Molecular cloning and pharmacology of Min-UNC-49B, aGABAreceptor 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 nematodeMeloidogyne incognitaand examined their functional and pharmacological properties by two-electrode voltage clamp electrophysiology using aXenopusoocyte 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 inXenopusoocytes, these proteins responded to gamma-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, alpha-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. (c) 2020 Society of Chemical Industry

Automated summary

Three cDNAs encoding UNC-49B proteins were cloned from Meloidogyne incognita, which responded to GABA and various antagonists in Xenopus oocytes. The research provides insights for the design of novel nematicides targeting plant-parasitic nematodes.