Three PilZ domain proteins, PlpA, PixA and PixB, have distinct functions in regulation of motility and development in Myxococcus xanthus

In bacteria, the nucleotide-based second messenger bis-(3’-5’)-cyclic dimeric GMP (c-di-GMP) binds to effectors to generate outputs in response to changes in the environment. In Myxococcus xanthus, c-di-GMP regulates type IV pili-dependent motility and the starvation-induced developmental program that results in formation of spore-filled fruiting bodies; however, little is known about the effectors that bind c-di-GMP. Here, we systematically inactivated all 24 genes encoding PilZ domain-containing proteins, which are among the most common c-di-GMP effectors. We confirm that the stand-alone PilZ-domain protein PlpA is important for regulation of motility independently of the Frz chemosensory system, and that Pkn1, which is composed of a Ser/Thr kinase domain and a PilZ domain, is specifically important for development. Moreover, we identify two PilZ-domain proteins that have distinct functions in regulating motility and development. PixB, which is composed of two PilZ domains and an acetyltransferase domain, binds c-di-GMP in vitro and regulates type IV pili-dependent and gliding motility in a Frz-dependent manner as well as development. The acetyltransferase domain is required and sufficient for function during growth while all three domains and c-di-GMP binding are essential for PixB function during development. PixA is a response regulator composed of a PilZ domain and a receiver domain, binds c-di-GMP in vitro, and regulates motility independently of the Frz system likely by setting up the polarity of the two motility systems. Our results support a model whereby PlpA, PixA and PixB act in independent pathways and have distinct functions in regulation of motility. Importance c-di-GMP signaling controls bacterial motility in many bacterial species by binding to downstream effector proteins. Here, we identify two PilZ domain-containing proteins in Myxococcus xanthus that bind c-di-GMP. We show that PixB, which contains two PilZ domains and an acetyltransferase domain, acts in a manner that depends on the Frz chemosensory system to regulate motility via the acetyltransferase domain while the intact protein and c-di-GMP binding are essential for PixB to support development. By contrast, PixA acts acts in Frz-independent mannerto regulate motility. Together with previous observations, we conclude that PilZ-domain proteins and c-di-GMP act in multiple independent pathways to regulate motility and development in M. xanthus.

Three PilZ domain proteins, PlpA, PixA and PixB, have distinct functions in regulation of motility and development in Myxococcus xanthus

In bacteria, the nucleotide-based second messenger bis-(3'-5')-cyclic dimeric GMP (c-di-GMP) binds to effectors to generate outputs in response to changes in the environment. In Myxococcus xanthus, c-di-GMP regulates type IV pili-dependent motility and the starvation-induced developmental program that results in the formation of spore-filled fruiting bodies; however, little is known about the effectors that bind c-di-GMP. Here, we systematically inactivated all 24 genes encoding PilZ domain-containing proteins, which are among the most common c-di-GMP receptors. We confirm that PlpA, a stand-alone PilZ-domain protein, is specifically important for motility and that Pkn1, which is composed of a Ser/Thr domain and a PilZ domain, is specifically important for development. Moreover, we identify two PilZ-domain proteins that have distinct functions in regulating motility and development. PixB, which is composed of two PilZ domains and an acetyltransferase domain, binds c-di-GMP in vitro and regulates type IV pili-dependent and gliding motility upstream of the Frz chemosensory system as well as development. The acetyltransferase domain is required and sufficient for function during growth while all three domains and c-di-GMP binding are essential for PixB function during development. PixA is a response regulator composed of a PilZ domain and a receiver domain, binds c-di-GMP in vitro, and regulates motility downstream of the Frz chemosensory system by setting up the polarity of the two motility systems. Our results support a model whereby the three proteins PlpA, PixA and PixB act in parallel pathways and have distinct functions to regulation of motility.

Chemosensory genes in the head of Spodoptera litura larvae

The tobacco cutworm Spodoptera litura (Lepidoptera: Noctuidae) is a polyphagous pest with a highly selective and sensitive chemosensory system involved in complex physiological behaviors such as searching for food sources, feeding, courtship, and oviposition. However, effective management strategies for controlling the insect pest populations under threshold levels are lacking. Therefore, there is an urgent need to formulate eco-friendly pest control strategies based on the disruption of the insect chemosensory system. In this study, we identified 158 putative chemosensory genes based on transcriptomic and genomic data for S. litura, including 45 odorant-binding proteins (OBPs, nine were new), 23 chemosensory proteins (CSPs), 60 odorant receptors (ORs, three were new), and 30 gustatory receptors (GRs, three were new), a number higher than those reported by previous transcriptome studies. Subsequently, we constructed phylogenetic trees based on these genes in moths and analyzed the dynamic expression of various genes in head capsules across larval instars using quantitative real-time polymerase chain reaction. Nine genes–SlitOBP8, SlitOBP9, SlitOBP25, SlitCSP1, SlitCSP7, SlitCSP18, SlitOR34, SlitGR240, and SlitGR242–were highly expressed in the heads of 3- to 5-day-old S. litura larvae. The genes differentially expressed in olfactory organs during larval development might play crucial roles in the chemosensory system of S. litura larvae. Our findings substantially expand the gene inventory for S. litura and present potential target genes for further studies on larval feeding in S. litura.

