Cytokinin transfer by a free-living mirid to <i>Nicotiana attenuata</i> recapitulates a strategy of endophytic insects.

Abstract

Endophytic insects provide the textbook examples of herbivores that manipulate their host plant's physiology, putatively altering source/sink relationships by transferring cytokinins (CK) to create 'green islands' that increase the nutritional value of infested tissues. However, unambiguous demonstrations of CK transfer are lacking. Here we show that feeding by the free-living herbivore <i>Tupiocoris notatus</i> on <i>Nicotiana attenuata</i> is characterized by stable nutrient levels, increased CK levels and alterations in CK-related transcript levels in attacked leaves, in striking similarity to endophytic insects. Using ¹⁵N-isotope labeling, we demonstrate that the CK <i>N</i>⁶-isopentenyladenine (IP) is transferred from insects to plants via their oral secretions. In the field, <i>T. notatus</i> preferentially attacks leaves with transgenically increased CK levels; plants with abrogated CK-perception are less tolerant of <i>T. notatus</i> feeding damage. We infer that this free-living insect uses CKs to manipulate source/sink relationships to increase food quality and minimize the fitness consequences of its feeding.