Isoprene deters insect herbivory by priming plant hormone responses

Isoprene, emitted by some plants, deters insect herbivory. However, the
associated biochemical and physiological responses that confer herbivory
resistance remain unknown. We used tobacco plants engineered to emit
isoprene (IE) and the non-emitting control (NE) to interpret
isoprene-mediated defense against herbivory in plants. Hornworm larvae
raised on IE plants exhibited stunted growth compared to those raised on
NE plants. Worms preferred to feed on NE rather than IE leaves, indicating
deterrent effects of isoprene on insect feeding. Worm feeding induced a
greater increase in jasmonic acid (JA), a crucial hormone for insect
resistance, in IE leaves compared to NE leaves. Assimilation rates were
stably maintained in IE plants suggesting a protective role of isoprene in
preserving photosynthetic efficiency during insect herbivory.
Wound-induced increase in isoprene emission correlated with the elevation
of key metabolites of the isoprene biosynthesis pathway. Our results
highlight JA-priming functions of isoprene and provide new insights into
isoprene-mediated defense against insect herbivory.