Induced epidermal permeability modulates resistance and susceptibility of wheat seedlings to herbivory by Hessian fly larvae

Abstract

Salivary secretions of neonate Hessian fly larvae initiate a two-way exchange of molecules with their wheat host. Changes in properties of the leaf surface allow larval effectors to enter the plant where they trigger plant processes leading to resistance and delivery of defence molecules, or susceptibility and delivery of nutrients. To increase understanding of the host plant's response, the timing and characteristics of the induced epidermal permeability were investigated. Resistant plant permeability was transient and limited in area, persisting just long enough to deliver defence molecules before gene expression and permeability reverted to pre-infestation levels. The abundance of transcripts for GDSL-motif lipase/hydrolase, thought to contribute to cuticle reorganization and increased permeability, followed the same temporal profile as permeability in resistant plants. In contrast, susceptible plants continued to increase in permeability over time until the entire crown of the plant became a nutrient sink. Permeability increased with higher infestation levels in susceptible but not in resistant plants. The ramifications of induced plant permeability on Hessian fly populations are discussed.

Entomopathogenic fungi as potential biocontrol agents of the ecto-parasitic mite, Varroa destructor, and their effect on the immune response of honey bees (Apis mellifera L.)

“…The down regulation of gene expression for hymenoptaecin and pUf68 in brood infested only with V. destructor in this study, indicates that suppression of honey bee gene expression could be a result of varroa effector-triggered susceptibility (ETS). This could be similar to ETS resulting from putative effectors in the larval salivary secretions of the Hessian fly (Mayetiola destructor) that down regulates host genes and induces susceptibility in wheat, thus increasing production of plant nutrients for the larvae (Williams et al, 2011). Other studies have also shown that parasitism by varroa mites suppressed genes for antimicrobial peptides, such as abaecin and defensin, as well as genes for phenoloxidase, glucose dehydrogenase, glucose oxidase and lysozyme, which are all defense-related enzymes (Gregory et al, 2005;Yang and Cox-Foster, 2005;Navajas et al, 2008).…”

Flexible resource allocation during plant defense responses

“…The development of strong, competing sinks is the basis of the negative impacts on wheat and rice growth by the galling pests, Hessian fly and rice gall midge (Harris et al, 2006; Williams et al, 2011). Sink creation is widespread among galling insect species (Bronner, 1992) and has been shown for free living insect herbivores as well; it should be regarded as an important element of the impact insects can have on their host plants as well as on each other (Baldwin and Preston, 1999; Allison and Schultz, 2005).…”

Avirulence gene mapping in the Hessian fly (Mayetiola destructor) reveals a protein phosphatase 2C effector gene family

“…The first-instar larval offspring of the surviving females were then collected individually in 10 µL drops of water containing 0.02% NP-40 and placed, one larva per plant, on the youngest leaf of single H24-seedlings. Using a single larva per plant insures that avirulent larvae, which can survive on the nutritive tissue created by a virulent larva on the same plant (Harris et al, 2006, Williams et al, 2011, are eliminated from the population. Larvae that survived alone on the H24 seedlings were used to establish the H24-virulent strain.…”

“…The plant acts as the source of photosynthates and other nutrients and the developing HF larvae act as the sink that receives those substances (Harris et al, 2015, Stuart et al, 2012. In only 4 days, a single larva (<1 mm in length), secretes powerful substances that permanently cause the entire seedling to cease cell elongation, stop cell division, dramatically alter plant metabolism and severely increase cell permeability; all for the benefit of the larva (Liu et al, 2007, Stuart et al, 2012, Williams et al, 2011, Zhu et al, 2008. Increasing the expression of at least one wheat gene, Md susceptibility-1 (Mds-1), is critical to larval survival and plant stunting (Liu et al, 2013).…”