32The G-protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors in 33 the olfactory system function to sense the surroundings and respond to various 34 odorants. The genes encoding for the olfactory receptors in C. elegans are larger in 35 number in comparison to those in mammals, suggesting complexity in the receptor-36 odorant relationships. Recent studies have shown that the same odorant in different 37 concentration could act on multiple receptors in different neurons to induce attractive or 38 repulsive responses. The ASH neuron is known to be responsible for responding to high 39 concentrations of volatile odorants. Here we characterize a new GPCR, SRX-97. We 40 found that the srx-97 promoter shows expression specifically in the head ASH and tail 41 PHB chemosensory neurons of C. elegans. Further, the SRX-97 protein localizes to the 42 ciliary ends of the ASH neurons. Analysis of CRISPR/based deletion mutants of the srx-43 97 gene suggest that this gene is involved in the recognition of high concentrations of 44 benzaldehyde. This was further confirmed through rescue and neuronal ablation 45 experiments. Our work gives insight into concentration dependent receptor function in 46 the olfactory system and provides details of an additional molecule that could help the 47 animal navigate its surroundings. 48 49 50 51 52 53 54Animals sense a wide range of volatile and water-soluble chemicals through their 55 olfactory system. The olfactory system is made up of several neurons that express 56 different sets of seven-transmembrane G-protein coupled receptors (GPCRs). The 57 odorant binds to the GPCRs, activating distinct intracellular signaling pathways and thus 58 directing the animal's response to different external cues (reviewed in (Erlandson et al., 59 2018; Katritch et al., 2013)). 60C. elegans is a soil-dwelling animal that possesses a well-developed chemosensory 61 system for their survival. They perceive their environment through various sensory 62 neurons to find food sources, mates and to escape from dangerous conditions. In C. 63 elegans 13 pairs of chemosensory neurons carry out majority of chemosensation, they 64 express around 1300 functional chemosensory (cs) G-protein coupled receptors 65 (GPCR) (Robertson and Thomas, 2006; Vidal et al., 2018). This diversity of csGPCRs 66 allows the animal to discriminate between different odors. Thus, the specific expression 67 of any GPCR or combined expression of different GPCRs on a specific neuron or 68 different neurons can modulate the animal's perception towards the same odorant. 69The olfactory neurons that are involved in sensing a large number of attractive cues are 70 AWA and AWC. These two pairs of neurons are involved in showing chemotaxis to 71 various chemicals like diacetyl, isoamyl alcohol, pyrazine, benzaldehyde, and butanone 72 (Bargmann et al., 1993; Colbert et al., 1997; Troemel et al., 1995). The avoidance 73 behavior towards the repellents nonanone and 1-octanol is mediated through the 74 sensory neurons AWB...

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