title: Transgenic barley grain overexpressing thioredoxin shows evidence that the starchy endosperm communicates with the embryo and the aleurone.
abstract: Homozygous lines of barley overexpressing a wheat thioredoxin h transgene (up to 30-fold) were generated earlier by using a B(1)-hordein promoter with a signal peptide sequence for targeting to the protein body and found to be enriched in starch debranching enzyme (pullulanase). Here, we describe the effect of biochemically active, overexpressed thioredoxin h on germination and the onset of alpha-amylase activity. Relative to null segregant controls lacking the transgene, homozygotes overexpressing thioredoxin h effected (i) an acceleration in the rate of germination and appearance of alpha-amylase activity with a 1.6- to 2.8-fold increase in gibberellin A(1) (GA(1)) content; (ii) a similar acceleration in the appearance of the alpha-amylase activity in deembryonated transgenic grain incubated with gibberellic acid; (iii) a 35% increase in the ratio of relative reduction (abundance of SH) of the propanol soluble proteins (hordein I fraction); and (iv) an increase in extractable and soluble protein of 5-12% and 11-35%, respectively. Thioredoxin h, which was highly reduced in the dry grain, was degraded in both the null segregant and homozygote after imbibition. The increase in alpha-amylase activity and protein reduction status was accompanied by a shift in the distribution of protein from the insoluble to the soluble fraction. The results provide evidence that thioredoxin h of the starchy endosperm communicates with adjoining tissues, thereby regulating their activities, notably by accelerating germination of the embryo and the appearance of alpha-amylase released by the aleurone.
authors.affiliation: Department of Plant and Microbial Biology, University of California, 111 Koshland Hall, Berkeley, CA 94720, USA.
authors.forename: Joshua H
authors.initials: JH
authors.lastname: Wong
authors.forename: Yong-Bum
authors.initials: YB
authors.lastname: Kim
authors.forename: Pei-Hsien
authors.initials: PH
authors.lastname: Ren
authors.forename: Nick
authors.initials: N
authors.lastname: Cai
authors.forename: Myeong-Je
authors.initials: MJ
authors.lastname: Cho
authors.forename: Peter
authors.initials: P
authors.lastname: Hedden
authors.forename: Peggy G
authors.initials: PG
authors.lastname: Lemaux
authors.forename: Bob B
authors.initials: BB
authors.lastname: Buchanan
mesh_terms: D003890:Desiccation; D004790:Enzyme Induction; D018525:Germination; D005875:Gibberellins / Q000494:pharmacology; D005983:Glutens; D006720:Homozygote; D001467:Hordeum / Q000196:embryology / Q000378:metabolism*; D010084:Oxidation-Reduction; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012639:Seeds / Q000201:enzymology* / Q000254:growth & development / Q000648:ultrastructure; D013213:Starch / Q000378:metabolism; D054480:Thioredoxin h; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism*; D019076:Transgenes; D014908:Triticum / Q000201:enzymology* / Q000235:genetics; D000516:alpha-Amylases / Q000378:metabolism
chemical_list: D005875:Gibberellins; D010940:Plant Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D054480:Thioredoxin h; D013879:Thioredoxins; D005983:Glutens; D013213:Starch; C007842:gibberellic acid; D000516:alpha-Amylases