LAUSR

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 GABA to activate currents with high-micromolar or low-millimolar EC50 values, indicating the formation of functional homo-pentameric GABA receptors. Fipronil and picrotoxinin inhibited GABA-induced currents with high-nanomolar and low-micromolar 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. This article is protected by copyright. All rights reserved.