Drooling Over Insect-Induced Galls: Salivary Origins of Exogenous Cytokinins by Stephannie Seng

Stephannie Seng

SFSU

In an effort to understand how insects induce plant tumors, we are examining the expression levels of genes in the tRNA-ipt cytokinin biosynthesis pathway in various tissues of Eurosta solidaginis, a tumor inducing insect.

ABSTRACT

Cytokinins are a class of plant growth hormones which play an important role in a variety of plant processes. Exogenous cytokinins found in plant‐manipulating insects are known to contribute to many effects on host plants. One of the most apparent effects is that cytokinins, in the presence of auxin, lead to cell division and the proliferation of plant tissue forms plant galls, tumor-like structures. Cytokinins also lead to the formation of mobilizing sinks resulting in the reallocation of sugars and nutrients to the gall site, where these nutrients sustain gall and insect growth. We are examining the expression levels of genes in the tRNA-ipt cytokinin biosynthesis pathway in various tissues of Eurosta solidaginis, a tumor inducing insect. Up‐regulation of these genes in the salivary gland implies that cytokinins are being synthesized in the salivary glands by either the insect and/or its bacterial symbiont, and secreted into the host plant. Along with the widespread distribution of cytokinins in insects, their production and secretion from the salivary glands would further imply that cytokinins are amplified and used by insects to manipulate their host plants. In addition, cytokinins and the genes involved in their synthesis are widespread among plant-eating insect groups, so phytohormone mediated plant manipulation may not be exclusive to gall‐inducing insects, rather it may also be widespread among plant‐eating insects.

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