Autophagic Machinery of Plant Peroxisomes

Peroxisomes are cell organelles that play an important role in plants in many physiological and developmental processes. The plant peroxisomes harbor enzymes of the β-oxidation of fatty acids and the glyoxylate cycle; photorespiration; detoxification of reactive oxygen and nitrogen species; as well as biosynthesis of hormones and signal molecules. The function of peroxisomes in plant cells changes during plant growth and development. They are transformed from organelles involved in storage lipid breakdown during seed germination and seedling growth into leaf peroxisomes involved in photorespiration in green parts of the plant. Additionally, intensive oxidative metabolism of peroxisomes causes damage to their components. Therefore, unnecessary or damaged peroxisomes are degraded by selective autophagy, called pexophagy. This is an important element of the quality control system of peroxisomes in plant cells. Despite the fact that the mechanism of pexophagy has already been described for yeasts and mammals, the molecular mechanisms by which plant cells recognize peroxisomes that will be degraded via pexophagy still remain unclear. It seems that a plant-specific mechanism exists for the selective degradation of peroxisomes. In this review, we describe the physiological role of pexophagy in plant cells and the current hypotheses concerning the mechanism of plant pexophagy

Transgenic plants as a source of high quality oils

Oleje roślinne są niezwykle istotnym, odnawialnym źródłem pożywienia człowieka i paszy dla zwierząt oraz znajdują wielorakie zastosowania przemysłowe. Zwiększające się zapotrzebowanie ze strony przemysłu zarówno spożywczego jak i niespożywczego na oleje roślinne i ich składniki wymusza poszukiwania nowych, efektywniejszych i ekonomiczniejszych źródeł ich pozyskiwania. Współcześnie nie wystarczy tylko zwiększenie areału upraw roślin oleistych, ale konieczne są też inne przedsięwzięcia prowadzące do uzyskania nowych odmian. Odmian zarówno akumulujących więcej oleju ale też odmian, które zdolne są do biosyntezy związków naturalnie w nich niewystępujących bądź występujących w śladowych ilościach. W tego typu badaniach sięga się po dobrze znane, powszechnie uprawiane rośliny użytkowe takie jak rzepak czy soja. Jednak w zdecydowanej większości, prace nad nowymi odmianami roślin transgenicznych zaczynają się od badań prowadzonych na roślinie modelowej, jaką jest Arabidopsis thaliana. W niniejszym opracowaniu przedstawiono szereg przykładów roślin modyfikowanych genetycznie, w których uzyskano wzrost zawartości akumulowanego oleju, zmodyfikowano skład oleju pod kątem diety człowieka jak również wymuszono syntezę wielu związków wartościowych dla przemysłu. Przytoczono również liczne przykłady zastosowań przemysłowych dla olejów roślinnych i ich składników. Jednym z celów tego opracowania jest pokazanie wielokierunkowości badań mających doprowadzić do uzyskania nowych genetycznie modyfikowanych odmian cechujących się zmienionym metabolizmem tłuszczowym.Vegetable oils represent a very important, renewable source of human food, animal feed and have multiple industrial applications. Increasing demand from both food and non-food industry for vegetable oils and their components forces the search for new, more efficient and more economical sources of their acquisition. Today, it is not enough just to increase the acreage of oil plants; there is a need for projects leading to the creation of new varieties. The new varieties should either accumulate more oil or can be capable of biosynthesis of compounds that naturally do not occur in their tissues or are present in trace amounts. In this kind of research well-known commonly used crops such as oilseed rape and soybean are included. However, the vast majority of works on new varieties of transgenic plants start from research conducted on the model plant Arabidopsis thaliana. This paper presents several examples of genetically modified plants with increased oil level, modified oil composition regarding human diet, and with constrained synthesis of many compounds valuable to the industry. Numerous examples of industrial applications for vegetable oils and their components are presented. One of the aims of this paper is demonstration that plurality of research lead to new genetically modified varieties with modified lipid metabolism