Seven Questions on the Chemical Ecology and Neurogenetics of Resource-Mediated Speciation

Adaptation to different environments can result in reproductive isolation between populations and the formation of new species. Food resources are among the most important environmental factors shaping local adaptation. The chemosensory system, the most ubiquitous sensory channel in the animal kingdom, not only detects food resources and their chemical composition, but also mediates sexual communication and reproductive isolation in many taxa. Chemosensory divergence may thus play a crucial role in resource-mediated adaptation and speciation. Understanding how the chemosensory system can facilitate resource-mediated ecological speciation requires integrating mechanistic studies of the chemosensory system with ecological studies, to link the genetics and physiology of chemosensory properties to divergent adaptation. In this review, we use examples of insect research to present seven key questions that can be used to understand how the chemosensory system can facilitate resource-mediated ecological speciation in consumer populations.

Coadaptation of the chemosensory system with voluntary exercise behavior in mice

Ethologically relevant chemical senses and behavioral habits are likely to coadapt in response to selection. As olfaction is involved in intrinsically motivated behaviors in mice, we hypothesized that selective breeding for a voluntary behavior would enable us to identify novel roles of the chemosensory system. Voluntary wheel running (VWR) is an intrinsically motivated and naturally rewarding behavior, and even wild mice run on a wheel placed in nature. We have established 4 independent, artificially evolved mouse lines by selectively breeding individuals showing high VWR activity (High Runners; HRs), together with 4 non-selected Control lines, over 88 generations. We found that several sensory receptors in specific receptor clusters were differentially expressed between the vomeronasal organ (VNO) of HRs and Controls. Moreover, one of those clusters contains multiple single-nucleotide polymorphism loci for which the allele frequencies were significantly divergent between the HR and Control lines, i.e., loci that were affected by the selective breeding protocol. These results indicate that the VNO has become genetically differentiated between HR and Control lines during the selective breeding process. Although the role of the vomeronasal chemosensory receptors in VWR activity remains to be determined, the current results suggest that these vomeronasal chemosensory receptors are important quantitative trait loci for voluntary exercise in mice. We propose that olfaction may play an important role in motivation for voluntary exercise in mammals.

Smelling in the dark: phylogenomic insights on the chemosensory system of a subterranean beetle

ABSTRACTThe chemosensory system has experienced relevant changes in subterranean animals, facilitating the orientation into darkness via the perception of specific chemical signals critical to survive in this particular environment. However, the genomic basis of chemoreception in cave-dwelling fauna is largely unexplored. We generated de novo transcriptomes for antennae and body samples of the troglobitic beetle Speonomus longicornis (whose characters suggest an extreme adaptation to the deep subterranean) in order to interrogate the evolutionary origin and diversification of the chemosensory gene repertoire across coleopterans through a phylogenomic approach. Our results suggested a diminished diversity of odorant and gustatory gene repertoires compared to polyphagous epigean beetles. Moreover, S. longicornis showed a large diversity of odorant-binding proteins, suggesting an important role of these proteins in capturing airborne chemical cues. We identified a gene duplication in the ionotropic co-receptor I R25a, a highly conserved single-copy gene in protostomes involved in thermal and humidity sensing. In addition, no homologous genes to sugar receptors or the ionotropic receptor IR41a were detected. Our findings suggest that the chemosensory gene repertoire of this cave beetle may have been reshaped by the low complexity of chemical signals of this particular environment, and that gene duplication and loss may have played an important role in the evolution of genes involved in chemoreception. Altogether, our results shed light on the genomic basis of chemoreception in a cave-dwelling invertebrate and pave the road towards understanding the genomic underpinnings of adaptation to the subterranean lifestyle at a deeper level.

Comparative genomic and transcriptomic analyses of chemosensory genes in the citrus fruit fly Bactrocera (Tetradacus) minax

The citrus fruit fly Bactrocera (Tetradacus) minax is a major and devastating agricultural pest in Asian subtropical countries. Previous studies have shown that B. minax interacts with plant hosts via the efficient chemosensory system. However, the molecular components of the B. minax chemosensory system have not been well characterized. Herein, we identified a total of 25 putative odorant-binding receptors (OBPs), 4 single-copy chemosensory proteins (CSPs) and 53 candidate odorant receptors (ORs) using a newly generated whole-genome dataset for B. minax. This study significantly extended the chemosensation-related gene profiles (particularly, OBPs and ORs) in six other tephritid species. Comparative transcriptome analysis of adult B. minax and Bactrocera dorsalis showed that there were 14 highly expressed OBPs (FPKM > 100) in B. dorsalis and 7 highly expressed ones in B. minax. The expression level of CSP3 gene and CSP4 gene was higher in B. dorsalis than that in B. minax. Comparative genomic and transcriptomic analyses of chemosensory genes in the citrus fruit fly B. minax provided new insights for preventive control of this agriculture important pest and closely related species.