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Pathogenesis-related (PR) proteins play important roles in plant defense response. However, functional investigation of PR10 genes is still limited and their physiological roles have not been conclusively characterized in biological processes of conifer trees. Here, we identified multiple novel members in the western white pine (Pinus monticola) PmPR10 family by bioinformatic mining available transcriptomic data. Phylogenetic analysis of protein sequences revealed four PR10 and two PR10-like clusters with a high synteny across different species of five-needle pines. Of 10 PmPR10 genes, PmPR10-3.1 was selected and expressed in Escherichia coli. The purified recombinant protein exhibited inhibitory effects on spore hyphal growth of fungal pathogens Cronartium ribicola, Phoma exigua, and Phoma argillacea by in-vitro anti-fungal analysis. Genetic variation analysis detected a total of 21 single nucleotide polymorphisms (SNPs) within PmPR10-3.1 in a collection of P. monticola seed families. A nonsynonymous SNP (t178g) showed significant association with relative levels of quantitative disease resistance (QDR), explaining about 8.7% of phenotypic variation as the peak value across all SNPs. Our results provide valuable insight into the genetic architecture underlying P. monticola QDR and imply that PmPR10-3.1 may function as an important component in conifer basal immunity for non-specific resistance to a wide spectrum of pathogens. Key words: association analysis, in-vitro anti-fungal array, pathogenesis-related protein family 10, quantitative disease resistance, white pine blister rust. Les proteines liees a la pathogenese (PR) jouent des roles importants dans les reactions de defense des plantes. Cependant, les etudes fonctionnelles des genes PR10 demeurent limitees et leurs roles physiologiques n'ont pas encore ete caracterises definitivement dans les processus biologiques chez les coniferes. Dans ce travail, les auteurs identifient de nombreux membres inedits de la famille PmPR10 chez le pin argente (Pinus monticola) par exploitation bioinformatique de donnees transcriptomiques disponibles. Une analyse phy-logenetique des sequences proteiques a revele quatre amas de genes PR10 et deux amas de genes ressemblant a PR10, lesquels presentaient un fort degre de syntenie chez differentes especes de pins a cinq aiguilles. Des 10 genes PmPR10, PmPr10-3.1 a ete choisi et exprime chez Escherichia coli. La proteine recombinante purifiee presentait une activite inhibitrice sur la croissance des hyphes hors de la spore chez des pathogenes fongiques (Cronartium rubicola, Phoma exigua et Phoma argilacea)lors de tests d'activite antifongique realises in vitro. Une analyse de la variation genetique a detecte 21 polymorphismes mononucleotidiques (SNP) au sein de PmPR10-3.1 parmi une collection de familles de graines du P. monticola. Un SNP synonyme (t178g) montrait une association significative avec les niveaux relatifs de resistance quantitative (QDR), et expliquait environ 8,7 % de la variation phenotypiques et etait le plus fortement associe de tous les SNP. Ces resultats jettent un eclairage sur l'architecture genetique sous-tendant la QDR chez le P. monticola et impliquent que PmPR10-3.1 pourrait constituer une composante importante de l'immunite basale chez les coniferes en ce qui a trait a une resistance non-specifique contre un large spectre de pathogenes. [Traduit par la Redaction] Mots-cles: analyse d'association, activite antifongique in vitro, famille PR10 de proteines liees a la pathogenese, resistance quantitative, rouille vesiculeuse du pin blanc., Introduction Pathogenesis-related (PR) proteins are important components involved in host defense responses to protect plants from environmental biotic and abiotic stressors. PR proteins are grouped into different families based on [...]

Recent studies indicate that thiamethoxam (TMX), a neonicotinoid insecticide, can affect plant responses to environmental stressors, such as neighboring weeds. The molecular mechanisms behind both stable and environmentally specific responses to TMX likely involve genes related to defense and stress responses. We investigated the effect of a TMX seed treatment on global gene expression in maize coleoptiles both under normal conditions and under low ratio red to far-red (R:FR) light stress induced by the presence of neighboring plants. The neighboring plant treatment upregulated genes involved in biotic and abiotic stress responses and affected specific photosynthesis and cell-growth related genes. Low R:FR light may enhance maize resistance to herbivores and pathogens. TMX appears to compromise resistance. The TMX treatment stably repressed many genes that encode proteins involved in biotic stress responses, as well as cell-growth genes. Notably, TMX effects on many genes' expression were conditional on the environment. In response to low R:FR, plants treated with TMX engage genes in the JA pathway, as well as other stress-related response pathways. Neighboring weeds may condition TMX-treated plants to become more stress tolerant. Key words: maize, thiamethoxam, plant defense, jasmonic acid, shade avoidance. De récentes études indiquent que le thiaméthoxame (TMX), un insecticide néonicotinoïde, peut affecter la réponse des plantes aux stress environnementaux tels que les adventices. Les mécanismes moléculaires sur lesquels reposent ces réponses au TMX, lesquelles s'avèrent àlafois stables et spécifiques d'un environnement, impliquent vraisemblablement des gènes jouant des rôles dans la réponse aux stress et dans la défense. Les auteurs ont étudié l'effet d'un traitement de semence avec le TMX sur l'expression génique globale chez des coléoptiles du maïs poussant tant en conditions normales que sous stress lumineux (faible ratio de rouge à rouge lointain; R/FR) induit par la présence d'adventices à proximité. Le traitement avec adventices a haussé l'expression de gènes impliqués dans la réponse aux stress biotiques et abiotiques, et il a aussi affecté des gènes spécifiques impliqués dans la photosynthèse et la croissance cellulaire. Un ratio R/FR faible pourrait ainsi accroître la résistance du maïs aux herbivores et aux agents pathogènes. Le TMX semble compromettre cette résistance. Le traitement TMX a permis de baisser de manière stable l'expression de plusieurs gènes qui codent pour des protéines impliquées dans les réponses aux stress biotiques ainsi que des gènes liés à la croissance cellulaire. Notamment, le TMX a affecté l'expression de plusieurs gènes en fonction de l'environnement. En réponse à un faible ratio R/FR, les plantes traitées au TMX font appel à des gènes dans les sentiers de l'AJ ainsi que d'autres sentiers de réponse aux stress. La présence d'adventices à proximité pourrait rendre les plantes traitées au TMX plus tolérantes aux stress. [Traduit par la Rédaction] Mots-clés: maïs, thiaméthoxame, défense des plantes, acide jasmonique, évitement de l'ombre., Introduction Crop-weed competition is a major source of yield loss (Liu et al. 2009). Even if unshaded, plants can sense neighboring vegetation by the change in light quality and can [...]

