1,721,046 research outputs found
Using genetic tools to understand plant phosphoinositide signalling
No full textPhosphoinositides (Pis) are regulatory lipids that control various physiological processes in eukaryotic organisms. As in other eukaryotes, the plant Pi system is a central regulator of metabolism. The analysis of mutant plants that lack certain Pi species has revealed their physiological relevance; however, knowledge of the factors controlling the distribution of Pis and the effects on their target proteins is still limited. To understand Pi functions better, genetic approaches should be combined with biochemical analyses and cell biology, as has been done in several recent publications. Here, I highlight plant-specific physiological processes that are controlled by Pis and suggest future avenues of research. A detailed understanding of the functions and effects of Pis might offer new opportunities for modulating plant growth and hardiness against environmental influences
Male functions and malfunctions: the impact of phosphoinositides on pollen development and pollen tube growth
No full textIn angiosperms, sexual reproduction is a series of complex biological events that facilitate the distribution of male generative cells for double fertilization. Angiosperms have no motile gametes, and the distribution units of generative cells are pollen grains, passively mobile desiccated structures, capable of delivering genetic material to compatible flowers over long distances and in an adverse environment. The development of pollen (male gametogenesis) and the formation of a pollen tube after a pollen grain has reached a compatible flower (pollen tube growth) are important aspects of plant developmental biology. In recent years, a wealth of information has been gathered about the molecular control of cell polarity, membrane trafficking and cytoskeletal dynamics underlying these developmental processes. In particular, it has been found that regulatory membrane phospholipids, such as phosphoinositides (PIs), are critical regulatory players, controlling key steps of trafficking and polarization. Characteristic features of PIs are the inositol phosphate headgroups of the lipids, which protrude from the cytosolic surfaces of membranes, enabling specific binding and recruitment of numerous protein partners containing specific PI-binding domains. Such recruitment is globally an early event in polarization processes of eukaryotic cells and also of key importance to pollen development and tube growth. Additionally, PIs serve as precursors of other signaling factors with importance to male gametogenesis. This review highlights the recent advances about the roles of PIs in pollen development and pollen function
Stress-inducible and constitutive phosphoinositide pools have distinctive fatty acid patterns in Arabidopsis thaliana
No full textFunction and development of eukaryotic cells require tight control of diverse physiological processes. Numerous cellular processes are regulated by polyphosphoinositides, which interact with protein partners or mediate release of the second messenger, inositol 1,4,5-trisphosphate (InsP3). Emerging evidence suggests that different regulatory or signaling functions of polyphosphoinositides may be orchestrated by the establishment of distinct subcellular pools; the principles underlying pool-formation are, however, not understood. Arabidopsis plants exhibit transient increases in polyphosphoinositides with hyperosmotic stress, providing a model for comparing constitutive and stress-inducible polyphosphoinositide pools. Using a combination of thin-layer-chromatography and gaschromatography, phospholipids from stressed and nonstressed Arabidopsis plants were analyzed for their associated fatty acids. Under nonstress conditions structural phospholipids and phosphatidylinositol contained 50-70 mol% polyunsaturated fatty acids (PUFA), whereas polyphosphoinositides were more saturated (10-20 mol% PUFA). With hyperosmotic stress polyphosphoinositides with up to 70 mol% PUFA were formed that differed from constitutive species and coincided with a transient loss in unsaturated phosphatidylinositol. The patterns indicate inducible turnover of an unsaturated phosphatidylinositol pool, which accumulates under standard conditions and is primed for phosphorylation on stimulation. Metabolic analysis of wild-type and transgenic plants disturbed in phosphoinositide metabolism suggests that, in contrast to saturated species, unsaturated polyphosphoinositides are channeled toward InsP3-production
Type B Phosphatidylinositol-4-Phosphate 5-Kinases Mediate Arabidopsis and Nicotiana tabacum Pollen Tube Growth by Regulating Apical Pectin Secretion
No full textPhosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P(2)] occurs in the apical plasma membrane of growing pollen tubes. Because enzymes responsible for PtdIns(4,5) P(2) production at that location are uncharacterized, functions of PtdIns( 4,5) P(2) in pollen tube tip growth are unresolved. Two candidate genes encoding pollen-expressed Arabidopsis thaliana phosphatidylinositol-4-phosphate 5-kinases (PI4P 5-kinases) of Arabidopsis subfamily B were identified (PIP5K4 and PIP5K5), and their recombinant proteins were characterized as being PI4P 5-kinases. Pollen of T-DNA insertion lines deficient in both PIP5K4 and PIP5K5 exhibited reduced pollen germination and defects in pollen tube elongation. Fluorescence-tagged PIP5K4 and PIP5K5 localized to an apical plasma membrane microdomain in Arabidopsis and tobacco (Nicotiana tabacum) pollen tubes, and overexpression of either PIP5K4 or PIP5K5 triggered multiple tip branching events. Further studies using the tobacco system revealed that overexpression caused massive apical pectin deposition accompanied by plasma membrane invaginations. By contrast, callose deposition and cytoskeletal structures were unaltered in the overexpressors. Morphological effects depended on PtdIns(4,5) P(2) production, as an inactive enzyme variant did not produce any effects. The data indicate that excessive PtdIns(4,5) P2 production by type B PI4P 5-kinases disturbs the balance of membrane trafficking and apical pectin deposition. Polar tip growth of pollen tubes may thus be modulated by PtdIns(4,5) P(2) via regulatory effects on membrane trafficking and/or apical pectin deposition.German Research Foundatio
Oxylipins: Structurally diverse metabolites from fatty acid oxidation
