Host plant driven plasticity in the salivary glands of Trichoplusia ni

Generalist herbivores feed on a wide array of plants and need to adapt to varying host qualities and defenses. One of the first insect derived secretions to come in contact with the plant is the saliva. Insect saliva is involved in both the pre-digestion of the host plant as well as induction/suppression of plant defenses, yet how the salivary glands respond to changes in host plant at the transcriptional and translational levels is largely unknown. The objective of this study was to determine how saliva composition varies according to the host plant on which the insect is feeding. In order to determine this, cabbage looper (Trichoplusia ni) larvae were reared on cabbage (high quality host), tomato (low quality host), and pinto bean artificial diet. Salivary glands were dissected from fifth instar larvae and used to extract RNA for RNASeq (gene expression differences) and proteins for iTRAQ analysis (protein differences). This study established a transcriptome and proteome library for T. ni salivary glands of 14037 transcripts and 441 proteins, respectively. There was massive remodeling of the glands including 4501 genes differentially expressed (using artificial diet as a calibrator) as well as 79 proteins. Gene expression was most similar between cabbage and artificial diet, diets on which larvae perform best. The differentially expressed genes and proteins include several putatively involved in detoxification as well as post-translational mechanisms. These results confirm the hypothesis that salivary glands of T. ni go through a massive remodeling both at the gene and protein level based on their diet.