Synthesis, processing and export of cytoplasmic endo-beta-1,4-xylanase from barley aleurone during germination.
We have identified the major endo-beta-1,4-xylanase (XYN-1) in the aleurone of germinating barley grain, and show that it is expressed as a precursor of Mr 61 500 with both N- and C-terminal propeptides. XYN-1 is synthesized as an inactive enzyme in the cytoplasm, and only becomes active at a late stage of germination when the aleurone ceases to secrete hydrolases. A series of processing steps, mediated in part by aleurone cysteine endoproteases, yields a mature active enzyme of Mr 34 000. Processing and extracellular release of the mature enzyme coincide with the programmed cell death (PCD)-regulated disintegration of aleurone cells. We discuss the significance of delayed aleurone cell-wall degradation by endoxylanases in relation to the secretory capacity of the aleurone, and propose a novel role for aleurone PCD in facilitating the export of hydrolases.
Caspers
M P
MP
Department of Applied Plant Sciences, TNO Nutrition and Food Research Institute, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands, and; Carlsberg Research Laboratory, Gamle Carlsberg Vej 10, DK-2500 Copenhagen, Denmark.
Lok
F
F
Sinjorgo
K M
KM
van Zeijl
M J
MJ
Nielsen
K A
KA
Cameron-Mills
V
V
D000595:Amino Acid Sequence; D017209:Apoptosis; D015153:Blotting, Western; D003546:Cysteine Endopeptidases / Q000378:metabolism; D003593:Cytoplasm / Q000201:enzymology; D043364:Endo-1,4-beta Xylanases; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018525:Germination / Q000502:physiology; D049452:Green Fluorescent Proteins; D001467:Hordeum / Q000196:embryology / Q000378:metabolism*; D006867:Hydrolases / Q000378:metabolism; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010940:Plant Proteins; D011523:Protoplasts / Q000166:cytology / Q000378:metabolism; D012322:RNA Precursors; D012639:Seeds / Q000166:cytology / Q000378:metabolism*; D013213:Starch / Q000378:metabolism; D014995:Xylosidases / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D000516:alpha-Amylases / Q000235:genetics / Q000378:metabolism
D007202:Indicators and Reagents; D008164:Luminescent Proteins; D010940:Plant Proteins; D012322:RNA Precursors; D049452:Green Fluorescent Proteins; D013213:Starch; D006867:Hydrolases; D014995:Xylosidases; D000516:alpha-Amylases; D043364:Endo-1,4-beta Xylanases; D003546:Cysteine Endopeptidases