Abstract: Narrow-sense heritability (portion of the total phenotypic variation attributable to additive genetic effect, [h.sup.2]) is a critical parameter in plant breeding and genetics, but its estimation is difficult for [...]

Abstract: Leafminer (Liriomyza langei) is a major insect pest of many important agricultural crops, including spinach (Spinacia oleracea). Use of genetic resistance is an efficient, economic, and environment-friendly method to [...]

Wounded leaves communicate their damage status to one another through a poorly understood process of long-distance signalling. This stimulates the distal production of jasmonates, potent regulators of defence responses. Using non-invasive electrodes we mapped surface potential changes in Arabidopsis thaliana after wounding leaf eight and found that membrane depolarizations correlated with jasmonate signalling domains in undamaged leaves. Furthermore, current injection elicited jasmonoyl-isoleucine accumulation, resulting in a transcriptome enriched in RNAs encoding key jasmonate signalling regulators. From among 34 screened membrane protein mutant lines, mutations in several clade 3 GLUTAMATE RECEPTOR-LIKE genes (GLRs 3.2, 3.3 and 3.6) attenuated wound-induced surface potential changes. Jasmonate-response gene expression in leaves distal to wounds was reduced in a glr3.3 glr3.6 double mutant. This work provides a genetic basis for investigating mechanisms of long-distance wound signalling in plants and indicates that plant genes related to those important for synaptic activity in animals function in organ-to-organ wound signalling., Unlike plants, animals rely on rapid nervous systems to escape predation. A stationary fly that perceives danger takes less than 300 ms to take off, and this process requires complex [...]

Plants undergo changes in response to biotic and abiotic stresses that help them adjust and survive. Some of these changes may even be passed on to progeny and eventually lead to adaptive evolution. Transgenerational changes in response to stress include alterations in DNA methylation and changes in homologous recombination frequency (HRF). The progeny of plants that were stressed often show elevated HRF as well as genomic hypermethylation, although specific loci that are beneficial in times of stress may be hypomethylated. One of the possible mechanisms responsible for passing the memory to the progeny involves small interfering RNAs; Dicer-like proteins, DCL2 and DCL3, are in part required for this process. However, while epigenetic modifications are often present in the untreated progeny of stressed plants, they are not usually sustained for multiple unexposed generations. Still, transgenerational inheritance of such changes has already begun to provide evidence for an important role of epigenetics in enhancing stress resistance. Key words: homologous recombination, DNA methylation, plant stress response, epigenetic regulation, transgenerational effect, adaptive evolution. Les vegetaux subissent des changements en reponse a des stress biotiques et abiotiques qui les aident a s'ajuster et a survivre. Certains de ces changements peuvent meme etre transmis a leur progeniture et conduire eventuellement a une evolution adaptative. Les changements trans-generationnels en reponse au stress incluent les modifications de la methylation d'ADN et les changements de frequence de recombinaison homologue (FRH). La progeniture de vegetaux qui ont ete stresses presente souvent des niveaux eleves de FRH de meme qu'une hypermethylation genomique, meme si les locus specifiques benefiques en situation de stress peuvent etre hypomethyles. Un des possibles mecanismes responsables du transfert de memoire a la progeniture implique les petits ARN interferents, les proteines de type DICER DCL2 et DCL3, qui sont en partie necessaire a ce processus. Cependant, alors que les modifications epigenetiques sont souvent presentes chez la progeniture non traitee de vegetaux stresses, elles ne sont habituellement pas durables pendant de multiples generations non exposees. Quoi qu'il en soit, l'heritabilite trans-generationnelle de tels changements a deja commence a fournir une preuve du role important de l'epigenetique dans l'augmentation de la resistance au stress. [Traduit par la Redaction] Mots-cles : recombinaison homologue, methylation d'ADN, reponse au stress chez les vegetaux, regulation epigenetique, effet trans-generationnel, evolution adaptative., Introduction Plants are an extremely important source of nutrition for our growing global population, and agriculture plays a key role in the economy of many countries. Because of their stationary [...]

