Abstract
Many plants acquire increased freezing tolerance when they are exposed to nonfreezing temperatures of a certain duration. This process is known as cold acclimation and allows plants to protect themselves from freezing injury. A wide variety of polypeptides are induced during cold acclimation, among which is one encoded by COR15A in Arabidopsis. Previous studies showed that the COR15A gene encodes a small, plastid-targeted polypeptide that is processed to a mature form called Cor15am. Here, we examined the biochemical properties and activities of Cor15am in more detail. We provide evidence that Cor15am localizes almost exclusively to the chloroplast stroma. In addition, the cold-regulated accumulation of Cor15am is affected by chloroplasts. Recombinant Cor15am exhibits in vitro cryoprotection of a freeze-labile enzyme, L-lactate dehydrogenase by direct association to the substrate. On the basis of these results, we will discuss physiological roles of Cor15am under cold stress.
