Plant Defense Compounds Research Articles

Hyperaccumulator Stanleya pinnata: In Situ Fitness in Relation to Tissue Selenium Concentration.

Earlier studies have shown that Stanleya pinnata benefits from selenium hyperaccumulation through ecological benefits and enhanced growth. However, no investigation has assayed the effects of Se hyperaccumulation on plant fitness in the field. This research aimed to analyze how variation in Se accumulation affects S. pinnata fitness, judged from physiological and biochemical performance parameters and herbivory while growing naturally on two seleniferous sites. Natural variation in Se concentration in vegetative and reproductive tissues was determined, and correlations were explored between Se levels with fitness parameters, herbivory damage, and plant defense compounds. Leaf Se concentration varied between 13- and 55-fold in the two populations, averaging 868 and 2482 mg kg−1 dry weight (DW). Furthermore, 83% and 31% of plants from the two populations showed Se hyperaccumulator levels in leaves (>1000 mg kg−1 DW). In seeds, the Se levels varied 3–4-fold and averaged 3372 and 2267 mg kg−1 DW, well above the hyperaccumulator threshold. Plant size and reproductive parameters were not correlated with Se concentration. There was significant herbivory pressure even on the highest-Se plants, likely from Se-resistant herbivores. We conclude that the variation in Se hyperaccumulation did not appear to enhance or compromise S. pinnata fitness in seleniferous habitats within the observed Se range.

Drought stress increases the expression of barley defence genes with negative consequences for infesting cereal aphids.

Crops are exposed to myriad abiotic and biotic stressors with negative consequences. Two stressors that are expected to increase under climate change are drought and infestation with herbivorous insects, including important aphid species. Expanding our understanding of the impact drought has on the plant-aphid relationship will become increasingly important under future climate scenarios. Here we use a previously characterized plant-aphid system comprising a susceptible variety of barley, a wild relative of barley with partial aphid resistance, and the bird cherry-oat aphid to examine the drought-plant-aphid relationship. We show that drought has a negative effect on plant physiology and aphid fitness, and provide evidence to suggest that plant resistance influences aphid responses to drought stress. Furthermore, we show that the expression of thionin genes, plant defensive compounds that contribute to aphid resistance, increase in susceptible plants exposed to drought stress but remain at constant levels in the partially resistant plant, suggesting that they play an important role in determining the success of aphid populations. This study highlights the role of plant defensive processes in mediating the interactions between the environment, plants, and herbivorous insects.

Possible roles of insoluble proanthocyanidin in Tartary buckwheat (Fagopyrum tataricum) leaves

AbstractInsoluble proanthocyanidins are reported as plant defence compounds against herbivorous insects. This is the first report to demonstrate the occurrence of insoluble proanthocyanidins in plants of the Polygonaceae family. In this study, we identified a mutant Tartary buckwheat (Fagopyrum tataricum) cultivar, ‘Hokkai T10’, that lacks insoluble proanthocyanidins accumulation in leaves and shows a role in defence against common cutworm (Spodoptera litura Fabricius). We did not detect insoluble proanthocyanidins in p‐dimethylaminocinnamaldehyde stain in ‘Hokkai T10’. The expression of the trait should be regulated by at least one recessive gene named iPA. The leaves of ‘Hokkai T10’ were ingested in larger amount by S. litura than the wild type. This fact supports the hypothesis that insoluble proanthocyanidins have a role in protection against insects. This is the first report to demonstrate a resistance role of insoluble proanthocyanidins using insect preference. In addition, the germination rate of ‘Hokkai T10’ was significantly higher than wild type; indicating to show firstly the effects of insoluble proanthocyanidins on seed germination.

Phenolic degradation by catechol dioxygenases is associated with pathogenic fungi with a necrotrophic lifestyle in the Ceratocystidaceae.

