title: Functions of heteromeric and homomeric isoamylase-type starch-debranching enzymes in developing maize endosperm.
abstract: Functions of isoamylase-type starch-debranching enzyme (ISA) proteins and complexes in maize (Zea mays) endosperm were characterized. Wild-type endosperm contained three high molecular mass ISA complexes resolved by gel permeation chromatography and native-polyacrylamide gel electrophoresis. Two complexes of approximately 400 kD contained both ISA1 and ISA2, and an approximately 300-kD complex contained ISA1 but not ISA2. Novel mutations of sugary1 (su1) and isa2, coding for ISA1 and ISA2, respectively, were used to develop one maize line with ISA1 homomer but lacking heteromeric ISA and a second line with one form of ISA1/ISA2 heteromer but no homomeric enzyme. The mutations were su1-P, which caused an amino acid substitution in ISA1, and isa2-339, which was caused by transposon insertion and conditioned loss of ISA2. In agreement with the protein compositions, all three ISA complexes were missing in an ISA1-null line, whereas only the two higher molecular mass forms were absent in the ISA2-null line. Both su1-P and isa2-339 conditioned near-normal starch characteristics, in contrast to ISA-null lines, indicating that either homomeric or heteromeric ISA is competent for starch biosynthesis. The homomer-only line had smaller, more numerous granules. Thus, a function of heteromeric ISA not compensated for by homomeric enzyme affects granule initiation or growth, which may explain evolutionary selection for ISA2. ISA1 was required for the accumulation of ISA2, which is regulated posttranscriptionally. Quantitative polymerase chain reaction showed that the ISA1 transcript level was elevated in tissues where starch is synthesized and low during starch degradation, whereas ISA2 transcript was relatively abundant during periods of either starch biosynthesis or catabolism.
authors.affiliation: Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Akiko
authors.initials: A
authors.lastname: Kubo
authors.forename: Christophe
authors.initials: C
authors.lastname: Colleoni
authors.forename: Jason R
authors.initials: JR
authors.lastname: Dinges
authors.forename: Qiaohui
authors.initials: Q
authors.lastname: Lin
authors.forename: Ryan R
authors.initials: RR
authors.lastname: Lappe
authors.forename: Joshua G
authors.initials: JG
authors.lastname: Rivenbark
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Meyer
authors.forename: Steven G
authors.initials: SG
authors.lastname: Ball
authors.forename: Martha G
authors.initials: MG
authors.lastname: James
authors.forename: Tracie A
authors.initials: TA
authors.lastname: Hennen-Bierwagen
authors.forename: Alan M
authors.initials: AM
authors.lastname: Myers
mesh_terms: D050260:Carbohydrate Metabolism; D002850:Chromatography, Gel; D056625:Endosperm / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D018525:Germination / Q000235:genetics; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism*; D007517:Isoamylase / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010936:Plant Extracts; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013213:Starch / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*
chemical_list: D010936:Plant Extracts; D010940:Plant Proteins; D012333:RNA, Messenger; D013213:Starch; D006026:Glycoside Hydrolases; C118576:ZPU1 protein, Zea mays; D007517:Isoamylase
references.citation: J Biol Chem. 2006 Apr 28;281(17):12050-9
references.pmid: 16495218
references.citation: Nat Protoc. 2009;4(3):363-71
references.pmid: 19247286
references.citation: Plant Cell. 2008 Dec;20(12):3448-66
references.pmid: 19074683
references.citation: Plant Physiol. 1999 Jan;119(1):255-66
references.pmid: 9880368
references.citation: Biosci Biotechnol Biochem. 2007 Sep;71(9):2308-12
references.pmid: 17827690
references.citation: Plant Physiol. 1994 Jan;104(1):179-87
references.pmid: 8115545
references.citation: Proc Natl Acad Sci U S A. 2001 Sep 25;98(20):11479-84
references.pmid: 11562485
references.citation: Plant Cell. 2003 Mar;15(3):666-80
references.pmid: 12615940
references.citation: Plant J. 2005 Mar;41(6):815-30
references.pmid: 15743447
references.citation: Biochem J. 1991 Nov 15;280 ( Pt 1):51-5
references.pmid: 1741756
references.citation: Plant Cell. 1998 Oct;10(10):1699-712
references.pmid: 9761796
references.citation: Genetics. 2008 Apr;178(4):2373-87
references.pmid: 18245855
references.citation: Proc Natl Acad Sci U S A. 1984 Dec;81(24):8014-8
references.pmid: 6096873
references.citation: Cell. 1996 Aug 9;86(3):349-52
references.pmid: 8756717
references.citation: Plant Physiol. 1998 Jun;117(2):425-35
references.pmid: 9625695
references.citation: Plant Cell. 2003 Jan;15(1):133-49
references.pmid: 12509527
references.citation: Proc Natl Acad Sci U S A. 2004 Feb 17;101(7):2215-20
references.pmid: 14766984
references.citation: Planta. 2006 Dec;225(1):75-87
references.pmid: 16953433
references.citation: Plant Physiol. 2008 Apr;146(4):1892-908
references.pmid: 18281416
references.citation: Genetics. 1947 Sep;32(5):448-58
references.pmid: 17247255
references.citation: J Protein Chem. 1993 Dec;12(6):791-805
references.pmid: 8136030
references.citation: Genetics. 1947 Sep;32(5):459-85
references.pmid: 17247256
references.citation: Plant Cell. 1995 Jan;7(1):75-84
references.pmid: 7696880
references.citation: Plant Cell. 1995 Apr;7(4):417-29
references.pmid: 7773016
references.citation: Plant Physiol. 1999 Oct;121(2):399-410
references.pmid: 10517831
references.citation: Plant Physiol. 2001 Mar;125(3):1406-18
references.pmid: 11244120
references.citation: Planta. 1999 Apr;208(2):283-93
references.pmid: 10333591
references.citation: Plant Physiol. 2005 May;138(1):184-95
references.pmid: 15849301
references.citation: Nucleic Acids Res. 1995 Jul 11;23(13):2569-70
references.pmid: 7630740
references.citation: Theor Appl Genet. 2009 Sep;119(5):815-25
references.pmid: 19593540
references.citation: Plant Cell Physiol. 2002 Jul;43(7):718-25
references.pmid: 12154134
references.citation: J Mol Biol. 1998 Sep 4;281(5):885-97
references.pmid: 9719642
references.citation: Plant Cell. 1996 Aug;8(8):1353-1366
references.pmid: 12239416
references.citation: Plant Physiol. 2000 Apr;122(4):989-97
references.pmid: 10759494
references.citation: Plant Physiol. 2008 Nov;148(3):1309-23
references.pmid: 18815382
references.citation: Plant J. 2002 Jul;31(1):97-112
references.pmid: 12100486