Constitutive Freezing Tolerant Mutants in Arabidopsis

Abstract

Little is known about the signaling cascades by which plants perceive low temperatures and use the information to trigger molecular and biochemical programs leading to increased freezing tolerance. We have developed a Petri dish freezing assay that allows rapid screening of large numbers of M2 plants for mutants which are constitutively freezing tolerant. In this assay, non-acclimated wild-type Arabidopsis thaliana, Columbia exhibited a killing temperature (LT50) of −5.3°C. Two days of acclimation at 4°C brought about a change in LT50 to −12°C. Over 20 independent mutant lines that are freezing tolerant without cold acclimation were obtained by screening approximately 800,000 EMS-mutagenized M2 plants at −8°C. One mutant line, which has a recessive mutation at a locus designated eskimol (esk1), has LT50 of-11.5°C in the absence of acclimation. The esk1 mutant is smaller than WT but in most other aspects the growth and development of these plants are similar to WT. One hypothesis to explain the recessiveness and pleiot-ropic effects of esk1 is that the wild-type ESK1 gene may encode a negative regulator which represses the genetic programs required to withstand freezing at normal growth conditions.