Introduction of a cold sensitivity-conferring mutation into the RTA-Bddsx hybrid system of Bactrocera dorsalis for establishment of a thermally controllable homozygous line.

Background: For efficient control of the economically important fruit pest Bactrocera dorsalis, a hybrid system combining ricin toxicity and sex-related alternative splicing of the doublesex gene has been developed. This system exhibits the expected female-specific lethal effect; however, the transgenic females do not survive, making it difficult to raise stable homozygous lines. Since modification of ricin toxin A chain (RTA) through a single-residue change (Gly > Arg ) leads to cold-sensitive posttranslational repression of its toxicity, we utilized this unique property to obtain RTA-Bddsx females that survive at low temperature for line maintenance.

Results: In transient expression experiments using embryonic injection, two groups treated with RTAcs-derived DNA (LERQcs and RTAcs) exhibited temperature-dependent effects. The toxicity was higher at 29 °C than at 18 °C. The proportion of males was close to 50% at 18 °C in all the tested groups except LERQcs-treated flies, which exhibited a high proportion of males (over 70%) at 29 °C. The results indicate the cold-sensitive responses of RTA and further suggest a female-specific lethal effect. Subsequently, 14 putative RTAcs-Bddsx transgenic Ds-Red G males were identified, and female-specific lethal effects were observed in Ds-Red G and G lines under cultivation at 29 °C but not at 18 °C. The male ratio can be increased to up to 95% in G line 001, indicating that RTAcs functions well in B. dorsalis.

Conclusion: The improved RTAcs-Bddsx system with conditional toxicity represents a novel and promising step toward the practical control of B. dorsalis. © 2021 Society of Chemical Industry.