SpCYS, a cystatin gene from wild potato (Solanum pinnatisectum), is involved in the resistance against Spodoptera litura

Cysteine proteinase inhibitor (cystatin) genes belong to one family of proteinase inhibitors and play an important role in the resistance to insect pests. Cystatin (CYS) genes have been studied in different plant–insect interactions, but there are few reports about the importance of potato cystatin genes. In this study, a cystatin gene named SpCYS was characterized from the wild diploid potato Solanum pinnatisectum Dun, which exhibits high resistance to insect pests. We also investigated the impact of SpCYS in the development of Spodoptera litura when feed from leaves of genetically modified potato. Bioinformatic analysis revealed that SpCYS encoded protein possessed conserved domains of the cystatin family. The SpCYS expression was observed in leaves, stems, roots and tubers with the expression level being almost the same in roots, stems and leaves but greater in tubers. After mechanical damage, SpCYS expression in leaves was induced reaching its peak at 9 h and then decreased to normal levels. Further, we constructed transgenic lines of cultivated potato (cultivar Desiree) expressing SpCYS and performed insect bioassays and feeding preference experiments. Both tests showed that the over-expression of SpCYS lowered the weight increase rate of both Spodoptera litura larvae and pupa. S. litura larvae preferred to feed on the leaves of non-transformed controls rather than the transgenic lines. Taken together, our data suggest that SpCYS is a significant asset for the defense mechanism of potato against S. litura.