Regulation of starch accumulation by granule-associated plant 14-3-3 proteins.
In higher plants the production of starch is orchestrated by chloroplast-localized biosynthetic enzymes, namely starch synthases, ADP-glucose pyrophosphorylase, and starch branching and debranching enzymes. Diurnal regulation of these enzymes, as well as starch-degrading enzymes, influences both the levels and composition of starch, and is dependent in some instances upon phosphorylation-linked regulation. The phosphoserine/threonine-binding 14-3-3 proteins participate in environmentally responsive phosphorylation-related regulatory functions in plants, and as such are potentially involved in starch regulation. We report here that reduction of the epsilon subgroup of Arabidopsis 14-3-3 proteins by antisense technology resulted in a 2- to 4-fold increase in leaf starch accumulation. Dark-governed starch breakdown was unaffected in these "antisense plants," indicating an unaltered starch-degradation pathway and suggesting a role for 14-3-3 proteins in regulation of starch synthesis. Absorption spectra and gelatinization properties indicate that the starch from the antisense plants has an altered branched glucan composition. Biochemical characterization of protease-treated starch granules from both Arabidopsis leaves and maize endosperm showed that 14-3-3 proteins are internal intrinsic granule proteins. These data suggest a direct role for 14-3-3 proteins in starch accumulation. The starch synthase III family is a possible target for 14-3-3 protein regulation because, uniquely among plastid-localized starch metabolic enzymes, all members of the family contain the conserved 14-3-3 protein phosphoserine/threonine-binding consensus motif. This possibility is strengthened by immunocapture using antibodies to DU1, a maize starch synthase III family member, and direct interaction with biotinylated 14-3-3 protein, both of which demonstrated an association between 14-3-3 proteins and DU1 or DU1-like proteins.
Sehnke
P C
PC
Program in Plant Molecular and Cellular Biology, Department of Horticultural Sciences, University of Florida, Gainesville, FL 32611, USA..
Chung
H J
HJ
Wu
K
K
Ferl
R J
RJ
D048948:14-3-3 Proteins; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D001665:Binding Sites; D019921:Biotinylation; D002736:Chloroplasts / Q000378:metabolism*; D016384:Consensus Sequence; D003594:Cytoplasmic Granules / Q000502:physiology*; D016373:DNA, Antisense / Q000494:pharmacology; D018076:DNA, Complementary / Q000235:genetics; D003624:Darkness; D005964:Glucosyltransferases / Q000378:metabolism; D046911:Macromolecular Substances; D016253:Microscopy, Immunoelectron; D010766:Phosphorylation; D010940:Plant Proteins / Q000502:physiology*; D030821:Plants, Genetically Modified; D011485:Protein Binding; D012639:Seeds; D011198:Solanum tuberosum / Q000378:metabolism; D013045:Species Specificity; D013213:Starch / Q000378:metabolism*; D014908:Triticum / Q000378:metabolism; D014446:Tyrosine 3-Monooxygenase / Q000502:physiology*; D003313:Zea mays / Q000201:enzymology
D048948:14-3-3 Proteins; D016373:DNA, Antisense; D018076:DNA, Complementary; D046911:Macromolecular Substances; D010940:Plant Proteins; D013213:Starch; D014446:Tyrosine 3-Monooxygenase; D005964:Glucosyltransferases; C412710:starch synthase III, Triticum aestivum