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, andas a result, a large amount of amylose is accumulated causing a reductionin rice grain quality. We found that the seeds of a du mutant couldbe visibly distinguished depending on whether they matured at cool ornormal temperatures. Using these characteristics, we isolated a mutantcandidate insensitive to cool temperatures. While the amylose content inthe original line was about 2% at a normal temperature (28 °C)and 12% at a cool temperature (21 °C), in the mutant candidate(coi) the amylose content was not affected by temperatures, i.e. theamylose content was about 3% at both temperatures. This finding incombination with the results of an immunoblot analysis indicated that theabsence of an increase in the amylose content in this mutant was caused bya constant level of Wx gene expression at normal and cooltemperature. Genetic analysis revealed that this insensitivity to cooltemperatures was caused by a single recessive mutation. This mutantshould be useful in breeding programs designed to produce rice of desiredquality at cool temperatures and in understanding genetic and molecularmechanisms that respond to slight changes in temperature.