Heparan sulfate proteoglycan molecules, syndecan and perlecan, have distinct roles in the maintenance of Drosophila germline stem cells.

The Drosophila female germline stem cell (GSC) niche provides an excellent model for understanding the stem cell niche in vivo. The GSC niche is composed of stromal cells that provide growth factors for the maintenance of GSCs and the associated extracellular matrix (ECM). Although the function of stromal cells/growth factors has been well studied, the function of the ECM in the GSC niche is largely unknown. In this study, we investigated the function of syndecan and perlecan, molecules of the heparan sulfate proteoglycan (HSPG) family, as the main constituents of the ECM. We found that both of these genes were expressed in niche stromal cells, and knockdown of them in stromal cells decreased GSC number, indicating that these genes are important niche components. Interestingly, our genetic analysis revealed that the effects of syndecan and perlecan on the maintenance of GSC were distinct. While the knockdown of perlecan in the GSC niche increased the number of cystoblasts, a phenotype suggestive of delayed differentiation of GSCs, the same was not true in the context of syndecan. Notably, the overexpression of syndecan and perlecan did not cause an expansion of the GSC niche, opposing the results reported in the context of glypican, another HSPG gene. Altogether, our data suggest that HSPG genes contribute to the maintenance of GSCs through multiple mechanisms, such as the control of signal transduction, and ligand distribution/stabilization. Therefore, our study paves the way for a deeper understanding of the ECM functions in the stem cell niche.

Tobacco Root Endophytic Arthrobacter Harbors Genomic Features Enabling the Catabolism of Host-Specific Plant Specialized Metabolites.

Plant roots constitute the primary interface between plants and soilborne microorganisms and harbor microbial communities called the root microbiota. Recent studies have demonstrated a significant contribution of plant specialized metabolites (PSMs) to the assembly of root microbiota. However, the mechanistic and evolutionary details underlying the PSM-mediated microbiota assembly and its contribution to host specificity remain elusive. Here, we show that the bacterial genus Arthrobacter is predominant specifically in the tobacco endosphere and that its enrichment in the tobacco endosphere is partially mediated by a combination of two unrelated classes of tobacco-specific PSMs, santhopine and nicotine. We isolated and sequenced Arthrobacter strains from tobacco roots as well as soils treated with these PSMs and identified genomic features, including but not limited to genes for santhopine and nicotine catabolism, that are associated with the ability to colonize tobacco roots. Phylogenomic and comparative analyses suggest that these genes were gained in multiple independent acquisition events, each of which was possibly triggered by adaptation to particular soil environments. Taken together, our findings illustrate a cooperative role of a combination of PSMs in mediating plant species-specific root bacterial microbiota assembly and suggest that the observed interaction between tobacco and Arthrobacter may be a consequence of an ecological fitting process. IMPORTANCE Host secondary metabolites have a crucial effect on the taxonomic composition of its associated microbiota. It is estimated that a single plant species produces hundreds of secondary metabolites; however, whether different classes of metabolites have distinctive or common roles in the microbiota assembly remains unclear. Here, we show that two unrelated classes of secondary metabolites in tobacco play a cooperative role in the formation of tobacco-specific compositions of the root bacterial microbiota, which has been established as a consequence of independent evolutionary events in plants and bacteria triggered by different ecological effects. Our findings illustrate mechanistic and evolutionary aspects of the microbiota assembly that are mediated by an arsenal of plant secondary metabolites.