Myo-inositol biosynthesis genes in Arabidopsis: differential patterns of gene expression and role in cell death

L-Ascorbic acid metabolism and regulation in fruit crops

L-Ascorbic acid (AsA) is more commonly known as vitamin C and is an indispensable compound for human health. As a major antioxidant, AsA not only maintains redox balance and resists biological and abiotic stress but also regulates plant growth, induces flowering, and delays senescence through complex signal transduction networks. However, AsA content varies greatly in horticultural crops, especially in fruit crops. The AsA content of the highest species is approximately 1,800 times higher than that of the lowest species. There have been significant advancements in the understanding of AsA accumulation in the past 20 years. The most noteworthy accomplishment was the identification of the critical rate-limiting genes for the 2 major AsA synthesis pathways (L-galactose pathway and D-galacturonic acid pathway) in fruit crops. The rate-limiting genes of the former are GMP, GME, GGP, and GPP, and the rate-limiting gene of the latter is GalUR. Moreover, APX, MDHAR, and DHAR are also regarded as key genes in degradation and regeneration pathways. Interestingly, some of these key genes are sensitive to environmental factors, such as GGP being induced by light. The efficiency of enhancing AsA content is high by editing upstream open reading frames (uORF) of the key genes and constructing multi-gene expression vectors. In summary, the AsA metabolism has been well understood in fruit crops, but the transport mechanism of AsA and the synergistic improvement of AsA and other traits is less known, which will be the focus of AsA research in fruit crops.

Exogenous Myo-Inositol Alleviates Salt Stress by Enhancing Antioxidants and Membrane Stability via the Upregulation of Stress Responsive Genes in Chenopodium quinoa L

Myo-inositol has gained a central position in plants due to its vital role in physiology and biochemistry. This experimental work assessed the effects of salinity stress and foliar application of myo-inositol (MYO) on growth, chlorophyll content, photosynthesis, antioxidant system, osmolyte accumulation, and gene expression in quinoa (Chenopodium quinoa L. var. Giza1). Our results show that salinity stress significantly decreased growth parameters such as plant height, fresh and dry weights of shoot and root, leaf area, number of leaves, chlorophyll content, net photosynthesis, stomatal conductance, transpiration, and Fv/Fm, with a more pronounced effect at higher NaCl concentrations. However, the exogenous application of MYO increased the growth and photosynthesis traits and alleviated the stress to a considerable extent. Salinity also significantly reduced the water potential and water use efficiency in plants under saline regime; however, exogenous application of myo-inositol coped with this issue. MYO significantly reduced the accumulation of hydrogen peroxide, superoxide, reduced lipid peroxidation, and electrolyte leakage concomitant with an increase in the membrane stability index. Exogenous application of MYO up-regulated the antioxidant enzymes' activities and the contents of ascorbate and glutathione, contributing to membrane stability and reduced oxidative damage. The damaging effects of salinity stress on quinoa were further mitigated by increased accumulation of osmolytes such as proline, glycine betaine, free amino acids, and soluble sugars in MYO-treated seedlings. The expression pattern of OSM34, NHX1, SOS1A, SOS1B, BADH, TIP2, NSY, and SDR genes increased significantly due to the application of MYO under both stressed and non-stressed conditions. Our results support the conclusion that exogenous MYO alleviates salt stress by involving antioxidants, enhancing plant growth attributes and membrane stability, and reducing oxidative damage to plants.

Metabolite Profiling in Arabidopsisthaliana with Moderately Impaired Photorespiration Reveals Novel Metabolic Links and Compensatory Mechanisms of Photorespiration

