Nitrogen Deprivation-Induced Production of Volatile Organic Compounds in the Arachidonic-Acid-Accumulating Microalga Lobosphaera incisa Underpins Their Role as ROS Scavengers and Chemical Messengers

Funding Information: PK and AC acknowledged the Blaustein Postdoctoral Fellowship from the Blaustein Center for Scientific Cooperation (BGU). We are grateful to Noga Sikron Peres for her help with the GC-MS analysis. VT was the chair of Sonnenfeldt-Goldman Career Development in Desert Research. Funding. This work was supported by a grant from the Ministry of Science, Technology and Space, Israel (grant number 3-12422).Peer reviewedPublisher PD

Oil Pollution Affects the Central Metabolism of Keystone Vachellia (Acacia) Trees

Vachellia (formerly Acacia) trees are native to arid environments in Africa and the Arabian Peninsula, where they often support the local animal and plant communities acting as keystone species. The aim of this study was to examine whether oil pollution affected the central metabolism of the native keystone trees Vachellia tortilis (Forssk.) and V. raddiana (Savi), as either adults or seedlings. The study was conducted in the Evrona Nature Reserve, a desert ecosystem in southern Israel where two major oil spills occurred in 1975 and in 2014. Leaf samples were collected to analyze the central metabolite profiles from oil-polluted and unpolluted adult trees and from Vachellia seedlings growing in oil-polluted and unpolluted soils in an outdoor setup. We found that oil pollution had a stronger effect on one-year-old seedlings than on adult trees, reducing the levels of amino acids, sugars, and organic acids. While adult trees are mildly affected by oil pollution, the effects on young seedlings can cause a long-term reduction in the population of these keystone desert trees, ultimately threatening this entire ecosystem.The research was part of a postcontamination monitoring program in the Evrona Nature Reserve, funded by the Israel Nature and Parks Authority (INPA) and managed by the HaMaaragIsrael National Nature Assessment Program. We are grateful for the ongoing support to the ADSSC (Winters G.) by the Israel Ministry for Science and Technology (MOST). M.F. was the recipient of a postdoctoral fellowship from the Jacob Blaustein Center for Scientific Cooperation.info:eu-repo/semantics/publishedVersio

Integrated metabolomics identifies CYP72A67 and CYP72A68 oxidases in the biosynthesis of Medicago truncatula oleanate sapogenins

Introduction: Triterpene saponins are important bioactive plant natural products found in many plant families including the Leguminosae. Objectives: We characterize two Medicago truncatula cytochrome P450 enzymes, MtCYP72A67 and MtCYP72A68, involved in saponin biosynthesis including both in vitro and in planta evidence. Methods: UHPLC-(-)ESI-QToF-MS was used to profile saponin accumulation across a collection of 106 M. truncatula ecotypes. The profiling results identified numerous ecotypes with high and low saponin accumulation in root and aerial tissues. Four ecotypes with significant differential saponin content in the root and/or aerial tissues were selected, and correlated gene expression profiling was performed. Results: Correlation analyses between gene expression and saponin accumulation revealed high correlations between saponin content with gene expression of -amyrin synthase, MtCYP716A12, and two cytochromes P450 genes, MtCYP72A67 and MtCYP72A68. In vivo and in vitro biochemical assays using yeast microsomes containing MtCYP72A67 revealed hydroxylase activity for carbon 2 of oleanolic acid and hederagenin. This finding was supported by functional characterization of MtCYP72A67 using RNAi-mediated gene silencing in M. truncatula hairy roots, which revealed a significant reduction of 2-hydroxylated sapogenins. In vivo and in vitro assays with MtCYP72A68 produced in yeast showed multifunctional oxidase activity for carbon 23 of oleanolic acid and hederagenin. These findings were supported by overexpression of MtCYP72A68 in M. truncatula hairy roots, which revealed significant increases of oleanolic acid, 2-hydroxyoleanolic acid, hederagenin and total saponin levels. Conclusions: The cumulative data support that MtCYP72A68 is a multisubstrate, multifunctional oxidase and MtCYP72A67 is a 2-hydroxylase, both of which function during the early steps of triterpene-oleanate sapogenin biosynthesis

Dynamic Maize Responses to Aphid Feeding Are Revealed by a Time Series of Transcriptomic and Metabolomic Assays

