ARS | Publication request: Plant responses to hidden herbivores: European corn borer (ECB; Ostrinia nubilalis) attack on maize induces both defense and susceptibility

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 4, 2012
Publication Date: N/A

Technical Abstract: Herbivore-induced plant defenses have been widely described following attack on leaves; however, less attention has been paid to analogous local processes that occur in stems or roots. Early attempts to characterize maize responses to stem boring by European corn borer (ECB; Ostrinia nubilalis) larvae revealed the presence of inducible acidic diterpenoid phytoalexins, termed kauralexins, and increases in the benzoxazinoid 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one-glucose (HDMBOA-glc). Despite these rapidly activated defenses, larval growth was not significantly altered in short-term feeding assays. Unexpectedly, ECB growth assays conducted after 2 days of stem attack revealed significantly improved larval growth on previously challenged tissues. Correspondingly, measures of total soluble protein revealed 2.6-fold increases in ECB challenged stems and also elevated levels of sucrose and free linoleic acid. While microarray analyses detected up-regulation of over 1100 transcripts, very few individual protein increases were demonstrable from conservative iTRAQ estimates. Consistent with induced endoreduplication, both wounding and ECB stem attack resulted in significant expansion of cell nuclei, nucleoli and levels of extractable DNA from challenged tissues. The heightened defense and housekeeping-related metabolic demands of the ECB attacked tissue are likely to cause modest increases in much of the plant proteome. While some of these responses can be simulated by wounding alone, we demonstrate that ECB larvae also secrete high levels of indole-3-acetic (IAA) into the surrounding feeding tunnel through contamination with their frass. Predictably, the application of auxin analogs exhibiting reduced catabolism promote maize stem protein accumulation above wounding alone. In addition to wound responses, ECB-derived IAA exists as a candidate herbivore effector promoting the increased nutritional content of maize stems.