Belowground ABA boosts aboveground production of DIMBOA and primes induction of chlorogenic acid in maize

Induced biosynthesis of chlorogenic acid in sweetpotato leaves confers the resistance against sweetpotato weevil attack

Sweetpotato weevil is among the most harmful pests in some major sweetpotato growing areas with warm climates. To enable the future establishment of safe weevil-resistance strategies, anti-weevil metabolites from sweetpotato should be investigated. In the present study, we pretreated sweetpotato leaves with exogenous chlorogenic acid and then exposed them to sweetpotato weevils to evaluate this compound's anti-insect activity. We found that chlorogenic acid applied to sweetpotato conferred significant resistance against sweetpotato-weevil feeding. We also observed enhanced levels of chlorogenic acid in response to weevil attack in sweetpotato leaves. To clarify how sweetpotato weevils regulate the generation of chlorogenic acid, we examined key elements of plant-herbivore interaction: continuous wounding and phytohormones participating in chlorogenic acid formation. According to our results, sweetpotato weevil-derived continuous wounding induces increases in phytohormones, including jasmonic acid, salicylic acid, and abscisic acid. These phytohormones can upregulate expression levels of genes involved in chlorogenic acid formation, such as IbPAL, IbC4H and IbHQT, thereby leading to enhanced chlorogenic acid generation. This information should contribute to understanding of the occurrence and formation of natural anti-weevil metabolites in sweetpotato in response to insect attack and provides critical targets for the future breeding of anti-weevil sweetpotato cultivars.

Transcriptome profiling of the Australian arid-land plant Eremophila serrulata (A.DC.) Druce (Scrophulariaceae) for the identification of monoterpene synthases

Plant terpenoids are a large and highly diverse class of metabolites with an important role in the immune defense. They find wide industrial application as active pharmaceutical ingredients, aroma and fragrance compounds. Several Eremophila sp. derived terpenoids have been documented. To elucidate the terpenoid metabolism, the transcriptome of juvenile and mature Eremophila serrulata (A.DC.) Druce (Scrophulariaceae) leaves was sequenced and a transcript library was generated. We report on the first transcriptomic dataset of an Eremophila plant. IlluminaMiSeq sequencing (2 × 300 bp) revealed 7,093,266 paired reads, which could be assembled to 34,505 isogroups. To enable detection of terpene biosynthetic genes, leaves were separately treated with methyl jasmonate, a well-documented inducer of plant secondary metabolites. In total, 21 putative terpene synthase genes were detected in the transcriptome data. Two terpene synthase isoenzymatic genes, termed ES01 and ES02, were successfully expressed in E. coli. The resulting proteins catalyzed the conversion of geranyl pyrophosphate, the universal substrate of monoterpene synthases to myrcene and Z-(b)-ocimene, respectively. The transcriptomic data and the discovery of the first terpene synthases from Eremophila serrulata are the initial step for the understanding of the terpene metabolism in this medicinally important plant genus.

Biochemical analysis of 'kerosene tree' Hymenaea courbaril L. under heat stress

Hymenaea courbaril or jatoba is a tropical tree known for its medically important secondary metabolites production. Considering climate change, the goal of this study was to investigate differential expression of proteins and lipids produced by this tree under heat stress conditions. Total lipid was extracted from heat stressed plant leaves and various sesquiterpenes produced by the tree under heat stress were identified. Gas chromatographic and mass spectrometric analysis were used to study lipid and volatile compounds produced by the plant. Several volatiles, isoprene, 2-methyl butanenitrile, β ocimene and a numbers of sesquiterpenes differentially produced by the plant under heat stress were identified. We propose these compounds were produced by the tree to cope up with heat stress. A protein gel electrophoresis (2-D DIGE) was performed to study differential expression of proteins in heat stressed plants. Several proteins were found to be expressed many folds different in heat stressed plants compared to the control. These proteins included heat shock proteins, histone proteins, oxygen evolving complex, and photosynthetic proteins, which, we believe, played key roles in imparting thermotolerance in Hymenaea tree. To the best of our knowledge, this is the first report of extensive molecular physiological study of Hymenaea trees under heat stress. This work will open avenues of further research on effects of heat stress in Hymenaea and the findings can be applied to understand how global warming can affect physiology of other plants.

