Drosophilalarval gut transcriptome reveals a microbe-mediated intestinal tissue growthviaEcdysone during adaptive growth

Juvenile growth is an adaptive trait since chronic undernutrition leads to reduced growth rate and delayed maturation. UsingDrosophilaand mouse gnotobiotic models, we previously established the evolutionarily conserved influence of the intestinal microbiota and selectedLactobacillistrains on juvenile growth. Here we aimed to identify the molecular mechanisms underlying microbe-mediatedDrosophilaadaptive growth. Since the intestine is the interface of host-microbe interactions, we conducted an analysis of the larval midgut transcriptome in presence or absence of an intestinalLactobacillistrain representative of theDrosophilamicrobiota. Among the different biological processes identified, Ecdysone signaling has emerged as a newLactobacilli-mediated signature. Through functional and morphometrical approaches, we show that, upon bacteria association, intestinal Ecdysone is not rate limiting for the larval systemic plastic growth but required for the adaptation of midgut growth toLactobacilli. Our results reveal a tissue-specific contribution of the pleiotropic hormone Ecdysone in the control of midgut adaptive growth and maturation.