Defense Expression Research Articles

Coevolutionary arms race versus host defense chase in a tropical herbivore–plant system

Coevolutionary models suggest that herbivores drive diversification and community composition in plants. For herbivores, many questions remain regarding how plant defenses shape host choice and community structure. We addressed these questions using the tree genus Inga and its lepidopteran herbivores in the Amazon. We constructed phylogenies for both plants and insects and quantified host associations and plant defenses. We found that similarity in herbivore assemblages between Inga species was correlated with similarity in defenses. There was no correlation with phylogeny, a result consistent with our observations that the expression of defenses in Inga is independent of phylogeny. Furthermore, host defensive traits explained 40% of herbivore community similarity. Analyses at finer taxonomic scales showed that different lepidopteran clades select hosts based on different defenses, suggesting taxon-specific histories of herbivore-host plant interactions. Finally, we compared the phylogeny and defenses of Inga to phylogenies for the major lepidopteran clades. We found that closely related herbivores fed on Inga with similar defenses rather than on closely related plants. Together, these results suggest that plant defenses might be more evolutionarily labile than the herbivore traits related to host association. Hence, there is an apparent asymmetry in the evolutionary interactions between Inga and its herbivores. Although plants may evolve under selection by herbivores, we hypothesize that herbivores may not show coevolutionary adaptations, but instead "chase" hosts based on the herbivore's own traits at the time that they encounter a new host, a pattern more consistent with resource tracking than with the arms race model of coevolution.

Book Review: A Right to Offend: Free Expression in the Twenty-First Century, by Brian Winston

A Right to Offend: Free Expression in Twenty-First Century . Brian Winston. London, UK: Bloomsbury Academic, 2012. 432 pp. $140 hbk. $40.95 pbk.The year 2013 is an especially fitting time to review a book about offensive expres- sion. It is, after all, 25th anniversary of U.S. Supreme Court's landmark ruling in Hustler Magazine v. Falwell. That decision protected pornographer Larry Flynt's right under First Amendment to U.S. Constitution to parodically suggest that Reverend Jerry Falwell, head of Moral Majority and Thomas Road Baptist Church, had sex with his mother in a fly-infested outhouse and preached while drunk. The parody closed with Falwell rhetorically querying, You don't think I could lay down that bullshit sober, do you?The right to offend, however, is no laughing matter today across much of world, given a number of sobering events. For instance, deadly violent protests in September 2012 in response to a low-budget, anti-Islamic video called Innocence of Muslims demonstrate that whether such a right even exists in some countries and cultures is very much in doubt. It is into such turbulent waters that Brian Winston's timely tome, A Right to Offend, wades deeply, internationally, and comprehensively.Spanning more than 400 pages, book covers a vast amount of territory, from censorship of writings of Martin Luther in 1500s through so-called Hackgate scandal of 2011 involving Rupert Murdoch's News of World and journalists infil- trating cell phone messages and texts of dozen of individuals. In between are more than three dozen incidents and controversies involving censorship in United Kingdom and United States that serve as pegs for author's points.The book includes an eclectic mix of characters, from double A (Julian Assange and Amos nAndy) to double Z (John Peter Zenger and Emile Zola). And, yes, Falwell case is discussed, but only briefly and standing for obvious yet important proposition that had Supreme Court ruled for reverend, all American televi- sion satire from Saturday Night Live through to The Daily Show with Jon Stewart might well have been jeopardized.Despite wide range of material covered, book charts a clear trajectory. Part I reveals what Winston calls prosecution of free expression, while Part II comes to free expression's defense. Winston ultimately concludes with ten bullet-pointed suggestions supporting his fundamental belief that the right to free speech and right within it to offend, because without it we have no free speech, must be main- tained. At whatever cost.Winston's thesis is well articulated. While he once believed right to engage in offensive expression had been firmly won in Western Europe and United States, that changed in February 1989 when Iman Ruhollah al-Musavi al-Khomeni issued a fatwa targeting Salman Rushdie for his novel, The Satanic Verses. For Winston, who points out that a copy of Rushdie's book lies on desk as this is being typed, fatwa was a game-changer that created a new template for anybody affronted by a specific act of free expression to respond with an aggression previously unseen, via its extra-territorial, quasi-judicial sanctioning of mob rule and murder to suppress expression. …

Remote sensing of future competitors: Impacts on plant defenses

Far-red radiation (FR) reflected by green tissues is a key signal that plants use to detect the proximity of future competitors. Perception of increased levels of FR elicits a suite of responses collectively known as the shade-avoidance syndrome, which includes increased stem elongation, production of erect leaves, and reduced lateral branching. These responses improve the access to light for plants that occur in crowded populations. Responses to the proximity of competitors are known to affect the susceptibility to disease and predation in several organisms, including social animals. However, the impacts of warning signals of competition on the expression of defenses have not been explicitly investigated in plants. In the experiments reported here, we show that reflected FR induced a dramatic down-regulation of chemical defenses in wild tobacco (Nicotiana longiflora). FR altered the expression of several defense-related genes, inhibited the accumulation of herbivore-induced phenolic compounds, and augmented the performance of the specialist herbivore Manduca sexta. Complementary studies with tomato suggested that the effects of FR on defenses are mediated by the photoreceptor phytochrome B. The central implication of these results is that shade-intolerant species such as wild tobacco and tomato activate functional changes that affect their ability to cope with herbivore attack in response to phytochrome signals of future competition, even in the absence of real competition for resources. These findings suggest that competition overshadowed herbivory during the evolution of this group of species and add a new axis to the definition of the shade-avoidance syndrome.

Plasma membrane-cell wall adhesion is required for expression of plant defense responses during fungal penetration.

Fungal pathogens almost invariably trigger cell wall-associated defense responses, such as extracellular hydrogen peroxide generation and callose deposition, when they attempt to penetrate either resistant or susceptible plant cells. In the current study, we provide evidence that the expression of these defenses is dependent on adhesion between the plant cell wall and the plasma membrane. Peptides containing an Arg-Gly-Asp (RGD) motif, which interfered with plasma membrane-cell wall adhesion as shown by the loss of the thin plasma membrane-cell wall connections known as Hechtian strands, reduced the expression of cell wall-associated defense responses during the penetration of nonhost plants by biotrophic fungal pathogens. This reduction was associated with increased fungal penetration efficiency. Neither of these effects was seen after treatment with similar peptides lacking the RGD motif. Disruption of plant microfilaments had no effect on Hechtian strands but mimicked the effect of RGD peptides on wall defenses, suggesting that the expression of cell wall-associated defenses involves communication between the plant cell wall and the cytosol across the plasma membrane. To visualize the state of the plasma membrane-cell wall interaction during fungal penetration, we observed living cells during sucrose-induced plasmolysis. In interactions that were characterized by the early expression of cell wall-associated defenses, there was no change, or an increase, in plasma membrane-cell wall adhesion under the penetration point as the fungus grew through the plant cell wall. In contrast, for rust fungus interactions with host plants, there was a strong correlation between a lack of cell wall-associated defenses and a localized decrease in plasma membrane-cell wall adhesion under the penetration point. Abolition of this localized decreased adhesion by previous inoculation with a fungus that increased plasma membrane-cell wall adhesion resulted in reduced penetration by the rust fungus and induction of cell wall-associated defenses. These results suggest that rust fungi may induce a decrease in plasma membrane-cell wall adhesion as a means of disrupting the expression of nonspecific defense responses during penetration of host cells.