Genetic and biochemical evidence for the involvement of alpha-1,4 glucanotransferases in amylopectin synthesis

We describe a novel mutation in the Chlamydomonas reinhardtii STA11 gene, w hich results in significantly reduced granular starch deposition and major modifications in amylopectin structure and granule shape. This defect simul taneously leads to the accumulation of linear malto-oligosaccharides. The s ta11-1 mutation causes the absence of an alpha-1,4 glucanotransferase known as disproportionating enzyme (D-enzyme). D-enzyme activity was found to be correlated with the amount of wild-type allele doses in gene dosage experi ments. All other enzymes involved in starch biosynthesis, including ADP-glu cose pyrophosphorylase, debranching enzymes, soluble and granule-bound star ch synthases, branching enzymes, phosphorylases, cu-glucosidases (maltases) , and amylases, were unaffected by the mutation. These data indicate that t he D-enzyme is required for normal starch granule biogenesis in the monocel lular alga C. reinhardtii.