Vacuolar Processing Enzymes in Plant Programmed Cell Death and Autophagy

Vacuolar processing enzymes (VPEs) are plant cysteine proteases that are subjected to autoactivation in an acidic pH. It is presumed that VPEs, by activating other vacuolar hydrolases, are in control of tonoplast rupture during programmed cell death (PCD). Involvement of VPEs has been indicated in various types of plant PCD related to development, senescence, and environmental stress responses. Another pathway induced during such processes is autophagy, which leads to the degradation of cellular components and metabolite salvage, and it is presumed that VPEs may be involved in the degradation of autophagic bodies during plant autophagy. As both PCD and autophagy occur under similar conditions, research on the relationship between them is needed, and VPEs, as key vacuolar proteases, seem to be an important factor to consider. They may even constitute a potential point of crosstalk between cell death and autophagy in plant cells. This review describes new insights into the role of VPEs in plant PCD, with an emphasis on evidence and hypotheses on the interconnections between autophagy and cell death, and indicates several new research opportunities

Completing Autophagy: Formation and Degradation of the Autophagic Body and Metabolite Salvage in Plants

Autophagy is an evolutionarily conserved process that occurs in yeast, plants, and animals. Despite many years of research, some aspects of autophagy are still not fully explained. This mostly concerns the final stages of autophagy, which have not received as much interest from the scientific community as the initial stages of this process. The final stages of autophagy that we take into consideration in this review include the formation and degradation of the autophagic bodies as well as the efflux of metabolites from the vacuole to the cytoplasm. The autophagic bodies are formed through the fusion of an autophagosome and vacuole during macroautophagy and by vacuolar membrane invagination or protrusion during microautophagy. Then they are rapidly degraded by vacuolar lytic enzymes, and products of the degradation are reused. In this paper, we summarize the available information on the trafficking of the autophagosome towards the vacuole, the fusion of the autophagosome with the vacuole, the formation and decomposition of autophagic bodies inside the vacuole, and the efflux of metabolites to the cytoplasm. Special attention is given to the formation and degradation of autophagic bodies and metabolite salvage in plant cells

New Insight into Plant Signaling: Extracellular ATP and Uncommon Nucleotides

New players in plant signaling are described in detail in this review: extracellular ATP (eATP) and uncommon nucleotides such as dinucleoside polyphosphates (NpnN’s), adenosine 5′-phosphoramidate (NH2-pA), and extracellular NAD+ and NADP+ (eNAD(P)+). Recent molecular, physiological, and biochemical evidence implicating concurrently the signaling role of eATP, NpnN’s, and NH2-pA in plant biology and the mechanistic events in which they are involved are discussed. Numerous studies have shown that they are often universal signaling messengers, which trigger a signaling cascade in similar reactions and processes among different kingdoms. We also present here, not described elsewhere, a working model of the NpnN’ and NH2-pA signaling network in a plant cell where these nucleotides trigger induction of the phenylpropanoid and the isochorismic acid pathways yielding metabolites protecting the plant against various types of stresses. Through these signals, the plant responds to environmental stimuli by intensifying the production of various compounds, such as anthocyanins, lignin, stilbenes, and salicylic acid. Still, more research needs to be performed to identify signaling networks that involve uncommon nucleotides, followed by omic experiments to define network elements and processes that are controlled by these signals

Sugar Starvation Disrupts Lipid Breakdown by Inducing Autophagy in Embryonic Axes of Lupin (Lupinus spp.) Germinating Seeds

Under nutrient deficiency or starvation conditions, the mobilization of storage compounds during seed germination is enhanced to primarily supply respiratory substrates and hence increase the potential of cell survival. Nevertheless, we found that, under sugar starvation conditions in isolated embryonic axes of white lupin (Lupinus albus L.) and Andean lupin (Lupinus mutabilis Sweet) cultured in vitro for 96 h, the disruption of lipid breakdown occurs, as was reflected in the higher lipid content in the sugar-starved (-S) than in the sucrose-fed (+S) axes. We postulate that pexophagy (autophagic degradation of the peroxisome—a key organelle in lipid catabolism) is one of the reasons for the disruption in lipid breakdown under starvation conditions. Evidence of pexophagy can be: (i) the higher transcript level of genes encoding proteins of pexophagy machinery, and (ii) the lower content of the peroxisome marker Pex14p and its increase caused by an autophagy inhibitor (concanamycin A) in -S axes in comparison to the +S axes. Additionally, based on ultrastructure observation, we documented that, under sugar starvation conditions lipophagy (autophagic degradation of whole lipid droplets) may also occur but this type of selective autophagy seems to be restricted under starvation conditions. Our results also show that autophagy occurs at the very early stages of plant growth and development, including the cells of embryonic seed organs, and allows cell survival under starvation conditions