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Asparagus Spears as a Model to Study Heteroxylan Biosynthesis during Secondary Wall Development.

Song L, Zeng W, Wu A, Picard K, Lampugnani ER, Cheetamun R, Beahan C, Cassin A, Lonsdale A, Doblin MS, Bacic A - PLoS ONE (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

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.

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.

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Xylan XylT activities of different Asparagus sections over the 4°C storage period.Microsomes from apical, middle and basal sections of Asparagus spears stored at 4°C for 0–16 days were isolated and the XylT activities were measured as described in the Materials and Methods. Data were average values±SE (n = 3).
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pone.0123878.g009: Xylan XylT activities of different Asparagus sections over the 4°C storage period.Microsomes from apical, middle and basal sections of Asparagus spears stored at 4°C for 0–16 days were isolated and the XylT activities were measured as described in the Materials and Methods. Data were average values±SE (n = 3).

Mentions: To investigate changes in xylan XylT activity during the storage process, Asparagus spear tissues from six stages (0, 2, 4, 8, 12, 14 days post-harvest) were collected and the XylT activity of the apical, middle and basal sections was analyzed. The basal tissue was found to have four times higher XylT activity than the apical section in freshly harvested tissues, correlating with the increased heteroxylan content of this section compared to the apex (Fig 9). Notably, the XylT activity slightly increased during the initial stage of storage (0–2 day after harvest) and then declined in all three sections with additional storage time (Fig 9).


Asparagus Spears as a Model to Study Heteroxylan Biosynthesis during Secondary Wall Development.

Song L, Zeng W, Wu A, Picard K, Lampugnani ER, Cheetamun R, Beahan C, Cassin A, Lonsdale A, Doblin MS, Bacic A - PLoS ONE (2015)

Xylan XylT activities of different Asparagus sections over the 4°C storage period.Microsomes from apical, middle and basal sections of Asparagus spears stored at 4°C for 0–16 days were isolated and the XylT activities were measured as described in the Materials and Methods. Data were average values±SE (n = 3).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4404143&req=5

pone.0123878.g009: Xylan XylT activities of different Asparagus sections over the 4°C storage period.Microsomes from apical, middle and basal sections of Asparagus spears stored at 4°C for 0–16 days were isolated and the XylT activities were measured as described in the Materials and Methods. Data were average values±SE (n = 3).
Mentions: To investigate changes in xylan XylT activity during the storage process, Asparagus spear tissues from six stages (0, 2, 4, 8, 12, 14 days post-harvest) were collected and the XylT activity of the apical, middle and basal sections was analyzed. The basal tissue was found to have four times higher XylT activity than the apical section in freshly harvested tissues, correlating with the increased heteroxylan content of this section compared to the apex (Fig 9). Notably, the XylT activity slightly increased during the initial stage of storage (0–2 day after harvest) and then declined in all three sections with additional storage time (Fig 9).

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

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.

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.

Show MeSH