Soybean (Glycine max (L.) Merr.) is an important crop that provides a sustainable source of protein and oil worldwide. Soybean cyst nematode (Heterodera glycines Ichinohe) is a microscopic roundworm that [...]

Among the arsenal of plant-derived compounds activated upon attack by herbivores and pathogens are small peptides that initiate and amplify defense responses. However, only a handful of plant signaling peptides have been reported. Here, we have isolated a 12-aa peptide from soybean (Glycine max) leaves that causes a pH increase of soybean suspension-cultured cell media within 10 min at low nanomolar concentrations, a response that is typical of other endogenous peptide elicitors and pathogen-derived elicitors. The amino acid sequence was determined and was found to be derived from a member of the subtilisin-like protease (subtilase) family. The sequence of the peptide was located within a region of the protein that is unique to subtilases in legume plants and not found within any other plant subtilases thus far identified. We have named this peptide signal Glycine max Subtilase Peptide (GmSubPep). The gene (Glyma18g48580) was expressed in all actively growing tissues of the soybean plant. Although transcription of Glyma18g48580 was not induced by wounding, methyl jasmonate, methyl salicylate, or ethephon, synthetic GmSubPep peptide, when supplied to soybean cultures, induced the expression of known defense-related genes, such as Cyp93A1, Chib-1b, PDR12, and achs. GmSubPep is a unique plant defense peptide signal, cryptically embedded within a plant protein with an independent metabolic role, providing insights into plant defense mechanisms. damaged-self recognition | plant defense | signaling peptide | subtilase doi/ 10.1073/pnas.1007568107

Host resistance is important to control Fusarium head blight (FHB)), caused by the fungus Fusarium graminearum (Schwabe) [teleomorph: Gibberella zeae (schw.) Petch], in wheat (Triticum aestivum L.). Effective breeding requires understanding the genetics of resistance in breeding populations. Our objective was to deduce the genetics of FHB resistance in eastern U.S. soft red winter wheat (SRWW) by estimating heritability, means, and phenotype frequencies. We evaluated the FHB index of 2983 lines from 223 parents in a series of single- and multiyear trials conducted in inoculated FHB nurseries. The mean index of all lines (23.8%) was similar to that of the moderate resistant check (19.7%), and the distribution was often skewed toward low index values. Without selection, 41% of all lines had moderate resistance and 70% of all crosses produced such lines. Entry-mean heritability for index generally exceeded 0.65 and selection for lower index reduced the index by -37%. The moderate resistance arose from many SRWW parents with varying levels of FHB resistance. The genetics of resistance in this population is probably characterized by a relatively high frequency of resistance alleles at multiple loci, dispersed over many parents that differ in allele content at loci controlling FHB resistance. This population should provide excellent gain from recurrent selection and complement current marker-assisted selection efforts. doi: 10.2135/cropsci2008.09.0569

Introduced plants tend to experience less herbivory than natives, although herbivore loads vary widely. Herbivores may switch hosts onto an introduced plant for at least two reasons. They may recognize the novel plant as a potential host based on similarity of the plant's traits to the traits of one of its native hosts, a similarity that may or may not exhibit phylogenetic signal. Alternatively, herbivores may feed optimally, assessing which introduced plants provide the best nutrition irrespective of similarity to native species. Here, we created a phylogeny of 57 oak (Quercus) taxa, which were grown outside of their ranges in a common botanical garden that contained one abundant native oak (Quercus lobata). We used the phylogeny to estimate the phylogenetic conservatism of herbivory by two feeding guilds of insects (leaf chewers and leaf miners) and 11 plant traits expected to affect herbivore performance. We found high phylogenetic signal in chewing damage but not mining damage and all traits except for leaf maturation time. Introduced oaks that are more closely related to the native oak received more chewing and mining damage than distantly related oaks, and introduced oaks that had greater overall similarity in leaf traits also received higher chewing damage but not mining damage. These results demonstrate that interactions between introduced plants and their herbivores are driven independently by traits that track plant phylogeny and leaf traits that likely affect herbivore performance. community phylogeny | enemy release | introduced | plant defense | Quercus doi/10.1073/pnas.0904867106

