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Western hemlock (Tsuga heterophylla) is highly susceptible to Annosus root and butt rot disease, caused by Heterobasidion occidentale across its native range in western North America. Understanding molecular mechanisms of tree defense and dissecting genetic components underlying disease resistance will facilitate forest breeding and disease control management. The aim of this study was to profile host transcriptome reprogramming in response to pathogen infection using RNA-seq analysis. Inoculated seedlings were clearly grouped into three types: quantitative resistant (QR), susceptible (Sus), and un-infected (Uif), based on profiles of H. occidentale genes expressed in host tissues. Following de novo assembly of a western hemlock reference transcriptome with more than 33,000 expressed genes, the defensive transcriptome reprogramming was characterized and a set of differentially expressed genes (DEGs) were identified with gene ontology (GO) annotation. The QR seedlings showed controlled and coordinated molecular defenses against biotic stressors with enhanced biosynthesis of terpenoids, cinnamic acids, and other secondary metabolites. The Sus seedlings showed defense responses to abiotic stimuli with a few biological processes enhanced (such as DNA replication and cell wall organization), while others were suppressed (such as killing of cells of other organism). Furthermore, non-synonymous single nucleotide polymorphisms (ns-SNPs) of the defense- and resistance-related genes were characterized with high genetic variability. Both phylogenetic analysis and principal coordinate analysis (PCoA) revealed distinct evolutionary distances among the samples. The QR and Sus seedlings were well separated and grouped into different phylogenetic clades. This study provides initial insight into molecular defense and genetic components of western hemlock resistance against the Annosus root and butt rot disease. Identification of a large number of genes and their DNA variations with annotated functions in plant resistance and defense promotes the development of genomics-based breeding strategies for improved western hemlock resistance to H. occidentale. [ABSTRACT FROM AUTHOR]

Garlic mustard is a well-known invader of deciduous forests of North America, yet the influence of environmental factors on garlic mustard allelochemical production is not well understood. Three experiments were conducted to detect interactions between one garlic mustard allelochemical (glucosinolate) production and light availability. First, to detect patterns of glucosinolate production across a natural light gradient, leaves and roots of mature plants and first-year rosettes were sampled in patches ranging from 100 to 2 % of full sun within an Indiana forest. Second, to determine whether genetic variation drives observed correlations between glucosinolate content and light, seed collected across light gradients within six sites was grown in a common garden and glucosinolate production was measured. Finally, to understand whether local adaptation occurred in garlic mustard's response to light, seed collected from defined light environments across six sites was grown under four light treatments. Results of the field sampling showed that mature plants' root glucosinolate content was elevated in high compared to low light. In the common garden experiment, however, there was no correlation between light availability at seed origin and constitutive glucosinolate content. Additionally, in the common light treatments, there was no evidence for local adaptation to light environment. Overall, the results indicate that plasticity in response to light, not genetic variation among plants growing in different light environments, generates correlations between glucosinolate content and light in the field. Since mature garlic mustard populations in high light may exhibit increased glucosinolate content, it makes them potential targets for management. [ABSTRACT FROM AUTHOR]

Abstract: Ethnopharmacological relevance: Cardamine diphylla (Michx.) A. Wood, commonly called toothwort, is a spring perennial herb belonging to the Brassicaceae family. This endemic plant of Eastern North America has been widely used by multiple American First Nations (i.e. indigenous people of North America) for food and medicine for centuries. Approach and methods: The aim of the review is to describe the botany, ethnopharmacology, phytochemistry, and bioactivity of Cardamine diphylla. The review covers literature on Cardamine diphylla, and the alternative name Dentaria diphylla, from English and French language sources. Results: Multiple traditional uses of Cardamine diphylla by American First Nations are well documented. Initial health studies showed that the tested concentrations of the extract were not toxic against brine shrimp larvae and the same extract had a weak free-radical scavenging activity. However, bioactive compounds in the form of aliphatic and indole glucosinolates and some indole alkaloids have been isolated from this plant. Ecological research regarding Cardamine diphylla-insect interactions (such as feeding and oviposition) is also available in the literature. Conclusions: The wide range of traditional uses by multiple American First Nations suggests that the antibacterial, antiviral, immunostimulant, analgesic, antipyretic, and anti-inflammatory activities of this plant should be explored in in vitro and in vivo tests. Traditional modes of preparation of the plant suggest that some of the medicinal properties could certainly be attributed to glucosinolate degradation products (i.e. isothiocyanates), but a clear assignment of active molecules and mechanisms of action remain to be elucidated. The presence of glucosinolates indicates that the plant could be probed for cancer chemopreventive properties. Overall, the review shows that more investigation is necessary to determine the possible benefits of Cardamine diphylla extracts to pharmaceutical companies as a nutraceutic specialty phytotherapeutic agent against respiratory (cold and sore throat) or gastrointestinal problems. [Copyright &y& Elsevier]

In the Brassicaceae, glucosinolates influence the feeding, reproduction and development of many insect herbivores. Glucosinolate production and effects on herbivore feeding have been extensively studied in the model species, Arabidopsis thaliana and Brassica crops, both of which constitutively produce leaf glucosinolates mostly derived from the amino acid, methionine. Much less is known about the regulation or role in defense of glucosinolates derived from other aliphatic amino acids, such as the branched-chain amino acids (BCAA), valine and isoleucine. We have identified a glucosinolate polymorphism in Boechera stricta controlling the allocation to BCAA- vs methionine-derived glucosinolates in both leaves and seeds. B. stricta is a perennial species that grows in mostly undisturbed habitats of western North America. We have measured glucosinolate profiles and concentrations in 192 F2 lines that have earlier been used for genetic map construction. We also performed herbivory assays on six F3 replicates per F2 line using the generalist lepidopteran, Trichoplusia ni. Quantitative trait locus (QTL) analysis identified a single locus controlling both glucosinolate profile and levels of herbivory, the branched chain-methionine allocation or BCMA QTL. We have delimited this QTL to a small genomic region with a 1.0 LOD confidence interval just 1.9 cm wide, which, in A. thaliana, contains ∼100 genes. We also found that methionine-derived glucosinolates provided significantly greater defense than the BCAA-derived glucosinolates against feeding by this generalist insect herbivore. The future positional cloning of this locus will allow for testing various adaptive explanations.Heredity (2009) 102, 465–474; doi:10.1038/hdy.2009.12; published online 25 February 2009 [ABSTRACT FROM AUTHOR]

Garlic mustard (Alliaria petiolata) is a nonnative, shade-tolerant forb that was introduced into North America in the mid-1800s. Currently, garlic mustard is spreading across the landscape at a rate of 6400 square kilometers per year. In this article, we synthesize the current state of knowledge on the mechanisms underlying garlic mustard's widespread success and the ecological impacts of its invasion. Although no single mechanism appears to explain the success of garlic mustard, a combination of plant traits--all slightly different from those of native plants--seems to confer garlic mustard with tremendous success in the new habitats it invades. The domination of this new species in eastern forests is clearly changing the ecology of these systems. The consequences of garlic mustard invasion include the loss of biological diversity, ripple effects through higher trophic levels, and changes in the function of soil microbial communities. [ABSTRACT FROM AUTHOR]