No full textOxylipins are lipophilic signaling molecules derived from the oxidation of polyunsaturated fatty acids. Initial fatty acid oxidation occurs mainly by the enzymatic or chemical formation of fatty acid hydroperoxides. An array of alternative reactions further converting fatty acid hydroperoxides gives rise to a multitude of oxylipin classes, many with reported signaling functions in plants. Oxylipins include the phytohormone, jasmonic acid, and a number of other molecules including hydroxy-, oxo- or keto-fatty acids or volatile aldehydes that may perform various biological roles as second messengers, messengers in inter-organismic signaling, or even as bactericidal agents. The structural diversity of oxylipins is further increased by esterification of the compounds in plastidial glycolipids, for instance the Arabidopsides, or by conjugation of oxylipins to amino acids or other metabolites. The enzymes involved in oxylipin metabolism are diverse and comprise a multitude of examples with interesting and unusual catalytic properties. In addition, the interplay of different subcellular compartments during oxylipin biosynthesis suggests complex mechanisms of regulation that are not well understood. This review aims at giving an overview of plant oxylipins and the multitude of enzymes responsible for their biosynthesis. (C) 2008 Elsevier Masson SAS. All rights reserved
Determination of content and fatty acid composition of unlabeled phosphoinositide species by thin-layer chromatography and gas chromatography
No full textRecent advances in research on the physiological roles of phosphoinositides in eukaryotic organisms indicate a need to distinguish molecular phosphoinositide species on the basis of their characteristic head groups as well as their glycerolipid moieties. Accurate identification of phosphoinositide species in biological samples poses an analytical challenge, because structurally similar inositol phosphate head groups must be resolved, as must lipid-associated fatty acids. Although intact phosphoinositide species have been successfully analyzed, such analyses employ state-of-the-art liquid chromatography/mass spectrometry and require expensive equipment not accessible to many researchers. Described here is a cost-efficient and reliable alternative developed by adaptation of a combination of classic methods for lipid analysis, thin-layer chromatography and gas chromatography. (C) 2008 Elsevier Inc. All rights reserved
Oxylipin Signaling and Plant Growth
No full textOxylipins are derived from the oxidation of polyunsaturated fatty acids. Further conversion of the resulting fatty acid hydroperoxides gives rise to a multitude of oxylipin classes, including hydroxy-, oxo-, or keto fatty acids, volatile aldehydes, and the phytohormone, jasmonic acid (JA). Oxylipins may be structurally further diversified by esterification, i.e., to plastidial glycolipids, Arabidopsides, or conjugation to amino acids. Oxylipin research so far has focused mainly on the investigation of jasmonates and their roles in wound signaling and plant development. In contrast, the physiological roles of other oxylipins are by far less well understood, in part because enzymes responsible for their formation are not well characterized. This chapter aims at giving an overview of plant oxylipin signaling, highlighting recent discoveries of new roles for different oxylipins in the regulation of developmental or adaptational processes
At the poles across kingdoms: phosphoinositides and polar tip growth
Full text linkPhosphoinositides (PIs) are minor, but essential phospholipid constituents of eukaryotic membranes, and are involved in the regulation of various physiological processes. Recent genetic and cell biological advances indicate that PIs play important roles in the control of polar tip growth in plant cells. In root hairs and pollen tubes, PIs control directional membrane trafficking required for the delivery of cell wall material and membrane area to the growing tip. So far, the exact mechanisms by which PIs control polarity and tip growth are unresolved. However, data gained from the analysis of plant, fungal and animal systems implicate PIs in the control of cytoskeletal dynamics, ion channel activity as well as vesicle trafficking. The present review aims at giving an overview of PI roles in eukaryotic cells with a special focus on functions pertaining to the control of cell polarity. Comparative screening of plant and fungal genomes suggests diversification of the PI system with increasing organismic complexity. The evolutionary conservation of the PI system among eukaryotic cells suggests a role for PIs in tip growing cells in models where PIs so far have not been a focus of attention, such as fungal hyphae
Jasmonic acid perception by COI1 involves inositol polyphosphates in Arabidopsis thaliana
No full textPlant responses to wounding are part of their defense responses against insects, and are tightly regulated. The isoleucin conjugate of jasmonic acid (JA-IIe) is a major regulatory molecule. We have previously shown that inositol polyphosphate signals are required for defense responses in Arabidopsis; however, the way in which inositol polyphosphates contribute to plant responses to wounding has so far remained unclear. Arabidopsis F-box proteins involved in the perception of JA-IIe (COI1) and auxin (TIR1) are structurally similar. Because TIR1 has recently been shown to contain inositol hexakisphosphate (InsP(6)) as a co-factor of unknown function, here we explored the possibility that InsP(6) or another inositol polyphosphate is required for COI1 function. In support of this hypothesis, COI1 variants with changes in putative inositol polyphosphate coordinating residues exhibited a reduced interaction with the COI1 target, JAZ9, in yeast two-hybrid tests. The equivalent COI1 variants displayed a reduced capability to rescue jasmonate-mediated root growth inhibition or silique development in Arabidopsis col1 mutants. Yeast two-hybrid tests using wild-type COI1 in an ipk1 Delta yeast strain exhibiting increased levels of inositol pentakisphosphate (InsP(5)) and reduced levels of InsP(6) indicate an enhanced COI1/JAZ9 interaction. Consistent with these findings, Arabidopsis ipk1-1 mutants, also with increased InsP(5) and reduced InsP(6) levels, showed increased defensive capabilities via COI1-mediated processes, including wound-induced gene expression, defense against caterpillars or root growth inhibition by jasmonate. The combined data from experiments using mutated COI1 variants, as well as yeast and Arabidopsis backgrounds altered in inositol polyphosphate metabolism, indicate that an inositol polyphosphate, and probably InsP(5), contributes to COI1 function
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