Molecular markers derived from resistance gene analogs of HcrVf2, the first apple resistance gene cloned, may pave the way to the cloning of additional apple scab resistance genes. The Malus xdomestica 'Florina' (Vf) bacterial artificial chromosome (BAC) genomic library was screened by hybridization using HcrVJ2 as a probe. Positive BAC clones were assembled into contigs and microsatellite markers developed from each contig mapped. Only linkage groups 1 and 6 contained HcrVJ2 paralogs. On linkage group 1, five loci in addition to the Vf locus were identified. A single locus was detected on linkage group 6. Representative BAC clones of these loci including the Vf locus were sequenced and the gene structure compiled. A total of 22 sequences, showing high sequence similarity to HcrVf2, were identified. Nine sequences were predicted to encode all seven protein domains described in HcrVf2, while three were truncated. Transcriptional analysis indicated that six genes with a complete HcrVf-like structure were constitutively expressed in young uninfected leaves of 'Florina'. The map position of each HcrVf analog was compared with the location of the major apple scab resistance genes. None of the major genes conferring scab resistance co-localized with HcrVf paralogs, indicating that they are unlikely to belong to the leucine-rich repeat--transmembrane class, which includes the Vf gene. Key words: gene-for-gene, receptor-like protein, apple scab, Venturia inaequalis, fungal-plant relationships. Des marqueurs moleculaires derives d'analogues du gene de resistance HcrVf2, le premier gene de resistance clone chez le pommier, pourraient paver la voie en vue du clonage d'autres genes de resistance a la tavelure du pommier. La banque genomique de clones BAC du Malus xdomestica 'Florina' (Vf) a ete criblee par hybridation en utilisant comme sonde HcrVf2. Des clones BAC positifs ont ete assembles en contigs, des marqueurs microsatellites ont ete developpes a partir de chaque contig et ces marqueurs ont ete cartographies. Seuls les groupes de liaison 1 et 6 portaient des paralogues de HcrVf2. Sur le groupe de liaison 1, cinq locus ont ete identifies en plus du locus Vf tandis qu'un seul locus a ete identifie sur le groupe de liaison 6. Des clones BAC representatifs de ces locus, incluant le locus Vf, ont ete sequences et la structure des genes a ete determinee. Au total, 22 sequences montrant une grande similarite avec la sequence de HcrVJ2 ont ete identifiees. Il a ete predit que neuf des sequences codaient pour l'ensemble des sept domaines proteiques decrits chez HcrVf2, tandis que trois etaient tronquees. Une analyse des transcrits a revele que les six genes affichant une structure intacte de type HcrVf etaient exprimes constitutivement chez de jeunes feuilles non-infectees du 'Florina'. La position sur la carte genetique de chaque analogue HcrVf a ete comparee a l'emplacement des principaux genes de resistance a la tavelure. Aucun des genes majeurs conferant la resistance a la tavelure ne co-localisait avec les paralogues HcrVf, ce qui indique qu'il est peu vraisemblable qu'ils fassent partie de la classe des LRR-TM, laquelle inclut le gene Vf. Mots-cles : gene-pour-gene, proteine de type recepteur, tavelure du pommier, Venturia inaequalis, relations plante-champignon., Introduction Apple scab, caused by the ascomycetes Venturia inaequalis, is the most important fungal pathogen of the cultivated apple Malus x domestics (MacHardy 1996). The pathogen undergoes a gene-for-gene relationship [...]

Fire blight, caused by the bacterium Erwinia amylovora, is one of the most destructive diseases of apple (Malus xdomestica) worldwide. No major, qualitative gene for resistance to this disease has been identified so far in apple. A quantitative trait locus (QTL) analysis was performed in two Fl progenies derived from two controled crosses: one between the susceptible rootstock cultivar 'MM106' and the resistant ornamental cultivar 'Evereste' and the other one between the moderately susceptible cultivar 'Golden Delicious' and the wild apple Malus floribunda clone 821, with unknown level of fire blight resistance. Both progenies were inoculated in the greenhouse with the same reference strain of E. amylovora. The length of stem necrosis was scored 7 and 14 days after inoculation. A strong QTL effect was identified in both 'Evereste' and M. floribunda 821 at a similar position on the distal region of linkage group 12 of the apple genome. From 50% to 70% of the phenotypic variation was explained by the QTL in 'Evereste' progeny according to the scored trait. More than 40% of the phenotypic variation was explained by the M. floribunda QTL in the second progeny. It was shown that 'Evereste' and M. floribunda 821 carried distinct QTL alleles at that genomic position. A small additional QTL was identified in 'Evereste' on linkage group 15, which explained about 6% of the phenotypic variation. Although it was not possible to confirm whether or not 'Evereste' and M. floribunda QTL belonged to the same locus or two distinct closely related loci, these QTL can be valuable targets in marker-assisted selection to obtain fire blight resistant apple cultivars and form a starting point for discovering the function of the genes controlling apple fire blight resistance. Key words: Malus xdomestica, Erwinia amylovora, fire blight, quantitative resistance loci, homology. Le feu bacterien, cause par la bacterie Erwinia amylovora, est une des maladies les plus destructives du ommier (Malus xdomestica) au niveau mondial. Aucun gene majeur, qualitatif, de resistance a cette maladie n'a ete identifie jusqu'a present. Une recherche de loci de caractere quantitatif (QTL : << quantitative trait locus >>) a ete realisee dans deux descendances [F.sub.1] issues de deux croisements controles : l'un entre le porte-greffe sensible 'MM106' et le cultivar ornemental 'Evereste' et l'autre entre le cultivar moyennement sensible 'Golden Delicious' et le clone 821 de pommier sauvage Malus floribunda, dont le niveau de resistance au feu bacterien n'etait pas encore connu. Les deux descendances ont ete inoculees en serre avec la meme souche de reference d'E. amylovora. La longueur de necrose sur la tige etait mesuree a 7 et 14 jours apres inoculation. Deux QTL a fort effet ont ete identifies chez 'Evereste' et M. floribunda 821 a une position similaire sur la region distale du groupe de liaison 12 du genome du pommier. Entre 50 % et 70 % de la variation phenotypique etait expliquee par le QTL dans la descendance issue d'Evereste' selon le caractere considere. Plus de 40 % de la variation phenotypique etait explique par le QTL de M. floribunda dans la seconde descendance. Nous avons montre que 'Evereste' et M. floribunda 821 portaient des alleles distincts aux QTL dans cette region genomique. Un QTL additionnel a faible effet a ete identifie chez 'Evereste' sur le groupe de liaison 15; il explique environ 6 % de la variation phenotypique. Bien qu'il n'ait pas ete possible de repondre a la question concernant l'existence d'un seul locus ou de deux loci etroitement lies chez 'Evereste' et M. floribunda, ces QTL sont des cibles interessantes a la fois pour la selection assistee par marqueurs dans l'optique de creer des cultivars resistants au feu bacterien et pour le clonage dans l'optique de decouvrir la fonction des genes controlant la resistance au feu bacterien. Mots-cles : Malus xdomestica, Erwinia amylovora, feu bacterien, locus de caractere quantitatif, homologie., Introduction Fire blight, caused by the necrogenic Gram-negative bacterium Erwinia amylovora, is one of the most destructive diseases of apple (Malus x domestics) and pear (Pyrus communis) worldwide. The number [...]