Photorespiration is an integral component of plant primary metabolism. Accordingly, it has been often observed that impairing the photorespiratory flux negatively impacts other cellular processes. In this study, the metabolic acclimation of the Arabidopsisthaliana wild type was compared with the hydroxypyruvate reductase 1 (HPR1; hpr1) mutant, displaying only a moderately reduced photorespiratory flux. Plants were analyzed during development and under varying photoperiods with a combination of non-targeted and targeted metabolome analysis, as well as ¹³C- and ¹⁴C-labeling approaches. The results showed that HPR1 deficiency is more critical for photorespiration during the vegetative compared to the regenerative growth phase. A shorter photoperiod seems to slowdown the photorespiratory metabolite conversion mostly at the glycerate kinase and glycine decarboxylase steps compared to long days. It is demonstrated that even a moderate impairment of photorespiration severely reduces the leaf-carbohydrate status and impacts on sulfur metabolism. Isotope labeling approaches revealed an increased CO₂ release from hpr1 leaves, most likely occurring from enhanced non-enzymatic 3-hydroxypyruvate decarboxylation and a higher flux from serine towards ethanolamine through serine decarboxylase. Collectively, the study provides evidence that the moderate hpr1 mutant is an excellent tool to unravel the underlying mechanisms governing the regulation of metabolic linkages of photorespiration with plant primary metabolism.

Spodoptera litura-mediated chemical defense is differentially modulated in older and younger systemic leaves of Solanum lycopersicum

Metabolite profiling, biochemical assays, and transcript analysis revealed differential modulation of specific induced defense responses in local, older, and younger systemic leaves in Solanum lycopersicum upon Spodoptera litura herbivory. Plants reconfigure their metabolome upon herbivory to induce production of defense metabolites involved in both direct and indirect defenses against insect herbivores. Herbivory mediated leaf-to-leaf systemic induction pattern of primary and non-volatile secondary metabolites is not well studied in tomato. Here, we show that, in cultivated tomato Solanum lycopersicum herbivory by generalist insect, Spodoptera litura results in differential alteration of primary metabolites, majorly sugars and amino acids and specific secondary metabolites in local, younger, and older systemic leaves. Cluster analysis of 55 metabolites identified by GC-MS showed correlation between local and younger systemic leaves. Re-allocation of primary metabolites like glucose and amino acids from the local to systemic leaf was observed. Secondary metabolites chlorogenic acid, caffeic acid, and catechin were significantly induced during herbivory in systemic leaves. Among specific secondary metabolites, chlorogenic acid and catechin significantly inhibits S. litura larval growth in all stages. Local leaf exhibited increased lignin accumulation upon herbivory. Differential alteration of induced defense responses like reactive oxygen species, polyphenol oxidase activity, proteinase inhibitor, cell wall metabolites, and lignin accumulation was observed in systemic leaves. The metabolite alteration also resulted in increased defense in systemic leaves. Thus, comparative analysis of metabolites in local and systemic leaves of tomato revealed a constant re-allocation of primary metabolites to systemic leaves and differential induction of secondary metabolites and induced defenses upon herbivory.

Galactinol synthase enzyme activity influences raffinose family oligosaccharides (RFO) accumulation in developing chickpea (Cicer arietinum L.) seeds

To understand raffinose family oligosaccharides (RFO) metabolism in chickpea (Cicer arietinum L.) seeds, RFO accumulation and corresponding biosynthetic enzymes activities were determined during seed development of chickpea genotypes with contrasting RFO concentrations. RFO concentration in mature seeds was found as a facilitator rather than a regulating step of seed germination. In mature seeds, raffinose concentrations ranged from 0.38 to 0.68 and 0.75 to 0.99 g/100 g, whereas stachyose concentrations varied from 0.79 to 1.26 and 1.70 to 1.87 g/100 g indicating significant differences between low and high RFO genotypes, respectively. Chickpea genotypes with high RFO concentration accumulated higher concentrations of myo-inositol and sucrose during early seed developmental stages suggesting that initial substrate concentrations may influence RFO concentration in mature seeds. High RFO genotypes showed about two to three-fold higher activity for all RFO biosynthetic enzymes compared to those with low RFO concentrations. RFO biosynthetic enzymes activities correspond with accumulation of individual RFO during seed development.

