Gene expression in a starch synthase IIa mutant of barley: changes in the level of gene transcription and grain composition.

The barley shrunken grain mutant M292 has a novel high-amylose starch phenotype caused by a mutation in the starch synthase IIa gene (SsIIa) located at the starch excess-6 (sex6) locus on chromosome 7H of barley. The loss of SSIIa enzyme activity leads to a decrease in amylopectin synthesis to less than 20% of the levels found in wild-type grains. Detailed composition analysis indicates that the contents of protein, non-starch polysaccharides, lipid, sucrose and hexoses, and fructo-oligosaccharides are increased in mature M292 grain compared to wild type. Using a microarray analysis, we characterize the differences between the transcription profiles of wild-type and mutant barley endosperms at mid-grain fill. The expression changes include genes involved in carbon storage, stress-related genes, and a number of transcripts with unassigned function. The changes in gene expression are discussed in terms of the altered grain composition of the mutant seed.