Chloroplast lipid biosynthesis is fine-tuned to thylakoid membrane remodeling during light acclimation

Gibberellin biosynthesis gene ScGA20 oxidase enhances sugarcane growth by modulating genes associated with phytohormone and growth processes

Sugarcane is a globally significant crop for sugar and energy production, yet its breeding potential is limited by its complex genetic background and restricted genetic diversity. Molecular breeding presents a promising approach to boost sugarcane productivity. Gibberellins (GA) plays a critical role in plant growth and development, with GA20-oxidase being the most crucial enzyme in GA biosynthesis. In this study, we isolated the sugarcane gene encoding GA20-oxidase (ScGA20ox, OR283803) enzyme, a 43.88 kDa hydrophilic protein, and introduced it into sugarcane variety GT42 via biolistics transformation. Transgenic sugarcane expressing Ubi-driven ScGA20ox exhibited elevated GA levels and accelerated growth. Transcriptome analysis revealed that genes associated with plant hormone metabolism and growth-related pathways, including photosynthesis, plant hormone signal transduction, and starch and sucrose metabolism were involved in the GA20ox-mediated growth in sugarcane. This work underscores the potential of GA20ox for enhancing sugarcane yields through transgenic approaches, while advancing our understanding of GA's regulatory role in the growth of this crucial sugar crop.

Dynamic Membrane Lipid Changes in Physcomitrium patens Reveal Developmental and Environmental Adaptations

Membrane lipid composition is critical for an organism's growth, adaptation, and functionality. Mosses, as early non-vascular land colonizers, show significant adaptations and changes, but their dynamic membrane lipid alterations remain unexplored. Here, we investigated the temporal changes in membrane lipid composition of the moss Physcomitrium patens during five developmental stages and analyzed the acyl content and composition of the lipids. We observed a gradual decrease in total lipid content from the filamentous protonema stage to the reproductive sporophytes. Notably, we found significant levels of very long-chain polyunsaturated fatty acids, particularly arachidonic acid (C20:4), which are not reported in vascular plants and may aid mosses in cold and abiotic stress adaptation. During vegetative stages, we noted high levels of galactolipids, especially monogalactosyldiacylglycerol, associated with chloroplast biogenesis. In contrast, sporophytes displayed reduced galactolipids and elevated phosphatidylcholine and phosphatidic acid, which are linked to membrane integrity and environmental stress protection. Additionally, we observed a gradual decline in the average double bond index across all lipid classes from the protonema stage to the gametophyte stage. Overall, our findings highlight the dynamic nature of membrane lipid composition during moss development, which might contribute to its adaptation to diverse growth conditions, reproductive processes, and environmental challenges.

All members of the Arabidopsis DGAT and PDAT acyltransferase families operate during high and low temperatures

The accumulation of triacylglycerol (TAG) in vegetative tissues is necessary to adapt to changing temperatures. It has been hypothesized that TAG accumulation is required as a storage location for maladaptive membrane lipids. The TAG acyltransferase family has five members (DIACYLGLYCEROL ACYLTRANSFERSE1/2/3 and PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE1/2), and their individual roles during temperature challenges have either been described conflictingly or not at all. Therefore, we used Arabidopsis (Arabidopsis thaliana) loss of function mutants in each acyltransferase to investigate the effects of temperature challenge on TAG accumulation, plasma membrane integrity, and temperature tolerance. All mutants were tested under one high- and two low-temperature regimens, during which we quantified lipids, assessed temperature sensitivity, and measured plasma membrane electrolyte leakage. Our findings revealed reduced effectiveness in TAG production during at least one temperature regimen for all acyltransferase mutants compared to the wild type, resolved conflicting roles of pdat1 and dgat1 by demonstrating their distinct temperature-specific actions, and uncovered that plasma membrane integrity and TAG accumulation do not always coincide, suggesting a multifaceted role of TAG beyond its conventional lipid reservoir function during temperature stress.

Lipids: A noteworthy role in better tea quality

New shoots from tea plants (Camellia sinensis) are changed into finished tea after the process, which endows the products with a characteristic flavor. Tea quality is reflected in all aspects, from new shoots to the finished tea that are affected by cultivar, cultivation condition, harvest season, manufacturing methods, and quality of fresh tea leaves. Lipids are hydrophobic metabolites connected with tea flavor quality formation. Herein, we emphasize that the lipids composition in preharvest tea leaves is crucial for materials quality and hence tea flavor. The characterization of lipids in preharvest tea leaves provides a reference to obtain better tea quality. Lipids transformation in postharvest stages of tea leaves differs from varieties of tea types, and lipid oxidations functions in the tea flavor formation. A comprehensive overview of the lipids in tea leaves of preharvest and postharvest stages is necessary to improve tea quality.

