Decision making in C. elegans chemotaxis to alkaline pH: Competition between two sensory neurons, ASEL and ASH

Low-acidity acid rain promoted the morphological development of tomato roots and reduced the infection of root-knot nematodes

Acid rain remains a critical environmental concern that indirectly impacts plant root systems through soil acidification. However, its effects on physiological and biochemical responses in plants, as well as interactions with root-knot nematode (RKN, Meloidogyne javanica) infection, remain insufficiently characterized. This study investigated the tolerance mechanisms of tomato roots to RKNs and simulated acid rain (SAR) through a factorial experiment combining four SAR treatments (pH 3.5, 4.5, 5.5, and control CK) with nematode inoculation (NI: non-inoculated; MI: inoculated), key parameters including chlorophyll fluorescence dynamics, antioxidant enzyme activity, root morphology traits, and nematode infection indices were systematically analyzed. Our results indicate that SAR significantly reduced the incidence index of soil RKNs. Conversely, SAR treatments with pH4.5 and 5.5 enhanced root length by 27 % and 30 %, respectively. SAR at pH 4.5 increased root surface area by 40 % and root volume by 54 %. The effects of SAR at pH 5.5 on soil nutrients and chlorophyll fluorescence were not significant. However, SAR at pH 3.5 and 4.5 significantly reduced the Fv/Fm and Y(II), as well as NH4+-N and available K content. High-intensity SAR also intensified the inhibitory effect of RKNs on photosynthetic parameters, such as Y(II) and qP. Furthermore, SAR enhanced SOD activity and increased MDA content in conditions without nematode infection. Under SAR at pH 4.5 and 5.5, ABA and JA contents decreased, with further analysis revealing a significant correlation between the reduction in ABA and JA and the increase in root length. Overall, our study demonstrates that acid rain of pH 4.5 can, to some extent, reduce root-knot nematode infection and promote the development of root morphology, while acid rain at pH 3.5 causes significant harm to plants. This research provides an important reference for further exploration of the long-term effects of acid rain on plant growth and soil ecosystem in the future.

The G-Protein-Coupled Receptor SRX-97 Is Required for Concentration-Dependent Sensing of Benzaldehyde in Caenorhabditis elegans

The G-protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors (GPCRs) in the olfactory system function to sense the surrounding environment and respond to various odorants. The genes coding for olfactory receptors in Caenorhabditis elegans are larger in number in comparison to those in mammals, suggesting complexity in the receptor-odorant relationships. Recent studies have shown that the same odorant in different concentrations could act on multiple receptors in different neurons to induce attractive or repulsive responses. The ASH neurons are known to be responsible for responding to high concentrations of volatile odorants. Here, we characterize a new GPCR, SRX-97. We found that the srx-97 promoter drives expression specifically in the head ASH and tail PHB chemosensory neurons of C. elegans. Moreover, the SRX-97 protein localizes to the ciliary ends of the ASH neurons. Analysis of clustered regularly interspaced short palindromic repeats (CRISPR)-based deletion mutants of the srx-97 locus suggests that this gene is involved in recognition of high concentrations of benzaldehyde. This was further confirmed through rescue and neuronal ablation experiments. Our work brings novel insights into concentration-dependent receptor function in the olfactory system, and provides details of an additional molecule that helps the animal navigate its surroundings.

Alkaline pH sensor molecules

Animals can survive only within a narrow pH range. This requires continual monitoring of environmental and body-fluid pH. Although a variety of acidic pH sensor molecules have been reported, alkaline pH sensor function is not well understood. This Review describes neuronal alkaline pH sensors, grouped according to whether they monitor extracellular or intracellular alkaline pH. Extracellular sensors include the receptor-type guanylyl cyclase, the insulin receptor-related receptor, ligand-gated Cl- channels, connexin hemichannels, two-pore-domain K+ channels, and transient receptor potential (TRP) channels. Intracellular sensors include TRP channels and gap junction channels. Identification of molecular mechanisms underlying alkaline pH sensing is crucial for understanding how animals respond to environmental alkaline pH and how body-fluid pH is maintained within a narrow range.