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-lle levels.

The circadian clock contributes to diurnal patterns of plant indirect defense in nature

The plant circadian clock regulates the rhythms of plant metabolism.Many herbivore-induced plant volatiles(HIPVs)fluctuate,diurnally,but the role of the circadian clock in the emission of HIPVs and their ecological consequences remains largely unknown.Here,we show that the timing of herbivore attack can alter the outcome of tri-trophic interactions,and this is mediated by the circadian clock,under both field and glasshouse conditions.Although most HIPV emissions did not have a circadian rhythm,the circadian clock modulated HIPV emissions in a time-dependent manner.HIPVs mediate tri-trophic interactions,and the circadian clock may affect these interactions by modulating HIPV emission in nature.

Shifting Nicotiana attenuata's diurnal rhythm does not alter its resistance to the specialist herbivore Manduca sexta

Arabidopsis thaliana plants are less resistant to attack by the generalist lepidopteran herbivore Trichoplusia ni when plants and herbivores are entrained to opposite, versus identical diurnal cycles and tested under constant conditions. This effect is associated with circadian fluctuations in levels of jasmonic acid, the transcription factor MYC2, and glucosinolate contents in leaves. We tested whether a similar effect could be observed in a different plant-herbivore system： the wild tobacco Nicotiana attenuata and its co-evolved specialist herbivore, Manduca sexta. We measured larval growth on plants under both constant and diurnal conditions following identical or opposite entrainment, profiled the metabolome of attacked leaf tissue, quantified specific metabolites known to reduce M. sexta growth, and monitored A/I. sexta feeding activity under all experimental conditions. Entrainment did not consistently affect NI. sexta growth or plant defense induction. However, both were reduced under constant dark conditions,as was M. sexta feeding activity. Our data indicate that the response induced by NI. sexta in N. attenuata is robust to diurnal cues and independent of plant or herbivore entrain- ment. We propose that while the patterns of constitutive or general damage-induced defense may undergo circadian fluctuation, the orchestration of specific induced responses is more complex.

NaMYB8 regulates distinct,optimally distributed herbivore defense traits

When herbivores attack, plants specifically reconfigure their metabolism. Herbivory on the wild tobacco Nicotiana attenuata strongly induces the R2R3 MYB transcriptional activator MYB8, which was reported to specifically regulate the accumulation of phenolamides （PAs）. We discovered that transcriptional regulation of trypsin protease inhibitors （TPIs） and a threonine deaminase （TD） also depend on MYB8 expression. Induced distributions of PAs, TD and TPIs all meet predictions of optimal defense theory： their leaf concentrations increase with the fitness value and the probability of attack of the tissue. Therefore, we suggest that these defensive compounds have evolved to be co-regulated by MYB8.

Natural variation in linalool metabolites:One genetic locus,many functions?

The ubiquitous volatile linalool is metabolized in plants to nonvolatile derivatives.We studied Nicotiana attenuata plants which naturally vary in(S)-(+)-linalool contents,and lines engineered to produce either(R)-(-)-or(S)-(+)-linalool.Only(S)-(+)-linalool production was associated with slower growth of a generalist herbivore,and a large fraction was present as nonvolatile derivatives.We found that variation in volatile linalool and its nonvolatile glycosides mapped to the same genetic locus which harbored the biosynthetic gene,NaLIS,but that free linalool varied more in environmental responses.This study reveals how(S)-(+)-linalool and conjugates differ in their regulation and possible functions in resistance.

Sex ratio of mirid populations shifts in response to hostplant co-infestation or altered cytokinin signaling

Herbivore species sharing a host plant often compete. In this study, we show that host plant-mediated interaction between two insect herbivores-a generalist and a specialist-results in a sex ratio shift of the specialist＇s offspring. We studied demographic parameters of the specialist Tupiocoris notatus（Hemiptera： Miridae）when co-infesting the host plant Nicotiana attenuata（Solanaceae） with the generalist leafhopper Empoasca sp.（Hemiptera： Cicadellidae）. We show that the usually female-biased sex ratio of T. notatus shifts toward a higher male proportion in the offspring on plants coinfested by Empoasca sp. This sex ratio change did not occur after oviposition, nor is it due differential mortality of female and male nymphs. Based on pyrosequencing and PCR of bacterial 16 S rRNA amplicons, we concluded that sex ratio shifts were unlikely to be due to infection with Wolbachia or other known sex ratio-distorting endosymbionts. Finally, we used transgenic lines of N.attenuata to evaluate if the sex ratio shift could be mediated by changes in general or specialized host plant metabolites. We found that the sex ratio shift occurred on plants deficient in two cytokinin receptors（irCHK2/3）.Thus, cytokinin-regulated traits can alter the offspring sex ratio of the specialist T.notatus.