Many populations of goldenrod show a peculiar, genetically controlled stem dimorphism. In Solidago altissima, for instance, while most stems are erect, a sizable minority (the 'candy-cane' stems) nod at the apex during growth. We used data from three studies to test the hypothesis that this candy-cane growth form confers resistance to herbivory. In a controlled growth trial, we showed that nodding is a temporary phenomenon that coincides with the oviposition period of at least two common apex-attacking herbivores: the tephritid galler Eurosta solidaginis and the gall midge Rhopalomyia solidaginis. In a large field survey, stems of candy-cane genets were only half as likely to be ovipunctured by E. solidaginis. In a common-garden study, candy-cane stems were less likely to be ovipunctured by E. solidaginis, and they were galled only half as often by R. solidaginis as erect stems. These results suggest that the candy-cane stems of goldenrod possess a resistance strategy that allows them to essentially duck and hide from certain herbivores. Key words: candy-cane stems; ducking; Eurosta solidaginis; galls; goldenrod; resistance to herbivory; Rhopalomyia solidaginis; Solidago altissima; stem morphology.

As the basal resource in most food webs, plants have evolved myriad strategies to battle consumption by herbivores. Over the past 50 years, plant defense theories have been formulated to explain the remarkable variation in abundance, distribution, and diversity of secondary chemistry and other defensive traits. For example, classic theories of enemy-driven evolutionary dynamics have hypothesized that defensive traits escalate through the diversification process. Despite the fact that macro-evolutionary patterns are an explicit part of defense theories, phylogenetic analyses have not been previously attempted to disentangle specific predictions concerning (i) investment in resistance traits, (ii) recovery after damage, and (iii) plant growth rate. We constructed a molecular phylogeny of 38 species of milkweed and tested four major predictions of defense theory using maximum-likelihood methods. We did not find support for the growth-rate hypothesis. Our key finding was a pattern of phyletic decline in the three most potent resistance traits (cardenolides, latex, and trichomes) and an escalation of regrowth ability. Our neontological approach complements more common paleontological approaches to discover directional trends in the evolution of life and points to the importance of natural enemies in the macroevolution of species. The finding of macroevolutionary escalating regowth ability and declining resistance provides a window into the ongoing coevolutionary dynamics between plants and herbivores and suggests a revision of classic plant defense theory. Where plants are primarily consumed by specialist herbivores, regrowth (or tolerance) may be favored over resistance traits during the diversification process. cardenolides | coevolution | macroevolutionary trends | milkweed Asclepias | plant defense theory

Elevated levels of atmospheric carbon dioxide (C[O.sub.2]), a consequence of anthropogenic global change, can profoundly affect the interactions between crop plants and insect pests and may promote yet another form of global change: the rapid establishment of invasive species. Elevated C[O.sub.2] increased the susceptibility of soybean plants grown under field conditions to the invasive Japanese beetle (Popilliajaponica) and to a variant of western corn rootworm (Diabrotica virgifera virgifera) resistant to crop rotation by down-regulating gene expression related to defense signaling [lipoxygenase 7 (10x7), lipoxygenase 8 (10x8), and 1-aminocyclopropane-1-carboxylate synthase (acc-s)]. The down-regulation of these genes, in turn, reduced the production of cysteine proteinase inhibitors (CystPIs), which are specific deterrents to coleopteran herbivores. Beetle herbivory increased CystPI activity to a greater degree in plants grown under ambient than under elevated C[O.sub.2]. Gut cysteine proteinase activity was higher in beetles consuming foliage of soybeans grown under elevated C[O.sub.2] than in beetles consuming soybeans grown in ambient C[O.sub.2], consistent with enhanced growth and development of these beetles on plants grown in elevated C[O.sub.2]. These findings suggest that predicted increases in soybean productivity under projected elevated C[O.sub.2] levels may be reduced by increased susceptibility to invasive crop pests. Diabrotica virgifera | global change | Glycine max | plant-insect interactions | Popillia japonica