Modulation of plant photosynthetic processes during metal and metalloid stress, and strategies for manipulating photosynthesis-related traits

Metals constitute vital elements for plant metabolism and survival, acting as essential co-factors in cellular processes which are indispensable for plant growth and survival. Excess or deficient provision of metal/metalloids puts plant's life and survival at risk, thus considered a potent stress for plants. Chloroplasts as an organelle with a high metal demand form a pivotal site within the metal homeostasis network. Therefore, the metal-mediated electron transport chain (ETC) in chloroplasts is a primary target site of metal/metalloid-induced stresses. Both excess and deficient availability of metal/metalloids threatens plant's photosynthesis in several ways. Energy demands from the photosynthetic carbon reactions should be in balance with energy output of ETC. Malfunctioning of ETC components as a result of metal/metalloid stress initiates photoinhiition. A feedback inhibition from carbon fixation process also impedes the ETC. Metal stress impairs antioxidant enzyme activity, pigment biosynthesis, and stomatal function. However, genetic manipulations, nutrient management, keeping photostasis, and application of phytohormones are among strategies for coping with metal stress. Consequently, a comprehensive understanding of the underlying mechanisms of metal/metalloid stress, as well as the exploration of potential strategies to mitigate its impact on plants are imperative. This review offers a mechanistic insight into the disruption of photosynthesis regulation by metal/metalloids and highlights adaptive approaches to ameliorate their effects on plants. Focus was made on photostasis, nutrient interactions, phytohormones, and genetic interventions for mitigating metal/metalloid stresses.

Proteome Landscape during Ripening of Solid Endosperm from Two Different Coconut Cultivars Reveals Contrasting Carbohydrate and Fatty Acid Metabolic Pathway Modulation

Cocos nucifera L. is a crop grown in the humid tropics. It is grouped into two classes of varieties: dwarf and tall; regardless of the variety, the endosperm of the coconut accumulates carbohydrates in the early stages of maturation and fatty acids in the later stages, although the biochemical factors that determine such behavior remain unknown. We used tandem mass tagging with synchronous precursor selection (TMT-SPS-MS3) to analyze the proteomes of solid endosperms from Yucatan green dwarf (YGD) and Mexican pacific tall (MPT) coconut cultivars. The analysis was conducted at immature, intermediate, and mature development stages to better understand the regulation of carbohydrate and lipid metabolisms. Proteomic analyses showed 244 proteins in YGD and 347 in MPT; from these, 155 proteins were shared between both cultivars. Furthermore, the proteomes related to glycolysis, photosynthesis, and gluconeogenesis, and those associated with the biosynthesis and elongation of fatty acids, were up-accumulated in the solid endosperm of MPT, while in YGD, they were down-accumulated. These results support that carbohydrate and fatty acid metabolisms differ among the developmental stages of the solid endosperm and between the dwarf and tall cultivars. This is the first proteomics study comparing different stages of maturity in two contrasting coconut cultivars and may help in understanding the maturity process in other palms.

A chloroplast diacylglycerol lipase modulates glycerolipid pathway balance in Arabidopsis

Two parallel pathways compartmentalized in the chloroplast and the endoplasmic reticulum contribute to thylakoid lipid synthesis in plants, but how these two pathways are coordinated during thylakoid biogenesis and remodeling remains unknown. We report here the molecular characterization of a homologous ADIPOSE TRIGLYCERIDE LIPASE-LIKE gene, previously referred to as ATGLL. The ATGLL gene is ubiquitously expressed throughout development and rapidly upregulated in response to a wide range of environmental cues. We show that ATGLL is a chloroplast non-regioselective lipase with a hydrolytic activity preferentially towards 16:0 of diacylglycerol (DAG). Comprehensive lipid profiling and radiotracer labeling studies revealed a negative correlation of ATGLL expression and the relative contribution of the chloroplast lipid pathway to thylakoid lipid biosynthesis. Additionally, we show that genetic manipulation of ATGLL expression resulted in changes in triacylglycerol levels in leaves. We propose that ATGLL, through affecting the level of prokaryotic DAG in the chloroplast, plays important roles in balancing the two glycerolipid pathways and in maintaining lipid homeostasis in plants.

