule (urea). The uncoupling properties for such molecules are due neither to their ability to induce conformational changes in membrane protein nor to their effect on phospholipid bilayer fluidity. They seem to change the regular organization of the polar lipid bilayer

Trienoic Fatty Acids Are Required to Maintain Chloroplast Function at Low Temperatures

The chloroplast membranes of all higher plants contain very high proportions of trienoic fatty acids. To investigate how these lipid structures are important in photosynthesis, we have generated a triple mutant line of Arabidopsis that contains negligible levels of trienoic fatty acids. For mutant plants grown at 22°C, photosynthetic fluorescence parameters were indistinguishable from wild type at 25°C. Lowering the measurement temperature led to a small decrease in photosynthetic quantum yield, Φ(II), in the mutant relative to wild-type controls. These and other results indicate that low temperature has only a small effect on photosynthesis in the short term. However, long-term growth of plants at 4°C resulted in decreases in fluorescence parameters, chlorophyll content, and thylakoid membrane content in triple-mutant plants relative to wild type. Comparisons among different mutant lines indicated that these detrimental effects of growth at 4°C are strongly correlated with trienoic fatty acid content with levels of 16:3 + 18:3, approximately one-third of wild type being sufficient to sustain normal photosynthetic function. In total, our results indicate that trienoic fatty acids are important to ensure the correct biogenesis and maintenance of chloroplasts during growth of plants at low temperatures

Seed development, dormancy and germination. Annual Plant Reviews, Volume 27.

Two major types of dormancy mechanisms exist: embryo dormancy where the agents inhibiting germination are inherent to the embryo, and coat-imposed dormancy where inhibition is conferred by the seed envelopes (Bewley, 1997). Generally, complex interactions between the embryo and covering structures determine whether a seed will germinate. As a consequence, many intermediate situations are encountered due to varying contributions by the embryo and envelopes to dormancy. Seed dormancy is a typical quantitative genetic character involving many genes and being substantially influenced by environmental effects (Koornneef et al., 2002; Alonso-Blanco et al., 2003). It is an adaptative trait allowing germination to occur during the most suitable period for seedling establishment and life cycle completion. Embryo growth potential and characteristics of the seed envelopes that determine theintrinsic capacity of a seed to germinate are established during development. The purpose of this review is to analyze the role of the seed envelopes, particularly the testa (seed coat), in dormancy and germination. The developmental events leading to the formation of the testa in Arabidopsis are presented. Special attention is paid to the roles played by flavonoids, particularly proanthocyanidins (condensed tannins), in determining the physicochemical characteristics of the testa that influence seed dormancy, germination and longevity in various species. In particular, the recent progress made in this field using the model plant Arabidopsis, which also illustrates the power of molecular genetics combined with physiology, is emphasized to dissect the mechanisms of seed coat-imposed dormancy

Potent non-protonophore uncouplers acting on natural and artificial membranes

International audienceThe uncoupling properties of 10 new symmetrical phenylureas, including N,N′-bis-(4-trifluoromethylphenyl)-urea, were investigated. Four compounds were shown to be powerful uncouplers. The result is a proton transfer across the organelle's membrane. These symmetrical phenylureas cannot be classified among the main class of uncouplers (acting through a protonophoric mechanism), due to their inability to exchange protons in a range of pHs between 2 and 9. The most potent uncouplers of the series induced permeabilization of artificial bilayer membranes (without protein) to both H+ and monovalent cations (K+, Na+) and did not increase the rate of diffusion of a small uncharged molecule (urea). The uncoupling properties for such molecules are due neither to their ability to induce conformational changes in membrane protein nor to their effect on phospholipid bilayer fluidity. They seem to change the regular organization of the polar lipid bilayer

Influence of zeaxanthin and echinenone binding on the activity of the Orange Carotenoid Protein

In most cyanobacteria high irradiance induces a photoprotective mechanism that downregulates photosynthesis by increasing thermal dissipation of the energy absorbed by the phycobilisome, the watersoluble antenna. The light activation of a soluble carotenoid protein, the Orange-Carotenoid-Protein (OCP), binding hydroxyechinenone, a keto carotenoid, is the key inducer of this mechanism. Light causes structural changes within the carotenoid and the protein, leading to the conversion of a dark orange form into a red active form. Here, we tested whether echinenone or zeaxanthin can replace hydroxyechinenone in a study in which the nature of the carotenoid bound to the OCP was genetically changed. In a mutant lacking hydroxyechinenone and echinenone, the OCP was found to bind zeaxanthin but the stability of the binding appeared to be lower and light was unable to photoconvert the dark form into a red active form. Moreover, in the strains containing zeaxanthin-OCP, blue-green light did not induce the photoprotective mechanism. In contrast, in mutants in which echinenone is bound to the OCP, the protein is photoactivated and photoprotection is induced. Our results strongly suggest that the presence of the carotenoid carbonyl group that distinguishes echinenone and hydroxyechinenone from zeaxanthin is essential for the OCP activity