Before the Spanish conquest of the ancient Americas, the grain amaranths (Amaranthus caudatus L., A. cruentus L., A. hypochondriacus L.) were a staple food of the New World. Recently, the groin amaranths have regained international attention for their nutritional quality and importance as a symbol of indigenous cultures. Here we report the development of a bacteriol artificial chromosome (BAC) library constructed from the cultivar 'Plainsmon' (A. hypochondriacus; 2n = 2x = 32). The library consists of a total of 36,864 clones with an average insert size of 147 kb with less than 1.8% of the clones containing empty vectors. The frequency of BAC clones carrying inserts derived from chloroplast and mitochondrial DNA was estimated to be 6.9%. Thus, based on a haploid genome size of 466 Mb per haploid nucleus, the BAC library coverage is approximately 10.6 times the haploid genome content. The genome coverage estimate was empirically confirmed by screening the library with seven low copy amaranth probe sequences. The utility of the amaranth BAC library was demonstrated by identification and full-length genomic sequencing of the acetolactate syntbase and protoporphyrinogen oxidase genes--both major targets for several classes of important herbicides. The quality of the BAC library for BAC end sequencing projects was evaluated by bidirectional end sequencing of 384 random clones. End sequences were annotated using BLAST searches and queries to plant transposable element databases.

Defensins represent a diverse set of antimicrobial peptides found in almost all multicellular organisms. These small proteins can be characterized by an N-terminal signal sequence, a highly divergent mature protein with the exception of conserved cysteine residues, presence of defensin motifs, and a tissue-specific expression pattern. Defensin expression can be induced by pathogen inoculation and environmental stress. Until recently, defensins in plants were thought to be members of small gene families. However, the advent of expressed sequence tag (EST) and genome sequencing coupled with novel bioinformatic techniques has allowed researchers to recognize the size and diversity of the family. Recent research has identified over 300 defensin-like (DEFL) genes in each of the genomes of Arabidopsis thaliana (L.) Heynh. and Medicago truncatula Gaertner. In addition, over 1000 DEFL genes have been identified from the plant EST projects. The identification of such a broad family involved in defense against pathogens and environmental stress provides new opportunities for crop improvement. This review focuses on genome level analyses of DEFL genes in plants.

Theory predicts that bottom-up ecological forces can affect community dynamics, but whether this extends to the effects of heritable plant variation on tritrophic communities is poorly understood. In a field experiment, I contrasted the effects of plant genotype (28 genotypes; 1064 plants), aphid density, and the presence/absence of mutualistic ants in affecting the per capita population growth of a specialist aphid herbivore, as well as the effects of plant genotype on the third trophic level. Plant genotype strongly affected aphid population growth rate, explaining 29% of the total variation in growth rate, whereas aphid density and ant-aphid interactions explained substantially less variation (

Potatoes (Solanum tuberosum L.) and humans (Homo sapiens L.) are both outcrossing species. The phenotypic variation of both is controlled by environmental factors and by natural DNA polymorphisms between individuals. Therefore we adopt similar approaches as used in human population genetics, such as association mapping, to identify loci and their alleles that are causal for complex agronomic characters such as quantitative resistance to pathogens or tuber sugar content. Functional analysis of genes operating in resistance to pests and pathogens or n carbohydrate metabolism, either in potato itself or in other plants including the model species Arabidopsis thaliana (L.) Heynh., provides many functional candidates for these complex agronomic traits, n our approach functional candidate genes are tested for linkage to quantitative trait loci (QTL) for pathogen resistance or tuber quality traits, thereby selecting positional candidates (genes colocalizing with a QTL). DNA polymorphisms n or physically linked to positional candidate genes are then evaluated n populations of tetraploid potato genotypes and tested for association with phenotypes evaluated in the same populations. We have used the candidate gene approach to identify DNA-based markers that are diagnostic for quantitative resistance to late blight caused by Phytophthora infestans (Mont.) de Bary, to the root cyst nematode Globodera pallida (Stone), and for chip color in tetraploid potato cultivars and in advanced breeding clones.

