Nicotine's Defensive Function in Nature

Plants produce metabolites that directly decrease herbivore performance, and as a consequence, herbivores are selected for resistance to these metabolites. To determine whether these metabolites actually function as defenses requires measuring the performance of plants that are altered only in the production of a certain metabolite. To date, the defensive value of most plant resistance traits has not been demonstrated in nature. We transformed native tobacco(Nicotiana attenuata) with a consensus fragment of its two putrescine N-methyl transferase (pmt) genes in either antisense or inverted-repeat (IRpmt) orientations. Only the latter reduced (by greater than 95%) constitutive and inducible nicotine. With D₄-nicotinic acid (NA), we demonstrate that silencing pmt inhibits nicotine production, while the excess NA dimerizes to form anatabine. Larvae of the nicotine-adapted herbivore Manduca sexta (tobacco hornworm) grew faster and, like the beetle Diabrotica undecimpunctata, preferred IRpmt plants in choice tests. When planted in their native habitat, IRpmt plants were attacked more frequently and, compared to wild-type plants, lost 3-fold more leaf area from a variety of native herbivores, of which the beet armyworm, Spodoptera exigua, and Trimerotropis spp. grasshoppers caused the most damage. These results provide strong evidence that nicotine functions as an efficient defense in nature and highlights the value of transgenic techniques for ecological research.     

Environmentally sustainable pest control options for Drosophila suzukii

The spotted‐wing drosophila or cherry vinegar fly (Drosophila suzukii) is native to Asia but has invaded other continents since 2008 and has spread throughout Europe. The females have a serrated ovipositor allowing them to penetrate the skins of intact ripening fruits to deposit their eggs, and the developing larvae rapidly destroy the fruits close to harvest. Drosophila suzukii has a rapid life cycle and the larvae develop well beneath the fruit surface. This means that the use of pesticides is problematic and often not effective, first due to their restricted use close to harvest to protect consumers, and second because the larvae are deep enough inside the fruit to avoid contact. There are currently no effective and environmentally sustainable pest control methods for this species, resulting in extensive damage to fruit crops. Here, we review the current status of D. suzukii as a fruit crop pest and discuss the feasibility of current pesticide‐free control methods. We also consider the potential of new technologies as a basis for the urgently needed specific and long‐term control of this species.     

Physiological integration of roots and shoots in plant defense strategies links above- and belowground herbivory

Roots play a critical, but largely unappreciated, role in aboveground anti-herbivore plant defense (e.g. resistance and tolerance) and root–leaf connections may therefore result in unexpected coupling between above- and belowground consumers. Using the tobacco ( Nicotiana tabacum ) system we highlight two examples of this phenomenon. First, the secondary metabolite nicotine is produced in roots, yet translocated aboveground for use as a foliar resistance trait. We demonstrate that nematode root herbivory interferes with foliar nicotine dynamics, resulting in positive effects on aboveground phytophagous insects. Notably, nematode-induced facilitation only occurred on nicotine-producing plants, and not on nicotine-deficient mutants. In the second case, we use stable isotope and invertase enzyme analyses to demonstrate that foliar herbivory elicits a putative tolerance response whereby aboveground nutritional reserves are allocated to roots, resulting in facilitation of phytoparasitic nematodes. Thus, plants integrate roots in resistance and tolerance mechanisms for leaf defense, and such root–leaf connections inherently link the dynamics of above- and belowground consumers.     

Shared signals -'alarm calls' from plants increase apparency to herbivores and their enemies in nature

The attraction of natural enemies of herbivores by volatile organic compounds as an induced indirect defence has been studied in several plant systems. The evidence for their defensive function originates mainly from laboratory studies with trained parasitoids and predators; the defensive function of these emissions for plants in natural settings has been rarely demonstrated. In native populations and laboratory Y-tube choice experiments with transgenic Nicotiana attenuata plants unable to release particular volatiles, we demonstrate that predatory bugs use terpenoids and green leaf volatiles (GLVs) to locate their prey on herbivore-attacked plants. By attracting predators with volatile signals, this native plant reduces its herbivore load – demonstrating the defensive function of herbivore-induced volatile emissions. However, plants producing GLVs are also damaged more by flea beetles. The implications of these conflicting ecological effects for the evolution of induced volatile emissions and for the development of sustainable agricultural practices are discussed.     