Biosynthesis of Chlorophyll and Other Isoprenoids in the Plastid of Red Grape Berry Skins

Despite current knowledge showing that fruits like tomato and grape berries accumulate different components of the light reactions and Calvin cycle, the role of green tissues in fruits is not yet fully understood. In mature tomato fruits, chlorophylls are degraded and replaced by carotenoids through the conversion of chloroplasts in chromoplasts, while in red grape berries, chloroplasts persist at maturity and chlorophylls are masked by anthocyanins. To study isoprenoid and lipid metabolism in grape skin chloroplasts, metabolites of enriched organelle fractions were analyzed by high-performance liquid chromatography-high-resolution mass spectrometry (HPLC-HRMS) and the expression of key genes was evaluated by real-time polymerase chain reaction (PCR) in berry skins and leaves. Overall, the results indicated that chloroplasts of the grape berry skins, as with leaf chloroplasts, share conserved mechanisms of synthesis (and degradation) of important components of the photosynthetic machinery. Some of these components, such as chlorophylls and their precursors, and catabolites, carotenoids, quinones, and lipids have important roles in grape and wine sensory characteristics.

Physiological responses induced by phospholipase C isoform 5 upon heat stress in Arabidopsis thaliana

Plant's perception of heat stress involves several pathways and signaling molecules, such as phosphoinositide, which is derived from structural membrane lipids phosphatidylinositol. Phospholipase C (PLC) is a well-known signaling enzyme containing many isoforms in different organisms. In the present study, Phospholipase C Isoform 5 (PLC5) was investigated for its role in thermotolerance in Arabidopsis thaliana. Two over-expressing lines and one knock-down mutant of PLC5 were first treated at a moderate temperature (37 °C) and left for recovery. Then again exposed to a high temperature (45 °C) to check the seedling viability and chlorophyll contents. Root behavior and changes in ³²P_i labeled phospholipids were investigated after their exposure to high temperatures. Over-expression of PLC5 (PLC5 OE) exhibited quick and better phenotypic recovery with bigger and greener leaves followed by chlorophyll contents as compared to wild-type (Col-0) and PLC5 knock-down mutant in which seedling recovery was compromised. PLC5 knock-down mutant illustrated well-developed root architecture under controlled conditions but stunted secondary roots under heat stress as compared to over-expressing PLC5 lines. Around 2.3-fold increase in phosphatidylinositol 4,5-bisphosphate level was observed in PLC5 OE lines upon heat stress compared to wild-type and PLC5 knock-down mutant lines. A significant increase in phosphatidylglycerol was also observed in PLC5 OE lines as compared to Col-0 and PLC5 knock-down mutant lines. The results of the present study demonstrated that PLC5 over-expression contributes to heat stress tolerance while maintaining its photosynthetic activity and is also observed to be associated with primary and secondary root growth in Arabidopsis thaliana.

The influence of light microclimate on the lipid profile and associated transcripts of photosynthetically active grape berry seeds

Lipids and oils determine the quality and industrial value of grape seeds. Studies with legume seeds demonstrated the influence of light on lipid metabolism and its association with seed photosynthesis. Grape berry seeds are photosynthetically active till mature stage, but mostly during the green stage and veraison. The objective of this work was to compare the lipid profiles of seeds from white grape berries (cv. Alvarinho) growing at two contrasting light microclimates in the canopy (low and high light, LL and HL respectively), previously reported to have distinct photosynthetic competences. Berries were collected at three developmental stages (green, veraison and mature) and from both microclimates, and the seeds were analyzed for their lipid profiles in an untargeted manner using liquid chromatography coupled to high resolution mass spectrometry (LCMS). The seed lipid profiles differed greatly among berry developmental stages, and to a lesser extend between microclimates. The LL microclimate coincided with a higher relative levels of fatty acids specifically at mature stage, while the HL microclimate led to an up-regulation of ceramides at green stage and of triacylglycerols and glycerophospholipids at mature stage. The seed transcript levels of four key genes (VvACCase1, VvΔ9FAD, VvFAD6 and VvLOXO) involved in fatty acid metabolism were analyzed using real-time qPCR. The lipoxygenase gene (VvLOXO) was down- and up-regulated by HL, as compared to LL, in seeds at green and veraison stages, respectively. These results suggest that seed photosynthesis may play distinct roles during seed growth and development, possibly by fueling different lipid pathways: at green stage mainly towards the accumulation of membrane-bound lipid species that are essential for cell growth and maintenance of the photosynthetic machinery itself; and at veraison and mature stages mainly towards storage lipids that contribute to the final quality of the grape seeds.