Phytate in pig and poultry nutrition

Phosphorus (P) is primarily stored in the form of phytates in plant seeds, thus being poorly available for monogastric livestock, such as pigs and poultry. As phytate is a polyanionic molecule, it has the capacity to chelate positively charged cations, especially calcium, iron and zinc. Furthermore, it probably compromises the utilization of other dietary nutrients, including protein, starch and lipids. Reduced efficiency of utilization implies both higher levels of supplementation and increased discharge of the undigested nutrients to the environment. The enzyme phytase catalyses the stepwise hydrolysis of phytate. In respect to livestock nutrition, there are four possible sources of this enzyme available for the animals: endogenous mucosal phytase, gut microfloral phytase, plant phytase and exogenous microbial phytase. As the endogenous mucosal phytase in monogastric organisms appears incapable of hydrolysing sufficient amounts of phytate-bound P, supplementation of exogenous microbial phytase in diets is a common method to increase mineral and nutrient absorption. Plant phytase activity varies greatly among species of plants, resulting in differing gastrointestinal phytate hydrolysis in monogastric animals. Besides the supplementation of microbial phytase, processing techniques are alternative approaches to reduce phytate contents. Thus, techniques such as germination, soaking and fermentation enable activation of naturally occurring plant phytase among others. However, further research is needed to tap the potential of these technologies. The main focus herein is to review the available literature on the role of phytate in pig and poultry nutrition, its degradation throughout the gut and opportunities to enhance the utilization of P as well as other minerals and nutrients which might be complexed by phytates.

Stress-related genes distinctly expressed in unfertilized wheat ovaries under both normal and water deficit conditions whereas differed in fertilized ovaries

In this study, a proteomic approach was utilized to identify differentially accumulated proteins in developing wheat ovaries before and after fertilization and in response to water deficit. Proteins were extracted, quantified, and resolved by 2-DE at pH4-7. Statistical analysis of spot intensity was performed by using principal component analysis and samples were clustered by using Euclidean distance. In total, 136 differentially accumulated protein spots representing 88 unique proteins were successfully identified by MALDI-TOF/TOF MS. Under normal conditions, stress-related proteins were abundant in unfertilized ovaries while proteins involved in the metabolism of energy and matter were enriched in fertilized ovaries just 48h after fertilization. Similar trends were observed in unfertilized and fertilized wheat ovaries under water deficit conditions, except for increased accumulation of stress-related proteins in fertilized ovaries. Some proteins required for normal development were not present in ovaries subjected to water deficit. Our comprehensive results provide new insights into the biochemical mechanisms involved in ovary development before and after fertilization and in tolerance to water deficit.

BIOLOGICAL SIGNIFICANCE

Fertilization initiates the most dramatic changes that occur in the life cycle of higher plants; research into differences in gene expression before and after ovary pollination can make a substantial contribution to understanding the physiological and biochemical processes associated with fertilization. To date, a small number of studies have examined changes in transcriptional activity of the developing plant embryo sac before and after fertilization. However, comparative proteomic analysis of wheat ovary development before and after fertilization, and in response to water deficit, has not yet been reported. Our comprehensive results provide new insights into the biochemical mechanisms involved in ovary development before and after fertilization and in tolerance to water deficit.

Changes in the metabolome and histopathology of Amaranthus hypochondriacus L. in response to Ageratum enation virus infection

Amaranthus hypochondriacus L. infected with Ageratum enation virus (AEV) was investigated for identifying alteration in the anatomical structures, sap translocation and metabolomic variations using light microscopy, magnetic resonance imaging, NMR spectroscopy and GC-MS, respectively. Combination of GC-MS and NMR spectroscopy identified 68 polar and non-polar metabolites that were present in different levels in healthy and virus-infected A. hypochondriacus. Contrast of T₁ and T₂ weighted MR images showed significant differences in the spatial distribution of water, lipids and macromolecules indicating alterations in the cortical region and disruption of vascular bundles in virus-infected stem tissues. MRI observations are supported by light microscopic examination. Microscopic examination of AEV infected stem revealed severe hyperplasia with a considerable reduction in size of stem cells. The NMR spectroscopy and GC-MS analysis indicated that viral infection significantly affected the plant primary and secondary metabolism resulting in decreased glucose and sucrose content and increase in the concentration of β-sitosterol and stigmasterol. Higher accumulation of TCA cycle intermediates such as citric acid and malic acid in AEV infected plants indicated enhanced rate of respiratory metabolism. The viral stress significantly increases the concentration of erythritol and myo-inositol as compared to healthy ones. Lower concentration of glucose and sucrose in viral-infected stem tissues suggests decreased translocation of photosynthates in the plants. The results demonstrated potential of MRI, NMR spectroscopy and GC-MS for studying anatomical and metabolic variations in virus-infected plants.