Fungal species of the Ceratocystidaceae grow on their host plants using a variety of different lifestyles, from saprophytic to highly pathogenic. Although many genomes of fungi in the Ceratocystidaceae are publicly available, it is not known how the genes that encode catechol dioxygenases (CDOs), enzymes involved in the degradation of phenolic plant defense compounds, differ among members of the Ceratocystidaceae. The aim of this study was therefore to identify and characterize the genes encoding CDOs in the genomes of Ceratocystidaceae representatives. We found that genes encoding CDOs are more abundant in pathogenic necrotrophic species of the Ceratocystidaceae and less abundant in saprophytic species. The loss of the CDO genes and the associated 3-oxoadipate catabolic pathway appears to have occurred in a lineage-specific manner. Taken together, this study revealed a positive association between CDO gene copy number and fungal lifestyle in Ceratocystidaceae representatives.

Sequestration of Plant Defense Compounds by Insects: From Mechanisms to Insect-Plant Coevolution.

Plant defense compounds play a key role in the evolution of insect-plant associations by selecting for behavioral, morphological, and physiological insect adaptations. Sequestration, the ability of herbivorous insects to accumulate plant defense compounds to gain a fitness advantage, represents a complex syndrome of adaptations that has evolved in all major lineages of herbivorous insects and involves various classes of plant defense compounds. In this article, we review progress in understanding how insects selectively accumulate plant defense metabolites and how the evolution of specific resistance mechanisms to these defense compounds enables sequestration. These mechanistic considerations are further integrated into the concept of insect-plant coevolution. Comparative genome and transcriptome analyses, combined with approaches based on analytical chemistry that are centered in phylogenetic frameworks, will help to reveal adaptations underlying the sequestration syndrome, which is essential to understanding the influence of sequestration on insect-plant coevolution.

Illuminating the lineage-specific diversification of resin glycoside acylsugars in the morning glory (Convolvulaceae) family using computational metabolomics.

Acylsugars are a class of plant defense compounds produced across many distantly related families. Members of the horticulturally important morning glory (Convolvulaceae) family produce a diverse subclass of acylsugars called resin glycosides (RGs), which comprise oligosaccharide cores, hydroxyacyl chain(s), and decorating aliphatic and aromatic acyl chains. While many RG structures are characterized, the extent of structural diversity of this class in different genera and species is not known. In this study, we asked whether there has been lineage-specific diversification of RG structures in different Convolvulaceae species that may suggest diversification of the underlying biosynthetic pathways. Liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) was performed from root and leaf extracts of 26 species sampled in a phylogeny-guided manner. LC–MS/MS revealed thousands of peaks with signature RG fragmentation patterns with one species producing over 300 signals, mirroring the diversity in Solanaceae-type acylsugars. A novel RG from Dichondra argentea was characterized using nuclear magnetic resonance spectroscopy, supporting previous observations of RGs with open hydroxyacyl chains instead of closed macrolactone ring structures. Substantial lineage-specific differentiation in utilization of sugars, hydroxyacyl chains, and decorating acyl chains was discovered, especially among Ipomoea and Convolvulus—the two largest genera in Convolvulaceae. Adopting a computational, knowledge-based strategy, we further developed a high-recall workflow that successfully explained ~72% of the MS/MS fragments, predicted the structural components of 11/13 previously characterized RGs, and partially annotated ~45% of the RGs. Overall, this study improves our understanding of phytochemical diversity and lays a foundation for characterizing the evolutionary mechanisms underlying RG diversification.

Biological Efficacy of Cochlioquinone-9, a Natural Plant Defense Compound for White-Backed Planthopper Control in Rice.

