A novel impact of a novel weapon: allelochemicals in Alliaria petiolata disrupt the legume-rhizobia mutualism

Cyclic Isothiocyanate Goitrin Impairs Lotus japonicus Nodulation, Affects the Proteomes of Nodules and Free Mesorhizobium loti, and Induces the Formation of Caffeic Acid Derivatives in Bacterial Cultures

The continuous release of glucosinolates into the soil by Brassicaceae root exudation is a prerequisite to maintaining toxic levels of breakdown products such as isothiocyanates (ITCs). ITCs influence plant and microbial diversity in ecosystems, while fungi and Rhizobiaceae are particularly injured. Studies explaining the molecular mechanisms of the negative effects are presently limited. Therefore, we investigated the early effects of cyclic ITC goitrin on proteomes of the host and symbiotic Mesorhizobium loti in the nodules of Lotus japonicus and of free-living bacteria. In the nodules, many host proteins had a higher abundance, among them, peroxidases and pathogenesis-related PR-10 proteins functioning in the abscisic-acid-activated signaling pathway. In the microsymbiont, transporter proteins as a prominent group are enhanced; some proteins involved in N-fixation decreased. The proteomes give a report about the loss of immunity suppression resulting in the termination of symbiosis, which initiates nodule senescence. Free-living M. loti are severely damaged, indicated, i.a., by a decrease in transporter proteins, the assumed candidates for goitrin protein complex formation, and high proteolysis. The production of chicoric acid by the accompanying bacteria is inhibitory for M. loti but connected to goitrin elimination, as confirmed by mass spectrometric (MS) analysis. In summary, the nodulation process is severely affected by goitrin, causing nodule dysfunction and failed nodule development. N deficiency conditions leads to yellowish leaves and leaf abscission.

OUP accepted manuscript

The invasive plant Alliaria petiolata (garlic mustard) has spread throughout forest understory and edge communities in much of North America, but its persistence, density, and impacts have varied across sites and time. Surveying the literature since 2008, we evaluated both previously proposed and new mechanisms for garlic mustard's invasion success and note how they interact and vary across ecological contexts. We analyzed how and where garlic mustard has been studied and found a lack of multisite and longitudinal studies, as well as regions that may be under- or overstudied, leading to poor representation for understanding and predicting future invasion dynamics. Inconsistencies in how sampling units are scaled and defined can also hamper our understanding of invasive species. We present new conceptual models for garlic mustard invasion from a macrosystems perspective, emphasizing the importance of synergies and feedbacks among mechanisms across spatial and temporal scales to produce variable ecological contexts.

[Responses of the common bean (Phaseolus vulgaris L.) and Rhizobium tropici CIAT899 symbiosystem to induced allelopathy by Ipomoea purpurea L. Roth]

Allelopathy is a phenomenon that involves the production of secondary metabolites that influence the growth of plants and microorganisms; however, this alellopathic effect has been scarcely studied on the rhizobia-legume symbiosis. The aims of this research were 1) to assess the allelopathic potential of aqueous extracts of Ipomoea purpurea L. Roth on seed germination and root length of common bean seedlings (Phaseolus vulgaris L.), 2) to determine its effects on the in vitro growth of Rhizobium tropici CIAT899, and 3) to evaluate the allelopathic potential of I. purpurea on the growth, nodulation and physiology of common bean plants inoculated with R. tropici. After 48h, 15% of the aqueous root extract of I. purpurea stimulated seed germination, whereas 4% of the aqueous shoot extracts stimulated such germination. Both the root or shoot extracts stimulated seed germination and e root length. In vitro growth of R. tropici was inhibited as a result of the application of both aqueous extracts. The presence of I. purpurea negatively affected both the growth and physiological responses of common bean plants, and this effect was attenuated after the inoculation of R. tropici; nevertheless, this allelopathic plant affected root nodulation. Our results suggest that the symbiosis of rhizobia and roots of common bean plants is an important element for attenuating the negative effects caused by the allelopathic plant.