Identification of a vital transcription factor of the alanine aminotransferase in the brown planthopper and its upstream regulatory pathways.

The brown planthopper (Nilaparvata lugens) is an important insect pest of rice, and can rapidly adapt to insect-resistant rice varieties. In our previous studies, alanine aminotransferase in N. lugens (NlALT) was found to play an important role in the adaptation of the brown planthopper to resistant rice IR36. Here, we further identified CCAAT/enhancer binding protein (NlC/EBP) as a vital transcription factor of NlALT. Nlp38b in the MAPKs pathway regulated the expression of NlALT by influencing the phosphorylation level of NlC/EBP. In addition, we found that NlGRL101, a G protein-coupled receptor (GPCR), was significantly higher expressed in the N. lugens population adapted to IR36 (P-IR36). After knockdown of NlGRL101 through RNAi in P-IR36 population, lower expressions of Nlp38b and NlC/EBP, along with reduced phosphorylation levels of Nlp38b and NlC/EBP were observed; moreover, NlALT activity and honeydew amount were decreased by 15.68% and 76.08%, respectively. These results indicated that insect-resistant rice IR36 induced expression of NlGRL101, which enhanced expression of NlALT through Nlp38b and NlC/EBP. These findings are helpful for better understanding of insect adaptation to resistant crop varieties.