As a response to insect attack, maize (Zea mays) has inducible defenses that involve large changes in gene expression and metabolism. Piercing/sucking insects such as corn leaf aphid (Rhopalosiphum maidis) cause direct damage by acquiring phloem nutrients as well as indirect damage through the transmission of plant viruses. To elucidate the metabolic processes and gene expression changes involved in maize responses to aphid attack, leaves of inbred line B73 were infested with corn leaf aphids for 2 to 96 h. Analysis of infested maize leaves showed two distinct response phases, with the most significant transcriptional and metabolic changes occurring in the first few hours after the initiation of aphid feeding. After 4 d, both gene expression and metabolite profiles of aphid-infested maize reverted to being more similar to those of control plants. Although there was a predominant effect of salicylic acid regulation, gene expression changes also indicated prolonged induction of oxylipins, although not necessarily jasmonic acid, in aphid-infested maize. The role of specific metabolic pathways was confirmed using Dissociator transposon insertions in maize inbred line W22. Mutations in three benzoxazinoid biosynthesis genes, Bx1, Bx2, and Bx6, increased aphid reproduction. In contrast, progeny production was greatly decreased by a transposon insertion in the single W22 homolog of the previously uncharacterized B73 terpene synthases TPS2 and TPS3. Together, these results show that maize leaves shift to implementation of physical and chemical defenses within hours after the initiation of aphid feeding and that the production of specific metabolites can have major effects in maize-aphid interactions.Peer reviewe

Cereal aphids differently affect benzoxazinoid levels in durum wheat.

Aphids are major pests in cereal crops that cause direct and indirect damage leading to yield reduction. Despite the fact that wheat provides 20% of the world's caloric and protein diet, its metabolic responses to aphid attack, in general, and specifically its production of benzoxazinoid defense compounds are poorly understood. The objective of this study was to compare the metabolic diversity of durum wheat seedlings (Triticum turgidum ssp. durum) under attack by three different cereal aphids: i) the English grain aphid (Sitobion avenae Fabricius), ii) the bird cherry-oat aphid (Rhopalosiphum padi L.), and iii) the greenbug aphid (Schizaphis graminum Rondani), which are some of the most destructive aphid species to wheat. Insect progeny bioassays and metabolic analyses using chromatography/Q-Exactive/mass spectrometry non-targeted metabolomics and a targeted benzoxazinoid profile were performed on infested leaves. The insect bioassays revealed that the plants were susceptible to S. graminum, resistant to S. avenae, and mildly resistant to R. padi. The metabolic analyses of benzoxazinoids suggested that the predominant metabolites DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin- 3-one) and its glycosylated form DIMBOA-glucoside (Glc) were significantly induced upon both S. avenae, and R. padi aphid feeding. However, the levels of the benzoxazinoid metabolite HDMBOA-Glc (2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside) were enhanced due to the feeding of S. avenae and S. graminum aphids, to which Svevo was the most resistant and the most susceptible, respectively. The results showed a partial correlation between the induction of benzoxazinoids and aphid reproduction. Overall, our observations revealed diverse metabolic responses of wheat seedlings to cereal aphid feeding

Coordinated Gene Networks Regulating Arabidopsis Plant Metabolism in Response to Various Stresses and Nutritional Cues[W]

This work introduces a bioinformatics approach that identifies positive and negative coordination of gene expression between sets of genes, or entire gene networks, in response to environmental or developmental cues. The approach is illustrated by a case study that identifies distinct expression behavior of the energy-associated gene network in response to different biotic and abiotic stresses

A role for 9-lipoxygenases in maize defense against insect herbivory

<p>Feeding by <i>Spodoptera exigua</i> (beet armyworm) larvae on <i>Zea mays</i> (maize) induces expression of 9-lipoxygenases to a greater extent than 13-lipoxygenases. Whereas 13-lipoxygenases have an established role in the synthesis of jasmonates that serve as defense signaling molecules in many plant species, relatively little is known about the role of 9-lipoxygenases in herbivore defense. Phylogenetic analysis of lipoxygenases from maize inbred lines B73 and W22 shows that, although most <i>Lox</i> genes are present in both lines, <i>Lox12</i>, a 9-lipoxygenase that has been implicated in fungal defense, is truncated and unlikely to encode a functional protein in W22. Two independent <i>Mutator</i> transposon insertions in another 9-lipoxygenase, <i>Lox4</i>, caused improved <i>S. exigua</i> growth on the mutant lines relative to wildtype W22. This observation suggests a function in herbivore defense for metabolic products downstream of maize Lox4, either through direct toxicity or a perhaps an as yet unknown signaling function.</p

A friend in need is a friend indeed: Understanding stress-associated transcriptional networks of plant metabolism using cliques of coordinately expressed genes

The response of plants to environmental cues, particularly stresses, involves the coordinated induction or repression of gene expression. In a previous study, we developed a bioinformatics approach to analyze the mutual expression pattern of genes encoding transcription factors and metabolic enzymes upon exposure of Arabidopsis plants to abiotic and biotic stresses. The analysis resulted in three gene clusters, each displaying a unique expression pattern. In this article, we address the composition of each of these three clusters in regard to the functional identity of their encoded proteins as enzymes or transcription factors