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Discovery of diversity in xylan biosynthetic genes by transcriptional profiling of a heteroxylan containing mucilaginous tissue.

Jensen JK, Johnson N, Wilkerson CG - Front Plant Sci (2013)

Bottom Line: This tissue was found to have high expression levels of an IRX10 homolog, but very low levels of the two GT43 family members.This contrasts with recent wheat endosperm tissue profiling that found a relatively high abundance of the GT43 family members.The numerous GT61 family members also show a wide sequence diversity and may be responsible for the larger number of side chain structures present in the psyllium mucilage.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, Michigan State University East Lansing, MI, USA ; DOE Great Lakes Bioenergy Research Center, Michigan State University East Lansing, MI, USA.

ABSTRACT
The exact biochemical steps of xylan backbone synthesis remain elusive. In Arabidopsis, three non-redundant genes from two glycosyltransferase (GT) families, IRX9 and IRX14 from GT43 and IRX10 from GT47, are candidates for forming the xylan backbone. In other plants, evidence exists that different tissues express these three genes at widely different levels, which suggests that diversity in the makeup of the xylan synthase complex exists. Recently we have profiled the transcripts present in the developing mucilaginous tissue of psyllium (Plantago ovata Forsk). This tissue was found to have high expression levels of an IRX10 homolog, but very low levels of the two GT43 family members. This contrasts with recent wheat endosperm tissue profiling that found a relatively high abundance of the GT43 family members. We have performed an in-depth analysis of all GTs genes expressed in four developmental stages of the psyllium mucilagenous layer and in a single stage of the psyllium stem using RNA-Seq. This analysis revealed several IRX10 homologs, an expansion in GT61 (homologs of At3g18170/At3g18180), and several GTs from other GT families that are highly abundant and specifically expressed in the mucilaginous tissue. Our current hypothesis is that the four IRX10 genes present in the mucilagenous tissues have evolved to function without the GT43 genes. These four genes represent some of the most divergent IRX10 genes identified to date. Conversely, those present in the psyllium stem are very similar to those in other eudicots. This suggests these genes are under selective pressure, likely due to the synthesis of the various xylan structures present in mucilage that has a different biochemical role than that present in secondary walls. The numerous GT61 family members also show a wide sequence diversity and may be responsible for the larger number of side chain structures present in the psyllium mucilage.

No MeSH data available.


Cell wall analysis of psyllium aerial tissues. (A) Neutral monosaccharide composition of total cell walls from various tissues from psyllium (Po) leaves, inflorescent, stem and trichomes and Arabidopsis (At) stem. (B–D) Toluidine blue staining of free-hand sections of psyllium inflorescence (B), stem top (C) and stem bottom (D). (E) Neutral monosaccharide composition of 1 M KOH extractions of various tissues from psyllium leaves, inflorescent, stem top and stem bottom, and Arabidopsis stems bottom. The selected tissues were subjected to sequential extractions with CDTA, Na2CO3 and 1 M KOH.
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Figure 1: Cell wall analysis of psyllium aerial tissues. (A) Neutral monosaccharide composition of total cell walls from various tissues from psyllium (Po) leaves, inflorescent, stem and trichomes and Arabidopsis (At) stem. (B–D) Toluidine blue staining of free-hand sections of psyllium inflorescence (B), stem top (C) and stem bottom (D). (E) Neutral monosaccharide composition of 1 M KOH extractions of various tissues from psyllium leaves, inflorescent, stem top and stem bottom, and Arabidopsis stems bottom. The selected tissues were subjected to sequential extractions with CDTA, Na2CO3 and 1 M KOH.

Mentions: In order to compare xylan biosynthesis in the ML with xylan formation in other tissues of psyllium we first determined the neutral monosaccharide composition for different aerial parts of the plant (Figure 1A). The psyllium stem and inflorescence yielded the highest levels of xylose, which were at levels comparable to Arabidopsis stem. Given glucose levels are low in these tissues, the high levels of xylose likely result from xylan as opposed to xyloglucan. Anatomical investigation by hand sectioning and toluidine blue staining verified the presence of secondary cell wall formation in both inflorescence and stem (Figures 1B–D). Subsequently, a series of sequential extractions, using CDTA, Na2CO3 and KOH, were performed and the xylan enriched 1 M KOH fraction was subjected to neutral monosaccharide composition analysis (Figure 1E). Only minor differences were found in the monosaccharide profiles between Arabidopsis lower stem, psyllium inflorescence and psyllium stem samples. Based on these analyses we chose to profile the transcriptome of psyllium stem.