Simple SummaryThis study investigated the biological efficacy of cochlioquinone-9 (cq-9), a plant secondary metabolite, for controlling white-backed planthopper (WBPH) and compared the gene expression levels following cq-9 treatment. The results show that cq-9 enhances plant growth against WBPH and is associated with aromatic amino acid-related plant defense genes. This demonstrates the potential of cq-9 to replace chemical pesticides and suggests a new method for controlling WBPH.Rice is exposed to various biotic stresses in the natural environment. The white-backed planthopper (Sogatella furcifera, WBPH) is a pest that causes loss of rice yield and threatens the global food supply. In most cases, pesticides are used to control WBPH. However, excessive use of pesticides increases pesticide resistance to pests and causes environmental pollution. Therefore, it is necessary to develop natural product-based pesticides to control WBPH. Plants produce a variety of secondary metabolites for protection. Secondary metabolites act as a defense against pathogens and pests and are valuable as pesticides and breeding materials. Cochlioquinone is a secondary metabolite that exhibits various biological activities, has a negative effect on the growth and development of insects, and contributes to plant defense. Here, we compared plant growth after treatment with cochlioquinone-9 (cq-9), a quinone family member. cq-9 improved the ability of plants to resist WBPH and had an effect on plant growth. Gene expression analysis revealed that cq-9 interacts with various defense-related genes to confer resistance to WBPH, suggesting that it is related to flavonoid compounds. Overall, this study provides insight into the mechanisms of WBPH resistance and suggests that cq-9 represents an environmentally friendly agent for WBPH control.

A beta-glucosidase of an insect herbivore determines both toxicity and deterrence of a dandelion defense metabolite.

Gut enzymes can metabolize plant defense compounds and thereby affect the growth and fitness of insect herbivores. Whether these enzymes also influence feeding preference is largely unknown. We studied the metabolization of taraxinic acid β-D-glucopyranosyl ester (TA-G), a sesquiterpene lactone of the common dandelion (Taraxacum officinale) that deters its major root herbivore, the common cockchafer larva (Melolontha melolontha). We have demonstrated that TA-G is rapidly deglucosylated and conjugated to glutathione in the insect gut. A broad-spectrum M. melolontha β-glucosidase, Mm_bGlc17, is sufficient and necessary for TA-G deglucosylation. Using cross-species RNA interference, we have shown that Mm_bGlc17 reduces TA-G toxicity. Furthermore, Mm_bGlc17 is required for the preference of M. melolontha larvae for TA-G-deficient plants. Thus, herbivore metabolism modulates both the toxicity and deterrence of a plant defense compound. Our work illustrates the multifaceted roles of insect digestive enzymes as mediators of plant-herbivore interactions.

Plant defense compound triggers mycotoxin synthesis by regulating H2B ub1 and H3K4 me2/3 deposition.

Summary Fusarium graminearum produces the mycotoxin deoxynivalenol (DON) which promotes its expansion during infection on its plant host wheat. Conditional expression of DON production during infection is poorly characterized.Wheat produces the defense compound putrescine, which induces hypertranscription of DON biosynthetic genes (FgTRIs) and subsequently leads to DON accumulation during infection. Further, the regulatory mechanisms of FgTRIs hypertranscription upon putrescine treatment were investigated.The transcription factor FgAreA regulates putrescine‐mediated transcription of FgTRIs by facilitating the enrichment of histone H2B monoubiquitination (H2B ub1) and histone 3 lysine 4 di‐ and trimethylations (H3K4 me2/3) on FgTRIs. Importantly, a DNA‐binding domain (bZIP) specifically within the Fusarium H2B ub1 E3 ligase Bre1 othologs is identified, and the binding of this bZIP domain to FgTRIs depends on FgAreA‐mediated chromatin rearrangement. Interestingly, H2B ub1 regulates H3K4 me2/3 via the methyltransferase complex COMPASS component FgBre2, which is different from Saccharomyces cerevisiae.Taken together, our findings reveal the molecular mechanisms by which host‐generated putrescine induces DON production during F. graminearum infection. Our results also provide a novel insight into the role of putrescine during phytopathogen–host interactions and broaden our knowledge of H2B ub1 biogenesis and crosstalk between H2B ub1 and H3K4 me2/3 in eukaryotes.

