Premium
Functional characterization of Bacillus thuringiensis Cry toxin receptors explains resistance in insects
Author(s) -
Tanaka Shiho,
Endo Haruka,
Adegawa Satomi,
Kikuta Shingo,
Sato Ryoichi
Publication year - 2016
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.13952
Subject(s) - bacillus thuringiensis , toxin , receptor , xenopus , microbiology and biotechnology , sf9 , biology , bombyx mori , biophysics , chemistry , biochemistry , spodoptera , gene , bacteria , recombinant dna , genetics
Bacillus thuringiensis produces Cry toxins, which are used as insecticides in sprays and in transgenic crops. However, little is known about the function of Cry toxin receptors and the mechanisms that determine their binding specificity and activity. In this study, the cRNA s of Bombyx mori ABC transporter C2 (Bm ABCC 2), the toxin‐binding region of cadherin‐like receptor (BtR175‐ TBR ), or aminopeptidase N1 (Bm APN 1) were injected into Xenopus oocytes, and the Cry1Aa‐dependent cation‐selective pore formation activities of these receptors were analyzed using a two‐electrode voltage clamp. Cation current passing through the pores was detected within 25 s, and increased in a linear fashion in Bm ABCC 2‐expressing oocytes treated with 88 n m Cry1Aa. This result suggested that Cry1Aa continuously made stable pores with the help of Bm ABCC 2. In contrast, no cation current was observed until 60 min after incubation with 500 n m Cry1Aa in BtR175 TBR ‐expressing oocytes even though oligomerization of Cry1Aa progressed. This result indicated that in the presence of BtR175‐ TBR most of the oligomerized toxin could not enter the cell membrane. However, oocytes that simultaneously expressed both receptors demonstrated that BtR175‐ TBR exerted a synergistic effect with Bm ABCC 2 on pore formation in the presence of 22 n m Cry1Aa. These results confirm that the main reason for moderate‐level resistance in insects lacking the cadherin‐like receptor but expressing ABCC 2 is the absence of a similar synergistic promotion of toxin oligomerization. Similar to results from our previous report evaluating ectopic expression in the Sf9/Baculovirus system, Bm APN 1 could not by itself cause Cry1A‐related pore formation, despite the fact that Bm APN 1 gathered toxin on the oocytes as well as Bm ABCC 2 did.