Metabolomics of cereals under biotic stress: current knowledge and techniques

Prone to attacks by pathogens and pests, plants employ intricate chemical defense mechanisms consisting of metabolic adaptations. However, many plant attackers are manipulating the host metabolism to counteract defense responses and to induce favorable nutritional conditions. Advances in analytical chemistry have allowed the generation of extensive metabolic profiles during plant-pathogen and pest interactions. Thereby, metabolic processes were found to be highly specific for given tissues, species, and plant-pathogen/pest interactions. The clusters of identified compounds not only serve as base in the quest of novel defense compounds, but also as markers for the characterization of the plants' defensive state. The latter is especially useful in agronomic applications where meaningful markers are essential for crop protection. Cereals such as maize make use of their metabolic arsenal during both local and systemic defense responses, and the chemical response is highly adapted to specific attackers. Here, we summarize highlights and recent findings of metabolic patterns of cereals under pathogen and pest attack.

Costs of jasmonic acid induced defense in aboveground and belowground parts of corn (Zea mays L.)

Costs of jasmonic acid (JA) induced plant defense have gained increasing attention. In this study, JA was applied continuously to the aboveground (AG) or belowground (BG) parts, or AG plus BG parts of corn (Zea mays L.) to investigate whether JA exposure in one part of the plant would affect defense responses in another part, and whether or not JA induced defense would incur allocation costs. The results indicated that continuous JA application to AG parts systemically affected the quantities of defense chemicals in the roots, and vice versa. Quantities of DIMBOA and total amounts of phenolic compounds in leaves or roots generally increased 2 or 4 wk after the JA treatment to different plant parts. In the first 2 wk after application, the increase of defense chemicals in leaves and roots was accompanied by a significant decrease of root length, root surface area, and root biomass. Four weeks after the JA application, however, no such costs for the increase of defense chemicals in leaves and roots were detected. Instead, shoot biomass and root biomass increased. The results suggest that JA as a defense signal can be transferred from AG parts to BG parts of corn, and vice versa. Costs for induced defense elicited by continuous JA application were found in the early 2 wk, while distinct benefits were observed later, i.e., 4 wk after JA treatment.

Genetic variation and evolution of secondary compounds in native and introduced populations of the invasive plant Melaleuca quinquenervia

We examined multivariate evolution of 20 leaf terpenoids in the invasive plant Melaleuca quinquenervia in a common garden experiment. Although most compounds, including 1,8-Cineole and Viridiflorol, were reduced in home compared with invaded range genotypes, consistent with an evolutionary decrease in defense, one compound (E-Nerolidol) was greater in invaded than home range genotypes. Nerolidol was negatively genetically correlated with Cineole and Viridiflorol, and the increase in this compound in the new range may have been driven by this negative correlation. There was positive selection on all three focal compounds, and a loss of genetic variation in introduced range genotypes. Selection skewers analysis predicted an increase in Cineole and Viridiflorol and a decrease or no change in Nerolidol, in direct contrast to the observed changes in the new range. This discrepancy could be due to differences in patterns of selection, genetic correlations, or the herbivore communities in the home versus introduced ranges. Although evolutionary changes in most compounds were consistent with the evolution of increased competitive ability hypothesis, changes in other compounds as well as selection patterns were not, indicating that it is important to understand selection and the nature of genetic correlations to predict evolutionary change in invasive species.

Aboveground to belowground herbivore defense signaling in maize: a two-way street?

Insect pests that attempt to feed on the caterpillar-resistant maize genotype Mp708 encounter a potent, multipronged defense system that thwarts their invasion. First, these plants are on "constant alert" due to constitutively elevated levels of the phytohormone jasmonic acid that signals the plant to activate its defenses. The higher jasmonic acid levels trigger the expression of defense genes prior to herbivore attack so the plants are "primed" and respond with a faster and stronger defense. The second defense is the rapid accumulation of a toxic cysteine protease called Mir1-CP in the maize whorl in response to caterpillar feeding. When caterpillars ingest Mir1-CP, it damages the insect's midgut and retards their growth. In this article, we discuss a third possible defense strategy employed by Mp708. We have shown that foliar caterpillar feeding causes Mir1-CP and defense gene transcripts to accumulate in its roots. We propose that caterpillar feeding aboveground sends a signal belowground via the phloem that results in Mir1-CP accumulation in the roots. We also postulate that the roots serve as a reservoir of Mir1-CP that can be mobilized to the whorl in response to caterpillar assault.