Molecular cloning and pharmacology of Min‐UNC‐49B, a GABA receptor from the southern root‐knot nematode Meloidogyne incognita

Background Root‐knot nematodes are plant‐parasitic nematodes that cause immense damage to a broad range of cultivated crops by forming root galls, resulting in yield losses in crops. To facilitate the development of faster‐acting selective nematicides, we cloned three cDNAs encoding UNC‐49B proteins from the southern root‐knot nematode Meloidogyne incognita and examined their functional and pharmacological properties by two‐electrode voltage clamp electrophysiology using a Xenopus oocyte expression system. Results The three cloned cDNAs encoded Min‐UNC‐49B, Min‐UNC‐49B‐L and Min‐UNC‐49B‐XL; the last two proteins have longer N‑terminal regions than the first protein. When expressed in Xenopus oocytes, these proteins responded to γ‐aminobutyric acid (GABA) to activate currents with high‐micromolar or low‐millimolar half‐maximal effective concentration (EC50) values, indicating the formation of functional homo‐pentameric GABA receptors. Fipronil and picrotoxinin inhibited GABA‐induced currents with high‐nanomolar and low‐micromolar half‐maximal inhibitory concentration (IC50) values, respectively, in oocytes expressing Min‐UNC‐49B. The G2′A and T6′M mutations in the second transmembrane domain of Min‐UNC‐49B enhanced and reduced the sensitivity of Min‐UNC‐49B to these two antagonists, respectively. Samaderine B and SF‐14 inhibited GABA responses in oocytes expressing Min‐UNC‐49B with low‐micromolar and high‐nanomolar IC50 values, respectively. Ivermectin, α‐terpineol, thymol and methyl eugenol exerted dual effects on Min‐UNC‐49B by potentiating currents induced by low concentrations of GABA and inhibiting currents induced by high concentrations of GABA. Conclusion We have shown that structurally diverse compounds act at Min‐UNC‐49B GABA receptors. Our results may serve as a starting point to decipher the molecular function of native GABA receptors of plant‐parasitic nematodes, which could aid in the structure‐based design of novel nematicides. © 2020 Society of Chemical Industry Two‐electrode voltage clamp analysis shows that γ‐aminobutyric acid (GABA) activates Meloidogyne incognita UNC‐49B proteins to induce currents, and that structurally diverse natural and synthetic compounds potentiate or inhibit GABA responses.