Selection against pink stem borer (Sesamia non-agrioides Lef) (PSB) attack was performed in the maize (Zea mays L.) synthetic EPS12. The direct response of the EPS12 population to three cycles of selection to reduce tunnel length damage by PSB while maintaining yield was evaluated. [S.sub.0] (cycles of selection) and [S.sub.1] (selfed cycles of selection) generations and testcrosses to three testers were evaluated under artificial infestation with two corn borers, PSB and European corn borer (Ostrinia nubilalis Hubner) (ECB). Genotypes and the genotype x environment interaction were significant for tunnel length and yield. Differences among cycles of selection were significant for tunnel length, and the linear decrease for this trait (-1.80 cm [cycle.sup.1]) achieved during selection accounted for most of these differences. Yield was not significantly reduced with selection. Inbreeding for yield significantly increased due to selection. EPS12 crossed to EP42 showed a significant increase in yield with selection, while crosses to other testers showed a nonsignificant reduction in yield. Although crosses to EP42 were not significantly different for tunnel length, the high heterosis between EPS12 and EP42 and the increased yield of EPS12 x EP42 during selection suggest that inbred lines developed from advanced cycles of EPS12 could be crossed to EP42 to generate promising hybrids. In general, resistance to PSB and ECB was improved, while yield was maintained, inbreeding was increased, and yield of the cross EP42 x EPS12 was improved.

Maize (Zea mays L.) production in west and central Africa (WCA) is constrained by the parasitic weed Striga hermonthica (Del.) Benth and recurrent drought. Two early maize populations, TZE-W Pop DT STR [C.sub.0] (white) and TZE-Y Pop DT STR [C.sub.0] (yellow), developed from diverse genetic backgrounds, were subjected to three cycles of [S.sub.1] recurrent selection under artificial Striga infestation. Inbreds and synthetic cultivars were developed from the different cycles of selection. The populations ([C.sub.0]), derived cultivars, and check cultivars were evaluated in 2002 and 2003 under Striga-infested and Striga-free environments in WCA. The objective was to assess the performance of the derived cultivars from the different cycles of selection. Under Striga infestation, ACR 94 TZE Comp5-Y and ACR 94 TZE Comp5-W, which were not from the selection program, were the highest-yielding group (2158 and 2124 kg [ha.sup.-1], respectively). The second group comprised six products of the selection program, with grain yield ranging from 1806 to 1954 kg [ha.sup.-1]. The third group, with grain yield of 1498 to 1759 kg [ha.sup.-1] contained mostly Striga-susceptible cultivars and the Co of the selection program. Under Striga-free conditions, the performance of several cultivars from the selection program was equal to or better than ACR 94 TZE Comp5-Y and ACR 94 TZE Comp5-W. The genotype plus genotype x environment interaction biplot analysis demonstrated that EV DT-Y 2000 STR [C.sup.1] and TZE-W Pop DT STR [C.sub.3] from the selection program, along with ACR 94 TZE Comp5-W, had stable grain yield under Striga-infested and noninfested conditions.

The molecular nature of many plant disease resistance (R) genes is known; the largest class encodes nucleotide-binding site-leucinerich repeat (NBS-LRR) proteins that are structurally related to proteins involved in innate immunity in animals. Few genes conferring disease susceptibility, on the other hand, have been identified. Recent identification of susceptibility to the fungus Cochliobolus victoriae in Arabidopsis thaliana has enabled our cloning of LOV1, a disease susceptibility gene that, paradoxically, is a member of the NBS-LRR resistance gene family. We found LOV1 mediates responses associated with defense, but mutations in known defense response pathways do not prevent susceptibility to C. victoriae. These findings demonstrate that NBS-LRR genes can condition disease susceptibility and resistance and may have implications for R gene deployment. Cochliobolus victoriae | disease susceptibility | nucleotide binding site-leucine-rich repeat | victorin

The tomato Tm-1 gene confers resistance to tomato mosaic virus (ToMV). Here, we report that the extracts of Tm-1 tomato cells (GCR237) have properties that inhibit the in vitro RNA replication of WT ToMV more strongly than that of the Tm-1-resistance-breaking mutant of ToMV, LT1. We purified this inhibitory activity and identified a polypeptide of [approximately equal to] 80 kDa ([p80.sup.GCR237]) using LC-tandem MS. The amino acid sequence of [p80.sup.GCR237] had no similarity to any characterized proteins. The [p80.sup.GCR237] gene cosegregated with Tm-1; transgenic expression of [p80.sup.GCR237] conferred resistance to ToMV within tomato plants; and the knockdown of [p.sup.80.GCR237] sensitized Tm-1 tomato plants to ToMV, indicating that Tm-1 encodes [p80.sup.GCR237] itself. We further show that in vitro-synthesized Tm-1 ([p80.sup.GCR237]) protein binds to the replication proteins of WT ToMV and inhibits their function at a step before, but not after, the viral replication complex is formed on the membrane surfaces. Such binding was not observed for the replication proteins of LT1. These results suggest that Tm-1 ([p80.sup.GCR237]) inhibits the replication of WT ToMV RNA through binding to the replication proteins. Tm-1 | Tomato mosaic virus | inhibitory interaction

