Effects of caste on the constitutive and induced expression of genes associated with immunity and detoxification in Formosan subterranean termites

As social insects, Formosan subterranean termites (FSTs) live in dense populations in nest conditions that are conducive to microbial growth. Furthermore, termites are exposed to toxic substances in the soil and in their lignocellulose diet. Worker and soldier castes have different roles in the colony. Since workers forage and feed their nest mates via social interactions, we expect that they are more likely than soldiers to encounter pathogens and/or toxins. We tested the hypothesis that genes associated with immunity and/or detoxification have a higher constitutive expression level and/or are more readily inducible by bacteria and chemical challenges in workers than in soldiers. We tested putative genes from our Expressed Sequence Tag library for FSTs as reference genes (e.g. elongation factor-1-alpha and Cytoplasmic heat shock protein 70), immune response genes (e.g. antibacterial peptides and gram-negative binding proteins) and detoxification genes (e.g. cytochrome P450 and glutathione-S-transferase). Twenty FST workers and soldiers each from 3 colonies were challenged either by bacterial injection or by topical exposure to a sublethal concentration (0.5%) of Phenobarbital (PB). For each colony and each challenge, 5 challenged and 5 control workers and soldiers were randomly sampled in order to quantify constitutive and induced gene expression. Total RNA was extracted, normalized and synthesized into cDNA. Next, target genes were amplified via qRT-PCR. Differential expression was based on calculated baseline fluorescence using standard optimization methods (i.e. melt-curve analysis). Gene expression levels were compared between each sample group using mixed model analyses of variance (ANOVA). First results show higher constitutive expression of all of the immunity related genes in workers.