Plant Bio-Wars: Maize Protein Networks Reveal Tissue-Specific Defense Strategies in Response to a Root Herbivore.

In this study we examined global changes in protein expression in both roots and leaves of maize plants attacked by the root herbivore, Western corn rootworm (WCR, Diabrotica virgifera virgifera). The changes in protein expression Are indicative of metabolic changes during WCR feeding that enable the plant to defend itself. This is one of the first studies to look above- and below-ground at global protein expression patterns of maize plants grown in soil and infested with a root herbivore. We used advanced proteomic and network analyses to identify metabolic pathways that contribute to global defenses deployed by the insect resistant maize genotype, Mp708, infested with WCR. Using proteomic analysis, 4878 proteins in roots and leaves were detected and of these 863 showed significant changes of abundance during WCR infestation. Protein abundance patterns were analyzed using hierarchical clustering, protein correlation and protein-protein interaction networks. All three data analysis pipelines showed that proteins such as jasmonic acid biosynthetic enzymes, serine proteases, protease inhibitors, proteins involved in biosynthesis and signaling of ethylene, and enzymes producing reactive oxygen species and isopentenyl pyrophosphate, a precursor for volatile production, were upregulated in roots during WCR infestation. In leaves, highly abundant proteins were involved in signal perception suggesting activation of systemic signaling. We conclude that these protein networks contribute to the overall herbivore defense mechanisms in Mp708. Because the plants were grown in potting mix and not sterilized sand, we found that both microbial and insect defense-related proteins were present in the roots. The presence of the high constitutive levels of reduced ascorbate in roots and benzothiazole in the root volatile profiles suggest a tight tri-trophic interaction among the plant, soil microbiomes and WCR-infested roots suggesting that defenses against insects coexist with defenses against bacteria and fungi due to the interaction between roots and soil microbiota. In this study, which is one of the most complete descriptions of plant responses to root-feeding herbivore, we established an analysis pipeline for proteomics data that includes network biology that can be used with different types of "omics" data from a variety of organisms.

Susceptibility of wounded and intact black soldier fly Hermetia illucens (L.) (Diptera: Stratiomyidae) to entomopathogenic nematodes.

Production costs and limited regional availability are two key factors limiting the widespread adoption of entomopathogenic nematodes (Rhabditida: Heterorhabditidae and Steinernematidae) in biological control programs. We explore the potential of using black soldier fly larvae Hermetia illucens (L.) (Diptera: Stratiomyidae) as an alternative in vivo rearing host to the greater wax moth, Galleria mellonella (L.) (Lepidoptera: Pyralidae). We injured black soldier fly larvae to test the hypothesis that the tough cuticle was preventing the penetration of founding infective juveniles (IJs) into the host and egress of offspring from the cadaver. Injuring the black soldier fly larvae increased the infection rate, the number of nematodes entering a host, and the number of IJs harvested from a cadaver. Black soldier fly larvae, however, provided at most 10-fold less IJs compared to G. mellonella. In olfactometer assays, we assessed nematode behavioral responses to wounded black soldier fly larvae. Steinernema carpocapsae did not move towards the insects. Heterorhabditis bacteriophora was attracted to black soldier fly larvae but not G. mellonella. Heterorhabditis bacteriophora did not show a preference for injured black soldier fly larvae over non-injured larvae. Thus, increased colonization on wounded black soldier fly larvae was likely due to additional entry points rather than an increase in their apparency in the soil solution.

Ecology and evolution of soil nematode chemotaxis.

Plants influence the behavior of and modify community composition of soil-dwelling organisms through the exudation of organic molecules. Given the chemical complexity of the soil matrix, soil-dwelling organisms have evolved the ability to detect and respond to these cues for successful foraging. A key question is how specific these responses are and how they may evolve. Here, we review and discuss the ecology and evolution of chemotaxis of soil nematodes. Soil nematodes are a group of diverse functional and taxonomic types, which may reveal a variety of responses. We predicted that nematodes of different feeding guilds use host-specific cues for chemotaxis. However, the examination of a comprehensive nematode phylogeny revealed that distantly related nematodes, and nematodes from different feeding guilds, can exploit the same signals for positive orientation. Carbon dioxide (CO(2)), which is ubiquitous in soil and indicates biological activity, is widely used as such a cue. The use of the same signals by a variety of species and species groups suggests that parts of the chemo-sensory machinery have remained highly conserved during the radiation of nematodes. However, besides CO(2), many other chemical compounds, belonging to different chemical classes, have been shown to induce chemotaxis in nematodes. Plants surrounded by a complex nematode community, including beneficial entomopathogenic nematodes, plant-parasitic nematodes, as well as microbial feeders, are thus under diffuse selection for producing specific molecules in the rhizosphere that maximize their fitness. However, it is largely unknown how selection may operate and how belowground signaling may evolve. Given the paucity of data for certain groups of nematodes, future work is needed to better understand the evolutionary mechanisms of communication between plant roots and soil biota.