Expression of protein disulfide isomerase is elevated in the endosperm of the maize floury-2 mutant.
A maize protein disulfide isomerase (PDI, EC 5.3.4.1) cDNA clone was isolated and characterized. The deduced amino acid sequence contains two regions characteristic of the active sites for PDI and a carboxyl-terminal endoplasmic reticulum (ER) retention sequence, Lys-Asp-Glu-Leu. Southern blot analysis indicated the maize PDI is encoded by a single gene that maps to the short arm of chromosome 4. When isolated from the cisternal and protein body ER, the PDI protein resolves into a fast and a slow form on SDS-PAGE. During endosperm development, the PDI RNA level increases between 10 and 14 days after pollination. In floury-2 (fl2) endosperm, which contains an abnormally processed alpha-zein protein, PDI expression is significantly increased, and the level of PDI protein and RNA is positively correlated with the dosage of fl2 alleles. The increase of PDI in fl2 occurs mainly in the cisternal ER fraction, whereas the most dramatic increase of binding protein (BiP) is in the protein body ER. We propose that the induction of PDI in the fl2 mutant reflects its role as a molecular chaperone, and that PDI functions in concert with BiP at different stages of zein processing and assembly into protein bodies.
Li
C P
CP
Department of Plant Sciences, University of Arizona, Tucson, 85721, USA.
Larkins
B A
BA
D000595:Amino Acid Sequence; D001483:Base Sequence; D018076:DNA, Complementary; D018628:Gene Dosage; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D007527:Isoenzymes / Q000235:genetics*; D007535:Isomerases / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D019704:Protein Disulfide-Isomerases; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000201:enzymology; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics
D018076:DNA, Complementary; D007527:Isoenzymes; D007535:Isomerases; D019704:Protein Disulfide-Isomerases