Abstract:

Antifreeze proteins (AFPs) are a family of proteins capable of protecting organisms from damage in freezing or sub-freezing conditions by controlling the growth of ice and inhibiting the recrystallization between ice granules, which are termed thermal hysteresis (TH) activity and recrystallization inhibition (RI) activity respectively. In comparison with the characteristic of high TH and low RI of fish AFPs and insect AFPs, antifreeze proteins of plants was low TH and high RI activity. In order to obtain antifreeze proteins with high TH and high RI activity, the complete cDNA of antifreeze protein genes (DcAFP and TmAFP) were cloned from Daucus carota and Tentbrio molitor. The two fusion antifreeze protein genes, Dc-TmAFP and Tm-DcAFP, were constructed series before and after by overlap extension PCR. The four genes were successfully transferred into Arabidopsis thaliana via Agrobacterium tumefaciens, and then the transgenic plants were cold treated. The frost-resistance of the transgenic plants was studied and analyzed. The results from statistical analysis of mortality and blade etiolation rate indicated that the AFPs had different functions which improved the cold resistance in many different ways. Hyperactive thermal hysteresis protein (THP) like TmAFP was a great help to depress the freezing point. However, when plant suffered from freeze injury a little longer, hyperactive ice re-crystallization inhibition protein (IRIP) like DcAFP kept stabilization of the fluid in the apoplast.