Caterpillar Labial Saliva Alters Tomato Plant Gene Expression Richard O. Musser & Sue M. Hum-Musser & Henry K. Lee & Brittany L. DesRochers & Spencer A. Williams & Heiko Vogel Received: 15 June 2012 / Revised: 7 September 2012 / Accepted: 25 September 2012 # Springer Science+Business Media New York 2012 Abstract We examined the effects of Helicoverpa zea cater- pillar labial saliva on tomato plant gene expression. Caterpil- lars with labial salivary glands (mock-ablated) and without (ablated) were fed on tomato plants for 24 hr; then, the leaf mRNAwas analyzed with tomato microarrays. Analysis of the transcript profiles revealed 384 expressed sequence tags (ESTs) that were significantly altered due to herbivory com- pared to the non-wounded plants. The majority of the ESTs were quantitatively altered more so by mock-ablated caterpil- lars with labial salivary glands than ablated caterpillars. Par- ticularly notable, ESTs encoding acid phosphatase, arginase, acidic endochitinase, dehydrin, polyphenol oxidase, protease inhibitors, and threonine deaminase were more highly stimu- lated by mock-ablated caterpillars than ablated caterpillars. In addition, tomato leaves were mechanically wounded with scissors and painted with labial salivary gland extract, auto- claved salivary gland extract, or water, and compared to non- wounded tomato plants. After 4 hr, these leaves were collected and a tomato microarray analysis of the mRNA revealed correlation of the gene expression of these leaves altered by mechanical wounding and painted with salivary gland extract to the gene expression of leaves fed on by mock-ablated caterpillars. We show that caterpillar labial saliva is an important component of herbivory that can alter plant gene expression. Keywords Caterpillar saliva . Herbivory . Gene expression . Glucose oxidase . Plant defense Introduction Increasing evidence suggests that plants, to some degree, can differentiate between tissue damage caused by environmental factors (wind, hail) and actual insect herbivory that would result in a more continuous loss of tissues (Howe and Jander, 2008). The herbivore’ s unique style and tempo of wounding also can function as a reliable signal of herbivory. Mithöfer et al. (2005) utilized a computer-controlled tool, “MecWorm,” that realistically mimicked caterpillar wounding and stimulat- ed Lima bean plant volatiles similar to the actual caterpillar. However, further MecWorm experiments revealed that vola- tile expression is altered by additional herbivory factors, such as insect oral secretions, beyond physical plant tissue damage (Maffei et al., 2007a,b). Insect oral secretions contain many different factors that potentially affect a wide range of plant physiology, and can function as elicitors that stimulate the plant’ s anti-herbivore defenses (Mattiacci et al., 1995; Alborn et al., 1997, 2000; Reymond et al., 2000, 2004; Hermsmeier et al., 2001; Schittko et al., 2001; Lou and Baldwin, 2003; De Vos et al., 2005, 2006; Ralph et al., 2006a,b; Schmelz et al., 2006, 2009; Lawrence et al., 2008). Herbivore elicitors can include many compounds such as enzymes (β-glycosidase, glucose oxidase (GOX), ribonuclease), small peptides called inceptins, fatty acid- amino acid conjugates such as volicitin, and sulfated α-hy- droxy fatty acids called caeliferins (Musser et al., 2002a, b, 2005a, b; Howe and Jander, 2008; Mithöfer and Boland, 2008). Musser et al. (2002a, 2005a, b, 2006) first characterized Electronic supplementary material The online version of this article (doi:10.1007/s10886-012-0198-3) contains supplementary material, which is available to authorized users. R. O. Musser (*) : S. M. Hum-Musser : H. K. Lee : B. L. DesRochers : S. A. Williams Department of Biological Sciences, Western Illinois University, Macomb, IL 61455, USA e-mail: RO-Musser@wiu.edu H. Vogel Department of Entomology, Max Planck Institute for Chemical Ecology, Beutenberg Campus, Jena 07745, Germany J Chem Ecol DOI 10.1007/s10886-012-0198-3