Intestinal Proteolytic Activity of Pterophylla beltrani Bolívar & Bolívar1 and Its Sensitivity to Cations

Plants can protect themselves by damaging the digestion of insects. However, some insects can activate responses in their digestive system, more specifically in the insect midgut, to deal with plant defense compounds. This is of ecological relevance as a reflection of adaptive capability of insects. This work focused on digestive proteinases of Pterophylla beltrani Bolivar and Bolivar to evaluate if there were differences in expression profiles depending on sex and sensitivity to cations. Intestinal proteolytic activity in P. beltrani adults was determined by a colorimetric assay. Results were related to sex and 2 years of collection (2018 and 2019). Sensitivity was determined using different cations such as Ca, Mg, Mn, and Zn at 100 mM in the reaction mixture of proteolytic activity. Proteolytic activity was stable between years. Most activity was in males in 2019 (256,325 PAU/g) and to a lesser extent in females in 2018 (207,333.33 PAU/g) and 2019 (205,708.3 PAU/g). Proteolytic activity in the presence of Ca, Mg, and Mn was affected to a lesser percentage of 12% of remnant activity but diminished in the presence of Zn (53.7 to 73.5%). Results showed diversity regarding the presence and sensitivity of digestive proteinases in P. beltrani, which is of ecological importance because it could reflect ability to adapt to defenses of plants associated with diet.

Biological performance and biochemical interactions of mustard aphid (Lipaphis erysimi) in Brassica juncea

Present studies were carried out on development and survival of Lipaphis erysimi (Kaltenbach) on diverse Brassica juncea (L.) Czern. & Coss. genotypes, and decipher the role of certain biochemical compounds in plant defense against mustard aphid. There were significant differences among test B. juncea genotypes for total nymphal duration, reproductive period, total developmental period, fecundity and survival of L. erysimi. The development period was significantly longer on PDZM 31, NRCHB 101, RP 7-3-2-2-1, TS 18-5124, RP 11-2-1-3-1, YSG, RLC 3, NPJ 50, IC 355399, MSTWR 17-1, EC 61-9-2-2-2, GP 454 and Kranti, while fecundity and survival were significantly lower on RLC 3, Kranti, IC 355399, Rohini, GP 454, NPJ 50 and TS 18-5124 as compared to other B. juncea genotypes. The biochemical constituents like, total antioxidants, tannins, phenols and FRAP were also significantly higher in RLC 3, Kranti, IC 355399, Rohini, GP 454, NPJ 50 and TS 18-5124 as compared to other B. juncea genotypes, except in a few cases. The total antioxidants and total tannins had significant and negative association, and explained 78.5% and 91.3% variability for fecundity and survival of L. erysimi, indicating their detrimental effects on progeny production and survival of mustard aphid on B. juncea. Present studies suggest that the B. juncea genotypes RLC 3, IC 355399, Rohini, GP 454, NPJ 50, TS 18-5124 and Kranti have higher amounts of test defense biochemicals and impart adverse effects on the reproductive period, fecundity and survival of L. erysimi.

Reduced Infestation by Xylosandrus germanus (Coleoptera: Curculionidae: Scolytinae) in Apple Trees Treated with Host Plant Defense Compounds.

The ambrosia beetle Xylosandrus germanus (Blandford) is an invasive pest that has caused tree decline and death in numerous NY dwarf apple orchards during the past ten years, despite efforts to control them using trunk sprays of chlorpyrifos or pyrethroids, either alone or combined with the repellent verbenone. From 2017 to 2019, we tested trunk applications of different repellents and plant defense compounds for protection against X. germanus in potted apple trees adjacent to infested orchards. Treatments included topical formulations of verbenone and methyl salicylate (MeSa), alone and in combination, at different rates and timings. Additional treatments evaluated included the systemic acquired resistance activators acibenzolar-S-methyl, Reynoutria sachalinensis extract, and salicylic acid. The combination verbenone+MeSa treatments had the lowest incidences of attack sites and galleries containing adults or brood, although results varied among years. In a separate trial, we found no significant difference in numbers of adults caught in ethanol-baited traps placed 5-20 m from an apple bolt treated with the verbenone+MeSa repellent, suggesting that the repellent's effect did not extend to those distances from the treated target. Cross-sectional discs of trunk tissue sampled in August were analyzed for levels of phytohormones. Quantities of ergosterol, abscissic acid, salicylic acid, jasmonic acid, methyl salicylate, methyl jasmonate, trans-cinnamic acid, and indole-3-cinnamic acid did not significantly vary across treatments; however, trees with greater beetle damage contained higher levels of jasmonic and salicylic acid, which are key molecules in plant defense pathways.

