Isolation and characterization of a rice mutant insensitive to cool temperatures on amylose synthesis

The Wx(b) gene, one of the alleles at the rice waxy (wx) locus, is activated at cool temperatures during seed development, and as a result, a large amount of amylose is accumulated causing a reduction in rice grain quality. We found that the seeds of a du mutant could be visibly distinguished depending on whether they matured at cool or normal temperatures. Using these characteristics, we isolated a mutant candidate insensitive to cool temperatures. While the amylose content in the original line was about 2% at a normal temperature (28 degreesC) and 12% at a cool temperature (21 degreesC), in the mutant candidate (coi) the amylose content was not affected by temperatures, i.e. the amylose content was about 3% at both temperatures. This finding in combination with the results of an immunoblot analysis indicated that the absence of an increase in the amylose content in this mutant was caused by a constant level of Wx gene expression at normal and cool temperature. Genetic analysis revealed that this insensitivity to cool temperatures was caused by a single recessive mutation. This mutant should be useful in breeding programs designed to produce rice of desired quality at cool temperatures and in understanding genetic and molecular mechanisms that respond to slight changes in temperature.