Genetic dissection of anopheles gambiae Gut epithelial responses to serratia marcescens

Genetic variation in the mosquito Anopheles gambiae profoundly influences its ability to transmit malaria. Mosquito gut bacteria are shown to influence the outcome of infections with Plasmodium parasites and are also thought to exert a strong drive on genetic variation through natural selection; however, a link between antibacterial effects and genetic variation is yet to emerge. Here, we combined SNP genotyping and expression profiling with phenotypic analyses of candidate genes by RNAi-mediated silencing and 454 pyrosequencing to investigate this intricate biological system. We identified 138 An. gambiae genes to be genetically associated with the outcome of Serratia marcescens infection, including the peptidoglycan recognition receptor PGRPLC that triggers activation of the antibacterial IMD/REL2 pathway and the epidermal growth factor receptor EGFR. Silencing of three genes encoding type III fibronectin domain proteins (FN3Ds) increased the Serratia load and altered the gut microbiota composition in favor of Enterobacteriaceae. These data suggest that natural genetic variation in immune-related genes can shape the bacterial population structure of the mosquito gut with high specificity. Importantly, FN3D2 encodes a homolog of the hypervariable pattern recognition receptor Dscam, suggesting that pathogen-specific recognition may involve a broader family of immune factors. Additionally, we showed that silencing the gene encoding the gustatory receptor Gr9 that is also associated with the Serratia infection phenotype drastically increased Serratia levels. The Gr9 antibacterial activity appears to be related to mosquito feeding behavior and to mostly rely on changes of neuropeptide F expression, together suggesting a behavioral immune response following Serratia infection. Our findings reveal that the mosquito response to oral Serratia infection comprises both an epithelial and a behavioral immune component

Short-range control of cell differentiation in the Arabidopsis root meristem

Meristems are distinctive regions of plants that have capacity for continuous growth. Their developmental activity generates the majority of plant organs. It is currently unknown how cell division and cell differentiation are orchestrated in meristems, although genetic studies have demonstrated the relevance of a proper balance between the two processes. Root meristems contain a distinct central region of mitotically inactive cells, the quiescent centre, the function of which has remained elusive until now. Here we present laser ablation and genetic data that show that in Arabidopsis thaliana the quiescent centre inhibits differentiation of surrounding cells. Differentiation regulation occurs within the range of a single cell, in a manner strikingly similar to examples in animal development, such as during delamination of Drosophila neuroblasts. Our data indicate that pattern formation in the root meristem is controlled by a balance between shortrange signals inhibiting differentiation and signals that reinforce cell fate decisions