Heterologous expression of Lolium perenne antifreeze protein confers chilling tolerance in tomato

Antifreeze proteins (AFP) are produced by certain plants, animals, fungi and bacteria that enable them to survive upon extremely low temperature. Perennial rye grass, Lolium perenne, was reported to possess AFP which protects them from cold environments. In the present investigation, we isolated AFP gene from L. perenne and expressed it in tomato plants to elucidate its role upon chilling stress. The T1 transgenic tomato lines were selected and subjected to molecular, biochemical and physiological analyses. Stable integration and transcription of LpAFP in transgenic tomato plants was confirmed by Southern blot hybridization and RT-PCR, respectively. Physiological analyses under chilling conditions showed that the chilling stress induced physiological damage in wild type (WT) plants, while the transgenic plants remained healthy. Total sugar content increased gradually in both WT and transgenic plants throughout the chilling treatment. Interestingly, transgenic plants exhibited remarkable alterations in terms of relative water content (RWC) and electrolyte leakage index (ELI) than those of WT. RWC increased significantly by 3-fold and the electrolyte leakage was reduced by 2.6-fold in transgenic plants comparing with WT. Overall, this report proved that LpAFP gene confers chilling tolerance in transgenic tomato plants and it could be a potential candidate to extrapolate the chilling tolerance on other chilling-sensitive food crops.