The use of antifreeze proteins for frost protection in sensitive crop plants

Antifreeze proteins (AFPs), also known as ice binding proteins (IBPs), have evolved as an important adaptation in numerous organisms exposed to subzero temperatures. Plant AFPs have only been identified in freeze tolerant species (those able to survive extracellular freezing). Consequently, plant AFPs have very low specific activities as they have not evolved to completely prevent ice formation in the plant. In contrast, fish and most insect AFPs function to prevent freezing in species that have evolved freeze avoidance mechanisms. Therefore, the activity of these AFPs, especially those of insects (as they are generally exposed to considerably lower temperatures than fish), is much greater. The ability of AFPs to non-colligatively lower the freezing point of water (thermal hysteresis) has led to the idea that frost-sensitive crop plants could avoid damage resulting from common minor frost events in late spring and early autumn by expressing high activity AFPs that permit them to remain unfrozen to temperatures of approximately -5 degrees C. Over the past 20 years, the efficacy of this concept has been tested in a variety of studies that produced transgenic plants (including Arabidopsis thaliana, and several crop plants) expressing various AFPs. Initially, fish AFPs were employed in these studies but as insect AFPs, with higher levels of antifreeze activity, were discovered these have become the AFPs of choice in plant transformation studies. Some studies have produced transgenic plants that have exhibited improved cold tolerance of 1-3 degrees C compared to the wild-type. None of the studies with transgenic plants, however, have yet attained a sufficient level of protection. Progress to this point indicates that more significant results are achievable. If so, the billions of dollars lost annually to frost damage of sensitive crops could be avoided. Geographic ranges and growing seasons could also be expanded. This review provides an overview of the studies of transgenic plants producing AFPs, and makes suggestions for future advancements in this field of study. (C) 2014 Elsevier B.V. All rights reserved.