Expressing a modified cowpea trypsin inhibitor gene to increase insect tolerance against Pieris rapae in Chinese cabbage

To increase the tolerance of Chinese cabbage (Brassica campestris L. ssp. pekinensis) to Pieris rapae, we introduced a modified cowpea trypsin inhibitor (CpTI) gene, SCK, into various cultivars. SCK was derived from CpTI, an insect-resistance gene. The protein accumulating capacity of CpTI can be improved by adding a signal peptide sequence at the 5′ end and an endoplasmic reticulum-detained signal sequence at the 3′ end. Using an optimized Agrobacterium tumefaciens-mediated transformation system in Chinese cabbage, we obtained a maximum transformation efficiency of ~6.83%. Insect resistance tests and CpTI enzymatic assays showed that most of the transgenic plants had significant resistance to cabbage worm (Pieris rapae) larvae and that the plants with the highest levels of insect resistance had the greatest CpTI-related capacity, indicating a high correlation between SCK expression and insect resistance. An evaluation of segregation patterns in the independent transgenic line with the highest insect resistance, ‘ZB-08-04’, showed that kanamycin resistant versus sensitive plants segregated in a 3:1 Mendelian fashion. This study provides a potential germplasm resource for Chinese cabbage breeding in the future.