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Synthesis, processing and export of cytoplasmic endo-ß-1,4-xylanase from barley aleurone during germination

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Author: Caspers, M.P.M. · Lok, F. · Sinjorgo, K.M.C. · Zeijl, M. van · Nielsen, K.A. · Cameron-Mills, V.
Type:article
Date:2001
Institution: Centraal Instituut voor Voedingsonderzoek TNO
Source:The Plant Journal, 2, 26, 191-204
Identifier: 72511
doi: doi:10.1046/j.0960-7412.2001.01019.x
Keywords: Nutrition · Amino Acid Sequence · Apoptosis · Blotting, Western · Cysteine Endopeptidases · Cytoplasm · Endo-1,4-beta Xylanases · Gene Expression Regulation, Plant · Genes, Plant · Germination · Green Fluorescent Proteins · Hordeum · Hydrolases · Indicators and Reagents · Luminescent Proteins · Microscopy, Confocal · Molecular Sequence Data · Molecular Weight · Plant Proteins · Protoplasts · RNA Precursors · Seeds · Starch · Xylosidases · Hordeum vulgare subsp. vulgare

Abstract

We have identified the major endo-β-l,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. Chemicals/CAS: alpha-Amylase, EC 3.2.1.1; Cysteine Endopeptidases, EC 3.4.22.-; Endo-1,4-beta Xylanases, EC 3.2.1.8; Green Fluorescent Proteins, 147336-22-9; Hydrolases, EC 3.-; Indicators and Reagents; Luminescent Proteins; Plant Proteins; RNA Precursors; Starch, 9005-25-8; Xylosidases, EC 3.2.1.-