Two Apriona Species Sharing a Host Niche Have Different Gut Microbiome Diversity

The adaptability of herbivorous insects to toxic plant defense compounds is partly related to the structure of the gut microbiome. To overcome plant resistance, the insect gut microbiome should respond to a wide range of allelochemicals derived from dietary niches. Nevertheless, for sibling herbivorous insect species, whether the gut microbiome contributes to success in food niche competition is unclear. Based on 16S rDNA high-throughput sequencing, the gut microbiomes of two Apriona species that share the same food niche were investigated in this study to determine whether the gut microbiome contributes to insect success in food-niche competition. Our observations indicated that the gut microbiome tended to play a part in host niche competition between the two Apriona species. The gut microbiome of Apriona swainsoni had many enriched pathways that can help degrade plant toxic secondary compounds, including xenobiotic biodegradation and metabolism, terpenoid and polyketide metabolism, and secondary metabolite biosynthesis. Meanwhile, A. swainsoni hosted a much greater variety of microorganisms and had more viable bacteria than A. germari. We conclude that gut microbes may influence the coevolution of herbivores and host plants. Gut bacteria may not only serve to boost nutritional relationships, but may also play an important role in insect food niche competition.

Sclerotinia sclerotiorum Response to Long Exposure to Glucosinolate Hydrolysis Products by Transcriptomic Approach.

ABSTRACTWhite mold disease, caused by the necrotrophic fungus Sclerotinia sclerotiorum, affects Brassica crops. Brassica crops produce a broad array of compounds, such as glucosinolates, which contribute to the defense against pathogens. From their hydrolysis, several products arise that have antimicrobial activity (GHPs) whose toxicity is structure dependent. S. sclerotiorum may overcome the toxic effect of moderate GHP concentrations after prolonged exposure to their action. Our objective was to identify the molecular mechanism underlying S. sclerotiorum response to long exposure to two chemically diverse GHPs: aliphatic GHP allyl-isothiocyanate (AITC) and indole GHP indol-3-carbinol (I3C). We found that the transcriptomic response is dependent on the type of GHP and on their initial target, involving cell membranes in the case of AITC or DNA in the case of I3C. Response mechanisms include the reorganization of chromatin, mediated by histone chaperones hip4 and cia1, ribosome synthesis controlled by the kinase-phosphatase pair aps1-ppn1, catabolism of proteins, ergosterol synthesis, and induction of detoxification systems. These mechanisms probably help S. sclerotiorum to grow and survive in an environment where GHPs are constantly produced by Brassica plants upon glucosinolate breakdown.IMPORTANCE Brassica species, including important vegetable crops, such as cabbage, cauliflower, or broccoli, or oil crops, such as rapeseed, produce specific chemical compounds useful to protect them against pests and pathogens. One of the most destructive Brassica diseases in temperate areas around the world is Sclerotinia stem rot, caused by the fungus Sclerotinia sclerotiorum. This is a generalist pathogen that causes disease over more than 400 plant species, being a serious threat to economically important crops worldwide, including potato, bean, soybean, and sunflower, among many others. Understanding the mechanisms utilized by pathogens to overcome specific plant defensive compounds can be useful to increase plant resistance. Our study demonstrated that Sclerotinia shows different adaptation mechanisms, including detoxification systems, to grow and survive when plant protective compounds are present.

Elicitor Application in Strawberry Results in Long-Term Increase of Plant Resilience Without Yield Loss.

