eskimo1mutants ofArabidopsisare constitutively freezing-tolerant

Abstract

Temperate plants develop a greater ability to withstand freezing in response to a period of low but nonfreezing temperatures through a complex, adaptive process of cold acclimation. Very little is known about the signaling processes by which plants perceive the low temperature stimulus and transduce it into the nucleus to activate genes needed for increased freezing tolerance. To help understand the signaling processes, we have isolated mutants of Arabidopsis that are constitutively freezing-tolerant in the absence of cold acclimation. Freezing tolerance of wild-type Arabidopsis was increased from ؊5.5°C to ؊12.6°C by cold acclimation whereas the freezing tolerance of 26 mutant lines ranged from ؊6.8°C to ؊10.6°C in the absence of acclimation. Plants with mutations at the eskimo1 (esk1) locus accumulated high levels of proline, a compatible osmolyte, but did not exhibit constitutively increased expression of several cold-regulated genes involved in freezing tolerance. RNA gel blot analysis suggested that proline accumulation in esk1 plants was mediated by regulation of transcript levels of genes involved in proline synthesis and degradation. The characterization of esk1 mutants and results from other mutants suggest that distinct signaling pathways activate different aspects of cold acclimation and that activation of one pathway can result in considerable freezing tolerance without activation of other pathways.

Overexpression of the Arabidopsis 10-Kilodalton Acyl-Coenzyme A-Binding Protein ACBP6 Enhances Freezing Tolerance

“…The constitutive expression of the transcriptional activator CBF1/DREB1B enhanced freezing tolerance (Jaglo-Ottosen et al, 1998), while DREB1A overexpression improved drought, salt, and freezing tolerance in transgenic Arabidopsis (Kasuga et al, 1999). Besides the transcriptional regulatory pathway mediated by DREB activators (for review, see YamaguchiShinozaki andShinozaki, 2005, 2006), other independent pathways leading to freezing tolerance have been proposed (Xin and Browse, 1998;Welti et al, 2002;.…”

A DEAD Box RNA Helicase Is Critical for Pre-mRNA Splicing, Cold-Responsive Gene Regulation, and Cold Tolerance inArabidopsis

“…As shown in Figures 1C and 1D, hypocotyl elongation was similar for rcf1-1 and the wild type at 21°C but was dramatically less for rcf1-1 than for the wild type at 4°C, indicating that normal function of RCF1 is required for chilling stress tolerance. We subsequently determined the freezing tolerance of rcf1-1 by two methods: an electrolyte leakage assay (Sukumaran and Weiser, 1972;Ishitani et al, 1998) and a whole-plant freezing assay (Warren et al, 1996;JagloOttosen et al, 1998;Xin and Browse, 1998;Zhu et al, 2008). The rcf1-1 plants were hypersensitive to freezing temperatures before and after cold acclimation (Figures 1E to 1G), indicating that the ability to be fully acclimated is substantially reduced in rcf1-1.…”

The SENSITIVE TO FREEZING2 Gene, Required for Freezing Tolerance in Arabidopsis thaliana, Encodes a β-Glucosidase

“…In one study, mutants were obtained that caused elevated levels of freezing tolerance in the absence of cold acclimation (Xin and Browse, 1998). The mutations may point to components of the signaling pathway(s) that are responsible for cold acclimation or identify genes that can make self-sufficient individual contributions to freeze protection.…”