A Genome-Wide Survey for Host Response of Silkworm, Bombyx mori during Pathogen Bacillus bombyseptieus Infection Lulin Huang1,3, Tingcai Cheng 2 , Pingzhen Xu 1 , Daojun Cheng 1 , Ting Fang 1 , Qingyou Xia1,2* 1 Institute of Sericulture and Systems Biology, Southwest University, Chongqing, China, 2 Institute of Agronomy and Life Science, Chongqing University, Chongqing, China, 3 Institute of Economic Crops Breeding and Cultivation, Sichuan Academy of Agricultural Sciences, Chengdu, China Abstract Host-pathogen interactions are complex relationships, and a central challenge is to reveal the interactions between pathogens and their hosts. Bacillus bombysepticus (Bb) which can produces spores and parasporal crystals was firstly separated from the corpses of the infected silkworms (Bombyx mori). Bb naturally infects the silkworm can cause an acute fuliginosa septicaemia and kill the silkworm larvae generally within one day in the hot and humid season. Bb pathogen of the silkworm can be used for investigating the host responses after the infection. Gene expression profiling during four time-points of silkworm whole larvae after Bb infection was performed to gain insight into the mechanism of Bb-associated host whole body effect. Genome-wide survey of the host genes demonstrated many genes and pathways modulated after the infection. GO analysis of the induced genes indicated that their functions could be divided into 14 categories. KEGG pathway analysis identified that six types of basal metabolic pathway were regulated, including genetic information processing and transcription, carbohydrate metabolism, amino acid and nitrogen metabolism, nucleotide metabolism, metabolism of cofactors and vitamins, and xenobiotic biodegradation and metabolism. Similar to Bacillus thuringiensis (Bt), Bb can also induce a silkworm poisoning-related response. In this process, genes encoding midgut peritrophic membrane proteins, aminopeptidase N receptors and sodium/calcium exchange protein showed modulation. For the first time, we found that Bb induced a lot of genes involved in juvenile hormone synthesis and metabolism pathway upregulated. Bb also triggered the host immune responses, including cellular immune response and serine protease cascade melanization response. Real time PCR analysis showed that Bb can induce the silkworm systemic immune response, mainly by the Toll pathway. Anti-microorganism peptides (AMPs), including of Attacin, Lebocin, Enbocin, Gloverin and Moricin families, were upregulated at 24 hours post the infection. Citation: Huang L, Cheng T, Xu P, Cheng D, Fang T, et al. (2009) A Genome-Wide Survey for Host Response of Silkworm, Bombyx mori during Pathogen Bacillus bombyseptieus Infection. PLoS ONE 4(12): e8098. doi:10.1371/journal.pone.0008098 Editor: Georg Ha¨cker, Technical University Munich, Germany Received July 8, 2009; Accepted November 4, 2009; Published December 1, 2009 Copyright: 2009 Huang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by research grants from the National Basic Research Program of China (http://www.973.gov.cn/English/Index.aspx), grant number No. 2005CBI21000, to QYX; the Ministry of Education Development Plan of Changjiang Scholars and their Innovative Team, grant number IRT0750, to QYX. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: xiaqy@swu.edu.cn Introduction A lot species of bacteria belonging to the genus Bacillus have established a systemic infection in a variety of hosts including humans, animals and insects [1–3]. Some species of Bacillus are investigated more than others for their closer connection with human beings. For example, Bacillus thuringiensis, as a good model, was well studied on its insecticidal mechanism by producing crystal proteins and has been developed as commercial biological products to control insect pests [4–6]. Bacillus cereus can produce food poisoning toxins generally causes summer food poisoning [7,8]. Studies revealed that fur gene of Bacillus cereus regulates iron metabolism and is required for full virulence [9]. Bacillus anthracis infection results in the anthrax disease of human and animals [10,11]. In the process of infection host macrophages, B. anthracis can rapidly adapt to the intracellular environment, and modulate its metabolic pathways such as energy metabolism and biosynthe- sis of cofactors for its intracellular growth [12]. For other pathogens, systematic gene expression such as basal metabolic pathways also can be modulated during its infection. For example, during the developmental cycle and iron depletion-mediated persistence of Chlamydophila pneumoniae, its transcriptome changes in many functional groups such as the cell envelope and the translation machinery [13]. On the host side, hosts’ behaviours can be significantly dominated by pathogens infection. B. anthracis ames spores also significantly affect the expression of approximately 580 host genes in murine lung, spleen, and heart tissues at 8- and 48-h time points [14]. Recently, the genome-wide analysis of the interaction between the endosymbiotic bacterium Wolbachia and its Drosophila host also showed involvement of antimicrobial humoral response and negative regulation of cell proliferation of its host [15]. Studies on transcriptional response of Choristoneura fumiferana to Cry1Ab protoxin from B. thuringiensis showed a number of metabolic and stress-related genes that were either transcriptionally enhanced or repressed after protoxin exposure, including DNA polymerase processivity factor1, fatty acid binding, cytoskeletal constituent, serine proteinase inhibitor, serpin, translation initiation factor and so on [16]. PLoS ONE | www.plosone.org 1 December 2009 | Volume 4 | Issue 12 | e8098