Mutational analysis of the pullulanase-type debranching enzyme of maize indicates multiple functions in starch metabolism.
Plants contain two types of alpha(1-->6) glucan hydrolase (starch-debranching enzyme [DBE]). Mutations that affect the pullulanase-type DBE have not been described, although defects in isoamylase-type DBE, known in many plant species, indicate a function in starch biosynthesis. We describe a null mutation of a pullulanase-type DBE gene, a Mutator insertion in maize Zpu1. Plants homozygous for the zpu1-204 mutation are impaired in transient and storage starch degradation. Thus, hydrolytic activity of pullulanase-type DBE contributes to starch catabolism. Developing zpu1-204 endosperm accumulates branched maltooligosaccharides not found in the wild type and is deficient in linear maltooligosaccharides, indicating that the pullulanase-type DBE functions in glucan hydrolysis during kernel starch formation. Furthermore, in a background deficient in isoamylase-type DBE, zpu1-204 conditions a significant accumulation of phytoglycogen in the kernel that is not seen in the wild type. Therefore, pullulanase-type DBE partially compensates for the defect in isoamylase-type DBE, suggesting a function during starch synthesis as well as degradation.
Dinges
Jason R
JR
Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA.
Colleoni
Christophe
C
James
Martha G
MG
Myers
Alan M
AM
D000483:Alleles; D000595:Amino Acid Sequence; D018525:Germination / Q000502:physiology; D006026:Glycoside Hydrolases / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000378:metabolism; D013213:Starch / Q000096:biosynthesis* / Q000378:metabolism; D003313:Zea mays / Q000201:enzymology / Q000235:genetics*
D010940:Plant Proteins; D013213:Starch; D006026:Glycoside Hydrolases; C118576:ZPU1 protein, Zea mays