Volatile-Mediated Induced and Passively Acquired Resistance in Sagebrush (Artemisia tridentata).

Plants produce a diversity of secondary metabolites including volatile organic compounds. Some species show discrete variation in these volatile compounds such that individuals within a population can be grouped into distinct chemotypes. A few studies reported that volatile-mediated induced resistance is more effective between plants belonging to the same chemotype and that chemotypes are heritable. The authors concluded that the ability of plants to differentially respond to cues from related individuals that share the same chemotype is a form of kin recognition. These studies assumed plants were actively responding but did not test the mechanism of resistance. A similar result was possible through the passive adsorption and reemission of repellent or toxic VOCs by plants exposed to damage-induced plant volatiles (DIPVs). Here we conducted exposure experiments with five chemotypes of sagebrush in growth chambers; undamaged receiver plants were exposed to either filtered air or DIPVs from mechanically wounded branches. Receiver plants exposed to DIPVs experienced less herbivore damage, which was correlated with increased expression of genes involved in plant defense as well as increased emission of repellent VOCs. Plants belonging to two of the five chemotypes exhibited stronger resistance when exposed to DIPVs from plants of the same chemotypes compared to when DIPVs were from plants of a different chemotype. Moreover, some plants passively absorbed DIPVs and reemitted them, potentially conferring associational resistance. These findings support previous work demonstrating that sagebrush plants actively responded to alarm cues and that the strength of their response was dependent on the chemotypes of the plants involved. This study provides further support for kin recognition in plants but also identified volatile-mediated associational resistance as a passively acquired additional defense mechanism in sagebrush.

Small-secreted proteins as virulence factors in nematode-trapping fungi.

Nematode-trapping fungi (NTF), such as Arthrobotrys flagrans (Duddingtonia flagrans), are soil-borne fungi able to form adhesive trapping networks to attract and catch nematodes. In this forum piece we highlight some of their most fascinating features with a special focus on the role of small-secreted proteins in the predatory interaction.

Host and Pathogen Communication in the Respiratory Tract: Mechanisms and Models of a Complex Signaling Microenvironment.

Chronic lung diseases are a leading cause of morbidity and mortality across the globe, encompassing a diverse range of conditions from infections with pathogenic microorganisms to underlying genetic disorders. The respiratory tract represents an active interface with the external environment having the primary immune function of resisting pathogen intrusion and maintaining homeostasis in response to the myriad of stimuli encountered within its microenvironment. To perform these vital functions and prevent lung disorders, a chemical and biological cross-talk occurs in the complex milieu of the lung that mediates and regulates the numerous cellular processes contributing to lung health. In this review, we will focus on the role of cross-talk in chronic lung infections, and discuss how different cell types and signaling pathways contribute to the chronicity of infection(s) and prevent effective immune clearance of pathogens. In the lung microenvironment, pathogens have developed the capacity to evade mucosal immunity using different mechanisms or virulence factors, leading to colonization and infection of the host; such mechanisms include the release of soluble and volatile factors, as well as contact dependent (juxtracrine) interactions. We explore the diverse modes of communication between the host and pathogen in the lung tissue milieu in the context of chronic lung infections. Lastly, we review current methods and approaches used to model and study these host-pathogen interactions in vitro, and the role of these technological platforms in advancing our knowledge about chronic lung diseases.

Why do distance limitations exist on plant-plant signaling via airborne volatiles?

Plant volatiles are known to mediate many important ecological interactions between plants and insects. Plants themselves have also been shown to perceive volatile signals, but the short transmission distances documented thus far in nature raise questions about the ecological significance of plant-to-plant signaling. Recently, we reported that herbivore-induced plant volatiles (HIPVs) can function within an individual plant to overcome vascular constraints on systemic wound signaling. Within-plant signaling is consistent with the limited distances over which HIPVs have been shown to be perceived by plants. However, it remains unclear why these distance limitations should exist. Such limitations cannot be explained by volatile transport distance alone, since parasitoids respond to HIPVs over much greater distances. Thus, we suggest that the apparent distance limitations on plant-to-plant volatile signaling may arise from the mechanisms by which volatile signals are received by plants. These limitations may reflect physiological constraints on plants' ability to perceive volatiles or an adaptive mechanism to avoid responding to signals from other plants. Distinguishing between these possibilities will require additional research into the mechanisms of signal reception, about which little is currently known. Deciphering the ecological significance of HIPVs as phytohormones depends on understanding the mechanisms of HIPV reception.