Abstract
Formosan subterranean termites, Coptotermes formosanus Shiraki, live socially in microbial-rich habitats. To understand the molecular mechanism by which termites combat pathogenic microbes, a full-length normalized cDNA library and four Suppression Subtractive Hybridization (SSH) libraries were constructed from termite workers infected with entomopathogenic fungi (Metarhizium anisopliae and Beauveria bassiana), Gram-positive Bacillus thuringiensis and Gram-negative Escherichia coli, and the libraries were analyzed. From the high quality normalized cDNA library, 439 immune-related sequences were identified. These sequences were categorized as pattern recognition receptors (47 sequences), signal modulators (52 sequences), signal transducers (137 sequences), effectors (39 sequences) and others (164 sequences). From the SSH libraries, 27, 17, 22 and 15 immune-related genes were identified from each SSH library treated with M. anisopliae, B. bassiana, B. thuringiensis and E. coli, respectively. When the normalized cDNA library was compared with the SSH libraries, 37 immune-related clusters were found in common; 56 clusters were identified in the SSH libraries, and 259 were identified in the normalized cDNA library. The immune-related gene expression pattern was further investigated using quantitative real time PCR (qPCR). Important immune-related genes were characterized, and their potential functions were discussed based on the integrated analysis of the results. We suggest that normalized cDNA and SSH libraries enable us to discover functional genes transcriptome. The results remarkably expand our knowledge about immune-inducible genes in C. formosanus Shiraki and enable the future development of novel control strategies for the management of Formosan subterranean termites.
Highlights
The Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) is a serious pest that infests economically important crops and structures such as houses, buildings, boats, utility poles and underground telephone cables [1]
Our results suggested that exposure to entomopathogenic fungi (Metarhizium anisopliae strain 2049 and Beauveria bassiana strain 3005) and bacteria (Bacillus thuringiensis and Escherichia coli) greatly induce immune reactions that significantly increase the resistance in their homogenates to subsequent challenge
We identified one sequence encoding prophenoloxidase-activating factor in the normalized complementary DNA (cDNA) library. q-PCR results revealed that all of the microbes tested caused significant increases in proPOAF gene expression in C. formosanus Shiraki workers [1.24–3.46 -fold upon infection with fungi and 4.6–4.8 -fold upon infection with bacteria relative to control (Table 5)]
Summary
The Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) is a serious pest that infests economically important crops and structures such as houses, buildings, boats, utility poles and underground telephone cables [1]. This termite species has been estimated to cause damage valued at one billion dollars annually in the United States of America [2] and 0.8 billion RMB in the People’s Republic of China [3]. Five behavioral and biochemical adaptation mechanisms are involved in resistance to fungal infection: pathogen alarm behavior based on volatile organic compounds (VOCs) that warns foragers about the presence of lethal fungi and causes them to avoid infected areas; biochemical protection by the nestmates, who continuously secrete high amounts of toxic compounds, including naphthalene, n-hexanoic acid and nonanal, into the closed environment of the nest, walling-off infected areas of the colony, mutual grooming among nestmates, and removal of fungal-infected termites [1,5,6,7,8]
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