For a first step integrating elicitor applications into the current IPM strategy increasing plant resilience against pests, we investigated repeated elicitor treatments in a strawberry everbearer nursery and cropping cycle under glass. During nursery methyl-jasmonate (MeJA), testing induction of defenses with plant bioassays was applied every 3 weeks. Thrips damage and reproduction by spider mites, whitefly and aphids were strongly reduced upon elicitor treatment. Subsequently, we applied MeJA every 3 weeks or based on scouting pests during a whole cropping cycle. Thrips leaf bioassays and LC-MS leaf metabolomics were applied to investigate the induction of defenses. Leaf damage by thrips was lower for both MeJA application schemes compared to the control except for the last weeks. While elicitor treatments after scouting also reduced damage, its effect did not last. Thrips damage decreased from vegetative to mature plants during the cropping cycle. At the end of the nursery phase, plants in the elicitor treatment were smaller. Surprisingly, growth during production was not affected by MeJA application, as were fruit yield and quality. LC-MS leaf metabolomics showed strong induction of vegetative plants decreasing during the maturation of plants toward the end of cultivation. Concurrently, no increase in the JA-inducible marker PPO was observed when measured toward the end of cultivation. Mostly flavonoid and phenolic glycosides known as plant defense compounds were induced upon MeJA application. While induced defense decreased with the maturation of plants, constitutive defense increased as measured in the leaf metabolome of control plants. Our data propose that young, relatively small plant stages lack constitutive defense necessitating an active JA defense response. As plants, mature constitutive defense metabolites seem to accumulate, providing a higher level of basal resistance. Our results have important implications for but are not limited to strawberry cultivation. We demonstrated that repeated elicitor application could be deployed as part of an integrated approach for sustainable crop protection by vertical integration with other management tactics and horizontal integration to control multiple pests concurrently. This approach forms a promising potential for long-term crop protection in greenhouses.

Transcriptional up-regulation of host-specific terpene metabolism in aphid-induced galls of Pistacia palaestina.

Galling insects gain food and shelter by inducing specialized anatomical structures in their plant hosts. Such galls often accumulate plant defensive metabolites protecting the inhabiting insects from predation. We previously found that, despite a marked natural chemopolymorphism in natural populations of Pistacia palaestina, the monoterpene content in Baizongia pistaciae-induced galls is substantially higher than in leaves of their hosts. Here we show a general up-regulation of key structural genes in both the plastidial and cytosolic terpene biosynthetic pathways in galls as compared with non-colonized leaves. Novel prenyltransferases and terpene synthases were functionally expressed in Escherichia coli to reveal their biochemical function. Individual Pistacia trees exhibiting chemopolymorphism in terpene compositions displayed differential up-regulation of selected terpene synthase genes, and the metabolites generated by their gene products in vitro corresponded to the monoterpenes accumulated by each tree. Our results delineate molecular mechanisms responsible for the formation of enhanced monoterpene in galls and the observed intraspecific monoterpene chemodiversity displayed in P. palaestina. We demonstrate that gall-inhabiting aphids transcriptionally reprogram their host terpene pathways by up-regulating tree-specific genes, boosting the accumulation of plant defensive compounds for the protection of colonizing insects.

LaPT2 Gene Encodes a Flavonoid Prenyltransferase in White Lupin.

Legume plants are rich in prenylated flavonoid compounds, which play an important role in plant defense and human health. In the present study, we identified a prenyltransferase (PT) gene, named LaPT2, in white lupin (Lupinus albus), which shows a high identity and close relationship with the other known PT genes involved in flavonoid prenylation in planta. The recombinant LaPT2 protein expressed in yeast cells exhibited a relatively strong activity toward several flavonols (e.g., kaempferol, quercetin, and myricetin) and a relatively weak activity toward flavanone (naringenin). In addition, the recombinant LaPT2 protein was also active toward several other types of flavonoids, including galangin, morin, 5-deoxyquercetin, 4'-O-methylkaempferol, taxifolin, and aromadendrin, with distinct enzymatic affinities. The LaPT2 gene was preferentially expressed in the roots, which is consistent with the presence of prenylated flavonoid kaempferol in the roots. Moreover, we found that the expression level of LaPT2 paralleled with those of LaF3H1 and LaFLS2 genes that were relatively higher in roots and lower in leaves, suggesting that they were essential for the accumulation of prenylated flavonoid kaempferol in roots. The deduced full-length LaPT2 protein and its signal peptide fused with a green fluorescent protein (GFP) are targeted to plastids in the Arabidopsis thaliana protoplast. Our study demonstrated that LaPT2 from white lupin is responsible for the biosynthesis of prenylated flavonoids, in particular flavonols, which could be utilized as phytoalexin for plant defense and bioactive flavonoid compounds for human health.

