Molecular mechanism of acclimation and tolerance to low temperature.

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(1) The effect of unsaturated membrane lipids on tolerance to cold and freezing stress : Up to the last year we demonstrated that unsaturated membrane lipids protect the photosynthetic machinery of plants and cyanobacteria against the photoinhibition at low temperature by promoting the repair of photoinhibited photosystem II.In this year, we have elucidated that the unsaturated membrane lipids accelerate the translation of psbA gene for the precursor to D1 protein, and furthermore that they are also important in the tolerance of the photosynthetic machinery to salt stress.(2) Protection against cold and freezing stress by glycinebetaine : We previously demonstrated that the genetic manipulation to enable Arabidopsis to synthesize glycinebetaine enhances tolerance to various kinds of environmental stress at various stages of life cycle. In this year we have elucidated that the protective effect of glycinebetaine is based on the promotion of protein synthesis de novo by stabilizing the protein-synthesizing machinery.(3) New factors for cold acclimation : The global examination of cold-inducible expression of genes in Synechocystis with DNA microarrays has revealed that cold stress induces a number of genes, which encode factors in transcription and translation, subunit proteins of ribosomes, RNA helicases, and a number of proteins of unknown function. Functions of these proteins in cold acclimation are important subjects of future study.(4) Cold sensor and cold signal transduction pathway : Up to the last year, we identified two cold sensors and a cold-signal transducer. In this year, we have applied DNA microarrays to successfully classify cold-inducible genes into three groups according to the regulation of cold inducibility by the cold sensors. Group-1 genes are regulated by the first cold sensor, Group-2 genes are by the second sensor, and Group-3 genes are by both sensors.