title: Asparagus Spears as a Model to Study Heteroxylan Biosynthesis during Secondary Wall Development.
abstract: Garden asparagus (Asparagus officinalis L.) is a commercially important crop species utilized for its excellent source of vitamins, minerals and dietary fiber. However, after harvest the tissue hardens and its quality rapidly deteriorates because spear cell walls become rigidified due to lignification and substantial increases in heteroxylan content. This latter observation prompted us to investigate the in vitro xylan xylosyltransferase (XylT) activity in asparagus. The current model system for studying heteroxylan biosynthesis, Arabidopsis, whilst a powerful genetic system, displays relatively low xylan XylT activity in in vitro microsomal preparations compared with garden asparagus therefore hampering our ability to study the molecular mechanism(s) of heteroxylan assembly. Here, we analyzed physiological and biochemical changes of garden asparagus spears stored at 4 °C after harvest and detected a high level of xylan XylT activity that accounts for this increased heteroxylan. The xylan XylT catalytic activity is at least thirteen-fold higher than that reported for previously published species, including Arabidopsis and grasses. A biochemical assay was optimized and up to seven successive Xyl residues were incorporated to extend the xylotetraose (Xyl4) acceptor backbone. To further elucidate the xylan biosynthesis mechanism, we used RNA-seq to generate an Asparagus reference transcriptome and identified five putative xylan biosynthetic genes (AoIRX9, AoIRX9-L, AoIRX10, AoIRX14_A, AoIRX14_B) with AoIRX9 having an expression profile that is distinct from the other genes. We propose that Asparagus provides an ideal biochemical system to investigate the biochemical aspects of heteroxylan biosynthesis and also offers the additional benefit of being able to study the lignification process during plant stem maturation.
authors.affiliation: Nurturing Station for the State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University, Lin'an, Hangzhou, 311300, P. R. China; ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Lili
authors.initials: L
authors.lastname: Song
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Wei
authors.initials: W
authors.lastname: Zeng
authors.affiliation: College of Forestry, South China Agricultural University, Guangzhou, 510642, China.
authors.forename: Aimin
authors.initials: A
authors.lastname: Wu
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Kelsey
authors.initials: K
authors.lastname: Picard
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Edwin R
authors.initials: ER
authors.lastname: Lampugnani
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Roshan
authors.initials: R
authors.lastname: Cheetamun
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Cherie
authors.initials: C
authors.lastname: Beahan
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Cassin
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Lonsdale
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Monika S
authors.initials: MS
authors.lastname: Doblin
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, School of Botany, the University of Melbourne, Parkville, VIC 3010, Australia; Bio21 Molecular Science and Biotechnology Institute, the University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Antony
authors.initials: A
authors.lastname: Bacic
mesh_terms: D017360:Arabidopsis / Q000378:metabolism; D027761:Asparagus Plant / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D018533:Biomass; D053898:Biosynthetic Pathways / Q000235:genetics; D002473:Cell Wall / Q000378:metabolism*; D003080:Cold Temperature; D005456:Fluorescent Dyes / Q000378:metabolism; D017343:Genes, Plant; D001467:Hordeum / Q000378:metabolism; D008031:Lignin / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D010430:Pentosyltransferases; D013045:Species Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013997:Time Factors; D014990:Xylans / Q000096:biosynthesis*; D000097608:UDP Xylose-Protein Xylosyltransferase
chemical_list: D005456:Fluorescent Dyes; D008031:Lignin; D010430:Pentosyltransferases; D014990:Xylans; D000097608:UDP Xylose-Protein Xylosyltransferase