Systemin is a wound-signaling peptide that mediates defenses of tomato plants against herbivorous insects. Perception of systemin by the membrane-bound receptor SR160 results in activation of MAPKs, synthesis of jasmonic acid (JA), and expression of defense genes. To test the function of MAPKs in the response to systemin, we used virus-induced gene silencing (VIGS) in plants that over-express the systemin precursor prosystemin (35S::prosys plants). These transgenic plants accumulate high levels of defense proteins and exhibit increased resistance to herbivorous insects. Cosilencing of the MAPKs MPK1 and MPK2 reduced MPK1/2 kinase activity, JA biosynthesis, and expression of JA-dependent defense genes. Application of methyI-JA restored the full defense response. These data show that MPK1 and MPK2 are essential components of the systemin signaling pathway and most likely function upstream of JA biosynthesis. MPK1 and MPK2 are 95% identical at the amino acid level. Specific VIGS of only MPK1 or MPK2 resulted in the same reduction of defense gene expression as cosilencing of MPK1 and MPK2, indicating that gene dosage effects may be important for MPK signaling. In addition, VIGS of the closely related MPK3 also reduced systemin-induced defense responses. The function of MPK1/2 and orthologs in pathogen-induced defenses is well established. Here we show that cosilencing of MPK1 and MPK2 compromised prosystemin-mediated resistance to Manduca sexta (Lepidoptera) herbivory, demonstrating that MPK1 and MPK2 are also required for successful defenses against herbivorous insects. jasmonic acid | plant-insect interactions | virus-induced gene silencing

Abstract: Using a complementary (c)DNA-amplified fragment length polymorphism (AFLP) approach, we investigated differential gene expression linked to resistance mechanisms during the incompatible potato--Globodera pallida interaction. Expression was compared between a [...]

Optimal defense theories suggest that a trade-off between defense costs and benefits maintains genetic variation within plant populations. This study assessed the independent and interactive effects of genetic- and environment-based variation in aspen leaf chemistry on insect performance, preference, and defoliation. Gypsy moth larvae were released into screenhouses containing eight aspen genotypes growing with high and low levels of nutrient availability. Plant chemistry, defoliation, and larval growth rates varied in response to genotype, nutrient availability, and their interaction. Total phenolic glycoside concentrations were inversely correlated with patterns of larval preference and were the best predictor of larval performance and defoliation among genotypes. Low-nutrient trees were less heavily defoliated and afforded decreased larval growth rates compared with high-nutrient trees. Nutrient availability mediated the defense benefits of phenolic glycosides, as plant chemistry explained significantly less variation in defoliation in low- compared with high-nutrient trees (7% vs. 44% of variation explained). These results suggest that spatial and temporal variation in resource availability may influence the relative magnitude of defense benefits in plants. Environmental mediation of the defense costs and benefits likely leads to diversifying selection and may maintain genetic polymorphisms in chemical defense traits in plant populations. Key words: chemical defense; genetic variation; gypsy moth; Lymantria dispar; mesocosms; plant defense; Populus tremuloides; preference.

Wild barley (Hordeum spontaneum) represents a significant genetic resource for crop improvement in barley (Hordeum vulgare) and for the study of the evolution and domestication of plant populations. The Isa gene from barley has a putative role in plant defense. This gene encodes a bifunctional [alpha]-amylase/subtilisin inhibitor that inhibits the bacterial serine protease subtilisin, fungal xylanase, and the plant's own [alpha]-amylase. The inhibition of plant [alpha]-amylases suggests this protein may also be important for grain quality from a human perspective. We identified 16 SNPs in the coding region of the Isa locus of 178 wild barley accessions from eight climatically divergent sites across Israel. The pattern of SNPs suggested a large number of recombination events within this gene, indicating that the Iow-outcrossing rate of wild barley is not a barrier to recombinant haplotypes becoming established in the population. Seven amino acid substitutions were present in the coding region. Genetic diversity for each population was calculated by using Nei's diversity index, and a Spearman rank correlation was carried out to test the association between gene diversity and 16 ecogeographical factors. Highly significant correlations were found between diversity at the Isa locus and key water variables, evaporation, rainfall, humidity, and latitude. The pattern of association suggests selective sweeps in the wetter climates, with resulting low diversity and weaker selection or diversifying selection in the dryer climates resulting in much higher diversity. climatic selection | crop improvement | Hordeum spontaneum | Isa molecular polymorphism

Predictions based on the plant age and growth-differentiation balance hypotheses of defense were tested in two congeneric species, Plantago laceolata and P. major, by quantifying iridoid glycosides, defensive chemicals, in seeds and leaves during the first 6 wk of growth. Concentrations decreased from the seed to 2-wk-old seedling stage in P. lanceolata, but increased during this period in P. major. In both species, levels were similar for 2- and 4-wk-old plants, then significantly increased from 4 to 6 wk. Genetic variation in the ontogeny of iridoid glycoside production was significant in both species at the maternal family level and at the population level. To examine whether allocation costs could explain the low production of iridoid glycosides in seedlings, relationships between growth and defense (iridoid glycosides) were characterized. Growth and defense had a positive or null relationship in all age groups, indicating that there was no trade-off in these plants at any age. This study provides some support for the growth--differentiation balance hypothesis, but otters no support for the plant age hypothesis. Measuring how herbivory affects plant fitness at different ontogenetic stages may shed light on these patterns in Plantago and on the evolution of the ontogeny of defense. Key words: allocation constraints; growth defense trade-offs; iridoid glycosides; ontogenetic drift; plant age; Plantaginaceae; secondary chemistry; seedling.