The cold resistant activities of multi-domain type III antifreeze proteins from Antarctic eelpout Lycodichths dearborni revealed by transgenic tobaccos

Abstract Type III antifreeze proteins (AFPIIIs) are small globular proteins that found in some polar fishes function to protect organisms from freezing damage. The transgenic expression of AFPs holds great promise for conferring cold tolerance to commercially important plant and animal species. We found from an Antarctic eelpout (Lycodichthys dearborni) multiple AFPIII genes that encode larger AFPIII isoforms containing up to 12 of the conventional AFPIII domains. Here we cloned AFPIII genes encode for monomer (LD1), dimer (LD2), trimer (LD3) and tetramer (LD4) AFPIII isoforms, and introduced them into tobacco plants. Pot-grown 4-week-old plants were then treated at 4 °C for 30 days, we found LD1, LD2, LD3 and LD4 plants showed relatively lower electrolyte leakage and lower content of malondialdehyde (MDA), but accumulated higher content of proline than control plants, indicating considerably improved membrane integrity under low temperature stress and better cold resistance. Comparing between the transgenic plants, the plants with the tetramer- and trimer-domain encoding AFPIII genes demonstrated higher cold-tolerant levels than those transformed by dimer- and monomer domain AFPIIIs. This study validated that fish AFPIIIs, especially the multidomain proteins may protect cells from non-freezing hypothermic stresses, apart from its well-known function as ice inhibition molecules at freezing temperature.