Jasmonate signaling makes flowers attractive to pollinators and repellant to florivores in nature

Flowers are required for the Darwinian fitness of flowering plants,but flowers’advertisements for pollination services can attract florivores.Previous glasshouse work with Nicotiana attenuata revealed the role of jasmonate(JA)signaling in flower development,advertisement and defense.However,whether JA signaling mediates flowers’filtering of floral visitors in nature remained unknown.This field study revealed that silencing JA signaling resulted in flowers that produce less nectar and benzyl acetone,two pollinatorattractive traits.Meanwhile,flowers of defenseless plants were highly attacked by a suite of native herbivores,and damage to buds in native plants correlated negatively with their JA-Ile levels.Letter to the Editor     

Overcompensating plants: their expression of resistance traits and effects on herbivore preference and performance

Overcompensation is a plant tolerance response in which plants have higher fitness after herbivory than without damage. Although it has been demonstrated that plants are able to simultaneously express resistance and tolerance traits, it remains unclear whether overcompensating plants are also inducing resistance‐mediating secondary metabolite production and how herbivores perform on plants that overcompensate. Our previous work has shown that a potato variety [Solanum tuberosum L. cv. Pastusa Suprema (Solanaceae)] from Colombia can express overcompensatory responses to damage by larvae of the Guatemalan potato moth, Tecia solanivora Povolny (Lepidoptera: Gelechiidae). Here we investigated (1) whether potatoes that express overcompensatory responses also induce resistance traits and (2) how the previous damage affects Guatemalan potato moth preference and performance. Our results show that larval feeding not only systemically induces higher tuber biomass but also an increased production of resistance‐related compounds, such as phenolics and proteinase inhibitors. Pupal mass increased with increasing tuber size, whereas changes in tuber secondary metabolism did not correlate with any metric of larval performance. Oviposition preference did not change between induced and undamaged plants. Our data show that potato plants expressing overcompensatory responses also induce secondary compounds known to increase resistance against herbivores. However, the induced response was relatively small, reducing the opportunities for a negative effect on the herbivore. Hypotheses for why larvae perform better in larger tubers and are not affected by the secondary metabolism are discussed. From an ecological and agricultural point of view, our results suggest that the expression of overcompensatory traits could have positive effects on herbivore performance.     

The major shifts of human duplicated genes

Since many gene duplications in the human genome are ancient duplications going back to the origin of vertebrates, the question may be asked about the fate of such duplicated genes at the compositional genome transitions that occurred between cold- and warm-blooded vertebrates. Indeed, at that transition, about half of the (GC-poor) genes of cold-blooded vertebrates (the genes of the gene-dense "ancestral genome core") underwent a GC enrichment to become the genes of the "genome core" of warm-blooded vertebrates. Since the compositional distribution of the human duplicated genes investigated (1111 pairs) mimics the general distribution of human genes (about 50% GC(3)-poor and 50% GC(3)-rich genes, the border being at 60% GC(3)), we considered two possibilities, namely that the compositional transition affected either (i) about half of the copies on a random basis, or (ii) preferentially only one copy of the duplicated genes. The two possibilities could be distinguished if each copy is put into one of two subsets according to its GC(3) level. Indeed, in the first case, the two distributions would be similar, whereas in the second case, the two distributions would be different, one copy having maintained the ancestral GC-poor composition, and one copy having undergone the compositional change. Using this approach, we could show that, by far and large, one copy of the duplicated genes preferentially underwent the GC enrichment. This result implies that this copy, which had possibly acquired a different function and/or regulation, was preferentially translocated into the gene-dense compartment of the genome, the "ancestral genome core", namely the "gene space" which underwent the compositional transition at the emergence of warm-blooded vertebrates.