Deacylation of galactolipids decomposes photosystem II dimers to enhance degradation of damaged D1 protein

Photosystem II (PSII) contains many lipid molecules that are essential for the function and maintenance of PSII. Under strong light conditions, PSII complexes are dynamically modified during the repair process; however, the molecular mechanism of the dynamic changes in the PSII structure is still unclear. In the present study, we investigated the role of a lipase in the repair of PSII in Synechocystis sp. PCC 6803. We identified a protein encoded by the sll1969 gene, previously named lipase A (lipA), in the Synechocystis sp. PCC 6803 genome as a candidate for the lipase involved in PSII repair. Recombinant protein expressed in Escherichia coli cells hydrolyzed fatty acids at the sn-1 position of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol as well as triacylglycerol esterified with stearic acids. PSII repair in a disrupted mutant of the lipA gene was suppressed by the slow degradation of damaged D1 protein under strong light. The level of the PSII dimer remained higher in lipA mutant cells than wild-type (WT) cells under strong light. LipA protein was associated with the PSII dimer in vivo, and recombinant LipA protein decomposed PSII dimers purified from WT cells to monomers by reducing MGDG content in the PSII complex. These results indicate that LipA reacts with PSII dimers, dissociates them into monomers by digesting MGDG, and enhances D1 degradation during PSII repair.

Insight into the regulatory networks underlying the high lipid perennial ryegrass growth under different irradiances

Under favourable conditions, perennial ryegrass (Lolium perenne) engineered to accumulated high lipid (HL) carbon sink in their leaves was previously shown to also enhance photosynthesis and growth. The greater aboveground biomass was found to be diminished in a dense canopy compared to spaced pots. Besides, the underlying genetic regulatory network linking between leaf lipid sinks and these physiological changes remains unknown. In this study, we demonstrated that the growth advantage was not displayed in HL Lolium grown in spaced pots under low lights. Under standard lights, analysis of differentiating transcripts in HL Lolium reveals that the plants had elevated transcripts involved in lipid metabolism, light capturing, photosynthesis, and sugar signalling while reduced expression of genes participating in sugar biosynthesis and transportation. The plants also had altered several transcripts involved in mitochondrial oxidative respiration and redox potential. Many of the above upregulated or downregulated transcript levels were found to be complemented by growing the plants under low light. Overall, this study emphasizes the importance of carbon and energy homeostatic regulatory mechanisms to overall productivity of the HL Lolium through photosynthesis, most of which are significantly impacted by low irradiances.

Effects of heat shock on photosynthesis-related characteristics and lipid profile of Cycas multipinnata and C. panzhihuaensis

BACKGROUND

Cycas multipinnata and C. panzhihuaensis are two attractive ornamental tree species. With the global climate change, the temperature in the natural habitats of both the species shows a marked rising trend. However, how the two species respond to extreme high temperatures are not clear. Chlorophyll fluorescence parameters, chlorophyll content, chloroplast ultrastructure and lipid metabolism in the two species were determined following plant exposure to heat stress.

RESULTS

The results demonstrated that the photosynthetic efficiency decreased significantly in both the species following heat shock and recovery, but to a greater extent in C. panzhihuaensis. Compared to the control, chlorophyll content of C. multipinnata did not change significantly following heat stress and recovery. However, chlorophyll content of C. panzhihuaensis increased significantly after 1 d of recovery in comparison with the control. Chloroplast ultrastructures of C. panzhihuaensis were more severely affected by heat shock than C. multipinnata. C. multipinnata and C. panzhihuaensis followed a similar change trend in the amounts of most of the lipid categories after heat stress. However, only the amounts of lysophospholipids and fatty acyls differed significantly between the two species following heat treatment. Additionally, the unsaturation levels of the major lipid classes in C. multipinnata were significantly lower than or equal to those in C. panzhihuaensis.

CONCLUSIONS

C. multipinnata was less affected by extremely high temperatures than C. panzhihuaensis. The differential stability of chlorophyll and chloroplast ultrastructure and the differential adjustment of lipid metabolism might contribute to the different responses to heat shock between the two species.