Consistent pattern of higher lability of leaves from high latitudes for both native Phragmites australis and exotic Spartina alterniflora

Abstract Global variation in litter decomposition rates is driven by climate, decomposer taxa and litter quality. Most large‐scale studies of litter quality have made comparisons across species, rather than within a species sourced from different latitudes. Here, we aim to explore latitudinal variation in leaf litter decomposition rate and litter quality within a species. We investigated whether the typical interspecific pattern of increased litter lability at higher latitudes also holds within plant species, by comparing leaf litter decomposition rates and litter traits from stands of native Phragmites australis and exotic Spartina alterniflora in Chinese coastal wetlands spanning 20° of latitude using parallel greenhouse and field transplant experiments. We found that leaf litter from high‐latitude plants decomposed 46.6 ± 5.1% faster than that from low‐latitude conspecifics, with similar patterns in both plant species in both decomposition experiments. Higher lability of leaves from high latitudes was associated with lower levels of plant defensive compounds (phenolics and tannins) and higher levels of nutrients (Ca, Mg and Na). Litter from the exotic S. alterniflora decomposed faster than litter from the native P. australis, being consistent with lower defences and higher nutrient concentrations in S. alterniflora litter. Our results show that individual species follow the same pattern of increasing litter lability at higher latitudes previously reported in cross‐species geographical comparisons. Moreover, this pattern can develop rapidly (<4 decades) in an introduced species, raising the question of whether it is caused by phenotypic plasticity or adaptation. A free Plain Language Summary can be found within the Supporting Information of this article.

Sugar transporters enable a leaf beetle to accumulate plant defense compounds

Many herbivorous insects selectively accumulate plant toxins for defense against predators; however, little is known about the transport processes that enable insects to absorb and store defense compounds in the body. Here, we investigate how a specialist herbivore, the horseradish flea beetle, accumulates glucosinolate defense compounds from Brassicaceae in the hemolymph. Using phylogenetic analyses of coleopteran major facilitator superfamily transporters, we identify a clade of glucosinolate-specific transporters (PaGTRs) belonging to the sugar porter family. PaGTRs are predominantly expressed in the excretory system, the Malpighian tubules. Silencing of PaGTRs leads to elevated glucosinolate excretion, significantly reducing the levels of sequestered glucosinolates in beetles. This suggests that PaGTRs reabsorb glucosinolates from the Malpighian tubule lumen to prevent their loss by excretion. Ramsay assays corroborated the selective retention of glucosinolates by Malpighian tubules of P. armoraciae in situ. Thus, the selective accumulation of plant defense compounds in herbivorous insects can depend on the ability to prevent excretion.

Disarming the Host: Detoxification of Plant Defense Compounds During Fungal Necrotrophy.

While fungal biotrophs are dependent on successfully suppressing/subverting host defenses during their interaction with live cells, necrotrophs, due to their lifestyle are often confronted with a suite of toxic metabolites. These include an assortment of plant defense compounds (PDCs) which can demonstrate broad antifungal activity. These PDCs can be either constitutively present in plant tissue or induced in response to infection, but are nevertheless an important obstacle which needs to be overcome for successful pathogenesis. Fungal necrotrophs have developed a number of strategies to achieve this goal, from the direct detoxification of these compounds through enzymatic catalysis and modification, to the active transport of various PDCs to achieve toxin sequestration and efflux. Studies have shown across multiple pathogens that the efficient detoxification of host PDCs is both critical for successful infection and often a determinant factor in pathogen host range. Here, we provide a broad and comparative overview of the various mechanisms for PDC detoxification which have been identified in both fungal necrotrophs and fungal pathogens which depend on detoxification during a necrotrophic phase of infection. Furthermore, the effect that these mechanisms have on fungal host range, metabolism, and disease control will be discussed.