Glyoxylic acid overcomes 1-MCP-induced blockage of fruit ripening in Pyrus communis L. var. 'D'Anjou'

Arbuscular mycorrhiza differentially adjusts central carbon metabolism in two contrasting genotypes of Vigna radiata (L.) Wilczek in response to salt stress

The study aimed at investigating Arbuscular Mycorrhiza (AM) mediated metabolic changes in two genotypes of mungbean (Vigna radiata) differing in their salt tolerance in presence of salt stress (100 mM NaCl). Colonisation by Claroideoglomus etunicatum resulted in higher growth, photosynthetic efficiency, total protein content, and lower levels of stress markers, indicating alleviation of stress in mungbean plants. AM differentially upregulated the components of Tricarboxylic acid (TCA) cycle in salt tolerant (ST) and salt sensitive (SS) genotypes that could be correlated to AM-mediated moderation in nutrient uptake. Under salt stress, while maximum increase in the activity of α-ketoglutarate dehydrogenase (65%) was observed in mycorrhizal (M)-ST; the increase in isocitrate dehydrogenase (79%) and fumarase (133%) activities was maximum in M-SS plants over their non-mycorrhizal (NM) counterparts. Apart from TCA, AM also affected gamma-aminobutyric acid (GABA) and glyoxylate pathways. Activities of enzymes implicated in GABA shunt increased in both the genotypes under stress resulting in increase in GABA concentration (46%). Notably, glyoxylate pathway was induced by AM in SS only, wherein M-SS exhibited significantly higher isocitrate lyase (49%) and malate synthase (104%) activities, reflected in higher malic acid concentration (84%), than NM under stress. The results suggest that AM moderates the central carbon metabolism and strategizes towards boosting the formation of stress-alleviating metabolites such as GABA and malic acid, especially in SS, bypassing the steps catalysed by salt-sensitive enzymes in TCA cycle. The study, therefore, advances the understanding on mechanisms by which AM ameliorates salt stress.

Impact of heat stress, water stress, and their combined effects on the metabolism and transcriptome of grape berries

Recurring heat and drought episodes present challenges to the sustainability of grape production worldwide. We investigated the impacts of heat and drought stress on transcriptomic and metabolic responses of berries from two wine grape varieties. Cabernet Sauvignon and Riesling grapevines were subjected to one of four treatments during early fruit ripening: (1) drought stress only, (2) heat stress only, (3) simultaneous drought and heat stress, (4) no drought or heat stress (control). Berry metabolites, especially organic acids, were analyzed, and time-course transcriptome analysis was performed on samples before, during, and after the stress episode. Both alone and in conjunction with water stress, heat stress had a much more significant impact on berry organic acid content, pH, and titratable acidity than water stress. This observation contrasts with previous reports for leaves, which responded more strongly to water stress, indicating that grape berries display a distinct, organ-specific response to environmental stresses. Consistent with the metabolic changes, the global transcriptomic analysis revealed that heat stress had a more significant impact on gene expression in grape berries than water stress in both varieties. The differentially expressed genes were those associated with the tricarboxylic acid cycle and glyoxylate cycle, mitochondrial electron transport and alternative respiration, glycolysis and gluconeogenesis, carbohydrate allocation, ascorbate metabolism, and abiotic stress signaling pathways. Knowledge regarding how environmental stresses, alone and in combination, impact the berry metabolism of different grape varieties will form the basis for developing recommendations for climate change mitigation strategies and genetic improvement.

Analysis of the Fruit Quality of Pear (Pyrus spp.) Using Widely Targeted Metabolomics

Pear is a kind of common temperate fruit, whose metabolite composition that contributes to the difference in fruit quality is unclear. This study identified and quantified the metabolites using a widely targeted LC-MS/MS approach in three pear species, including Pyrus bretschneideri (PB), Pyrus usssuriensis (PU) and Pyrus pyrifolia (PP). A total of 493 metabolites were identified, consisting of 68 carbohydrates, 47 organic acids, 50 polyphenols, 21 amino acids, 20 vitamins, etc. The results of PCA and OPLS-DA demonstrated that the metabolite compositions differed distinctly with cultivar variability. Our results also involved some metabolic pathways that may link to the fruit quality based on KEGG pathway analysis, the pathway of phenylalanine metabolism revealed significant differences between PB and PP (p < 0.05). Furthermore, the study selected D-xylose, formononetin, procyanidin A1 and β-nicotinamide mononucleotide as the major differentially expressed metabolites in the three species. The present study can open new avenues for explaining the differences in fruit quality of the major commercial pear cultivars in China.

Transcriptome Analysis Reveals Potential Mechanisms for Ethylene-Inducible Pedicel–Fruit Abscission Zone Activation in Non-Climacteric Sweet Cherry (Prunus avium L.)

The harvesting of sweet cherry (Prunus avium L.) fruit is a labor-intensive process. The mechanical harvesting of sweet cherry fruit is feasible; however, it is dependent on the formation of an abscission zone at the fruit–pedicel junction. The natural propensity for pedicel—fruit abscission zone (PFAZ) activation varies by cultivar, and the general molecular basis for PFAZ activation is not well characterized. In this study, ethylene-inducible change in pedicel fruit retention force (PFRF) was recorded in a developmental time-course with a concomitant analysis of the PFAZ transcriptome from three sweet cherry cultivars. In ‘Skeena’, mean PFRF for both control and treatment fruit dropped below the 0.40 kg-force (3.92 N) threshold for mechanical harvesting, indicating the activation of a discrete PFAZ. In ‘Bing’, mean PFRF for both control and treatment groups decreased over time. However, a mean PFRF conducive to mechanical harvesting was achieved only in the ethylene-treated fruit. While in ‘Chelan’ the mean PFRF of the control and treatment groups did not meet the threshold required for efficient mechanical harvesting. Transcriptome analysis of the PFAZ region followed by the functional annotation, differential expression analysis, and gene ontology (GO) enrichment analyses of the data facilitated the identification of phytohormone-responsive and abscission-related transcripts, as well as processes that exhibited differential expression and enrichment in a cultivar-dependent manner over the developmental time-course. Additionally, read alignment-based variant calling revealed several short variants in differentially expressed genes, associated with enriched gene ontologies and associated metabolic processes, lending potential insight into the genetic basis for different abscission responses between the cultivars. These results provide genetic targets for the induction or inhibition of PFAZ activation, depending on the desire to harvest the fruit with or without the stem attached. Understanding the genetic mechanisms underlying the development of the PFAZ will inform future cultivar development while laying a foundation for mechanized sweet cherry harvest.

Aconitase: To Be or not to Be Inside Plant Glyoxysomes, That Is the Question

After the discovery in 1967 of plant glyoxysomes, aconitase, one the five enzymes involved in the glyoxylate cycle, was thought to be present in the organelles, and although this was found not to be the case around 25 years ago, it is still suggested in some textbooks and recent scientific articles. Genetic research (including the study of mutants and transcriptomic analysis) is becoming increasingly important in plant biology, so metabolic pathways must be presented correctly to avoid misinterpretation and the dissemination of bad science. The focus of our study is therefore aconitase, from its first localization inside the glyoxysomes to its relocation. We also examine data concerning the role of the enzyme malate dehydrogenase in the glyoxylate cycle and data of the expression of aconitase genes in Arabidopsis and other selected higher plants. We then propose a new model concerning the interaction between glyoxysomes, mitochondria and cytosol in cotyledons or endosperm during the germination of oil-rich seeds.