Light Intensity- and Spectrum-Dependent Redox Regulation of Plant Metabolism

Both light intensity and spectrum (280–800 nm) affect photosynthesis and, consequently, the formation of reactive oxygen species (ROS) during photosynthetic electron transport. ROS, together with antioxidants, determine the redox environment in tissues and cells, which in turn has a major role in the adjustment of metabolism to changes in environmental conditions. This process is very important since there are great spatial (latitude, altitude) and temporal (daily, seasonal) changes in light conditions which are accompanied by fluctuations in temperature, water supply, and biotic stresses. The blue and red spectral regimens are decisive in the regulation of metabolism because of the absorption maximums of chlorophylls and the sensitivity of photoreceptors. Based on recent publications, photoreceptor-controlled transcription factors such as ELONGATED HYPOCOTYL5 (HY5) and changes in the cellular redox environment may have a major role in the coordinated fine-tuning of metabolic processes during changes in light conditions. This review gives an overview of the current knowledge of the light-associated redox control of basic metabolic pathways (carbon, nitrogen, amino acid, sulphur, lipid, and nucleic acid metabolism), secondary metabolism (terpenoids, flavonoids, and alkaloids), and related molecular mechanisms. Light condition-related reprogramming of metabolism is the basis for proper growth and development of plants; therefore, its better understanding can contribute to more efficient crop production in the future.

Transcriptional regulation of triacylglycerol accumulation in plants under environmental stress conditions

Triacylglycerol (TAG), a major energy reserve in lipid form, accumulates mainly in seeds. Although TAG concentrations are usually low in vegetative tissues because of the repression of seed maturation programs, these programs are derepressed upon the exposure of vegetative tissues to environmental stresses. Metabolic reprogramming of TAG accumulation is driven primarily by transcriptional regulation. A substantial proportion of transcription factors regulating seed TAG biosynthesis also participates in stress-induced TAG accumulation in vegetative tissues. TAG accumulation leads to the formation of lipid droplets and plastoglobules, which play important roles in plant tolerance to environmental stresses. Toxic lipid intermediates generated from environmental-stress-induced lipid membrane degradation are captured by TAG-containing lipid droplets and plastoglobules. This review summarizes recent advances in the transcriptional control of metabolic reprogramming underlying stress-induced TAG accumulation, and provides biological insight into the plant adaptive strategy, linking TAG biosynthesis with plant survival.

Chloroplast Lipids Metabolism and Function. A Redox Perspective

Plant productivity is determined by the conversion of solar energy into biomass through oxygenic photosynthesis, a process performed by protein-cofactor complexes including photosystems (PS) II and I, and ATP synthase. These complexes are embedded in chloroplast thylakoid membrane lipids, which thus function as structural support of the photosynthetic machinery and provide the lipid matrix to avoid free ion diffusion. The lipid and fatty acid composition of thylakoid membranes are unique in chloroplasts and cyanobacteria, which implies that these molecules are specifically required in oxygenic photosynthesis. Indeed, there is extensive evidence supporting a relevant function of glycerolipids in chloroplast biogenesis and photosynthetic efficiency in response to environmental stimuli, such as light and temperature. The rapid acclimation of higher plants to environmental changes is largely based on thiol-based redox regulation and the disulphide reductase activity thioredoxins (Trxs), which are reduced by ferredoxin (Fdx) via an Fdx-dependent Trx reductase. In addition, chloroplasts harbour an NADPH-dependent Trx reductase C, which allows the use of NADPH to maintain the redox homeostasis of the organelle. Here, we summarise the current knowledge of chloroplast lipid metabolism and the function of these molecules as structural basis of the complex membrane network of the organelle. Furthermore, we discuss evidence supporting the relevant role of lipids in chloroplast biogenesis and photosynthetic performance in response to environmental cues in which the redox state of the organelle plays a relevant role.

Mechanisms and functions of membrane lipid remodeling in plants

Lipid remodeling, defined herein as post-synthetic structural modifications of membrane lipids, play crucial roles in regulating the physicochemical properties of cellular membranes and hence their many functions. Processes affected by lipid remodeling include lipid metabolism, membrane repair, cellular homeostasis, fatty acid trafficking, cellular signaling and stress tolerance. Glycerolipids are the major structural components of cellular membranes and their composition can be adjusted by modifying their head groups, their acyl chain lengths and the number and position of double bonds. This review summarizes recent advances in our understanding of mechanisms of membrane lipid remodeling with emphasis on the lipases and acyltransferases involved in the modification of phosphatidylcholine and monogalactosyldiacylglycerol, the major membrane lipids of extraplastidic and photosynthetic membranes, respectively. We also discuss the role of triacylglycerol metabolism in membrane acyl chain remodeling. Finally, we discuss emerging data concerning the functional roles of glycerolipid remodeling in plant stress responses. Illustrating the molecular basis of lipid remodeling may lead to novel strategies for crop improvement and other biotechnological applications such as bioenergy production.