BMP signaling to pharyngeal muscle in the response to a bacterial pathogen regulates anti-microbial peptide expression and pharyngeal pumping.

Host response to pathogens recruits multiple tissues in part through conserved cell signaling pathways. In , the bone morphogenetic protein (BMP) like DBL-1 signaling pathway has a role in the response to infection in addition to other roles in development and postdevelopmental functions. In the regulation of body size, the DBL-1 pathway acts through cell autonomous signal activation in the epidermis (hypodermis). We have now elucidated the tissues that respond to DBL-1 signaling upon exposure to two bacterial pathogens. The receptors and Smad signal transducers for DBL-1 are expressed in pharyngeal muscle, intestine, and epidermis. We demonstrate that expression of receptor-regulated Smad (R-Smad) gene in the pharynx is sufficient to improve the impaired survival phenotype of mutants and that expression of in the intestine has no effect when exposing worms to bacterial infection of the intestine. We also show that two antimicrobial peptide genes - and - are regulated by DBL-1 signaling through R-Smad SMA-3 activity in the pharynx. Finally, we show that pharyngeal pumping activity is reduced in mutants and that other pharynx-defective mutants also have reduced survival on a bacterial pathogen. Our results identify the pharynx as a tissue that responds to BMP signaling to coordinate a systemic response to bacterial pathogens.