Discovery of diversity in xylan biosynthetic genes by transcriptional profiling of a heteroxylan containing mucilaginous tissue.

Jensen JK, Johnson N, Wilkerson CG - Front Plant Sci (2013)

Cell wall analysis of psyllium aerial tissues. (A) Neutral monosaccharide composition of total cell walls from various tissues from psyllium (Po) leaves, inflorescent, stem and trichomes and Arabidopsis (At) stem. (B–D) Toluidine blue staining of free-hand sections of psyllium inflorescence (B), stem top (C) and stem bottom (D). (E) Neutral monosaccharide composition of 1 M KOH extractions of various tissues from psyllium leaves, inflorescent, stem top and stem bottom, and Arabidopsis stems bottom. The selected tissues were subjected to sequential extractions with CDTA, Na2CO3 and 1 M KOH.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3675317&req=5

Figure 1: Cell wall analysis of psyllium aerial tissues. (A) Neutral monosaccharide composition of total cell walls from various tissues from psyllium (Po) leaves, inflorescent, stem and trichomes and Arabidopsis (At) stem. (B–D) Toluidine blue staining of free-hand sections of psyllium inflorescence (B), stem top (C) and stem bottom (D). (E) Neutral monosaccharide composition of 1 M KOH extractions of various tissues from psyllium leaves, inflorescent, stem top and stem bottom, and Arabidopsis stems bottom. The selected tissues were subjected to sequential extractions with CDTA, Na2CO3 and 1 M KOH.
Mentions: In order to compare xylan biosynthesis in the ML with xylan formation in other tissues of psyllium we first determined the neutral monosaccharide composition for different aerial parts of the plant (Figure 1A). The psyllium stem and inflorescence yielded the highest levels of xylose, which were at levels comparable to Arabidopsis stem. Given glucose levels are low in these tissues, the high levels of xylose likely result from xylan as opposed to xyloglucan. Anatomical investigation by hand sectioning and toluidine blue staining verified the presence of secondary cell wall formation in both inflorescence and stem (Figures 1B–D). Subsequently, a series of sequential extractions, using CDTA, Na2CO3 and KOH, were performed and the xylan enriched 1 M KOH fraction was subjected to neutral monosaccharide composition analysis (Figure 1E). Only minor differences were found in the monosaccharide profiles between Arabidopsis lower stem, psyllium inflorescence and psyllium stem samples. Based on these analyses we chose to profile the transcriptome of psyllium stem.

Bottom Line: This tissue was found to have high expression levels of an IRX10 homolog, but very low levels of the two GT43 family members.This contrasts with recent wheat endosperm tissue profiling that found a relatively high abundance of the GT43 family members.The numerous GT61 family members also show a wide sequence diversity and may be responsible for the larger number of side chain structures present in the psyllium mucilage.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, Michigan State University East Lansing, MI, USA ; DOE Great Lakes Bioenergy Research Center, Michigan State University East Lansing, MI, USA.

ABSTRACT
The exact biochemical steps of xylan backbone synthesis remain elusive. In Arabidopsis, three non-redundant genes from two glycosyltransferase (GT) families, IRX9 and IRX14 from GT43 and IRX10 from GT47, are candidates for forming the xylan backbone. In other plants, evidence exists that different tissues express these three genes at widely different levels, which suggests that diversity in the makeup of the xylan synthase complex exists. Recently we have profiled the transcripts present in the developing mucilaginous tissue of psyllium (Plantago ovata Forsk). This tissue was found to have high expression levels of an IRX10 homolog, but very low levels of the two GT43 family members. This contrasts with recent wheat endosperm tissue profiling that found a relatively high abundance of the GT43 family members. We have performed an in-depth analysis of all GTs genes expressed in four developmental stages of the psyllium mucilagenous layer and in a single stage of the psyllium stem using RNA-Seq. This analysis revealed several IRX10 homologs, an expansion in GT61 (homologs of At3g18170/At3g18180), and several GTs from other GT families that are highly abundant and specifically expressed in the mucilaginous tissue. Our current hypothesis is that the four IRX10 genes present in the mucilagenous tissues have evolved to function without the GT43 genes. These four genes represent some of the most divergent IRX10 genes identified to date. Conversely, those present in the psyllium stem are very similar to those in other eudicots. This suggests these genes are under selective pressure, likely due to the synthesis of the various xylan structures present in mucilage that has a different biochemical role than that present in secondary walls. The numerous GT61 family members also show a wide sequence diversity and may be responsible for the larger number of side chain structures present in the psyllium mucilage.

No MeSH data available.