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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.


Acetylation levels in alcohol insoluble residue of psyllium seed tissues.
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Figure 6: Acetylation levels in alcohol insoluble residue of psyllium seed tissues.

Mentions: The top member is homologous to Arabidopsis TBR38 and contains a domain of unknown function (DUF) 231. The DUF231 proteins constitute a 46-member protein family in Arabidopsis (Bischoff et al., 2010) in which the genes AXY4 (TBL27) and AXY4-Like (TBL22) have been shown to be involved in acetylation of xyloglucan (Gille et al., 2011) and ESK1 (TBL29) have been shown to be involved in acetylation of secondary cell wall xylan (Xiong et al., 2013). The other members of this family have been proposed to also be acetyltransferases specific for xyloglucan or other cell wall polymers, e.g., pectins and xylan (Oikawa et al., 2010; Gille and Pauly, 2012). TBR38 is part of an uncharacterized subclade of the TBR protein family. Given that the psyllium homolog has a much higher expression in the ML than the secondary cell wall CESA proteins it is likely involved in complex heteroxylan biosynthesis rather than secondary cell wall formation in this tissue. The level of cell wall acetylation in dissected psyllium ML is 12 μg acetic acid per milligram alcohol insoluble residue, approximately 4 fold lower that found in the alcohol insoluble residue of Arabidopsis lower stem (Figure 6). The acetic acid content in the psyllium ML corresponds to one acetic acid group for every 25 pentose sugars, assuming the cell wall material from the ML consist of 100% pentose sugars. Glucuronoxylan from aspen wood has been found to have an average degree of xylose backbone acetylation of approximately 60% (Teleman et al., 2000), while a degree of acetylation of approximately 50% has been found for arabinoxylan from corncobs and corn stover (Dongen et al., 2011). These findings may indicate that TBR38 and its psyllium homolog could function as xylan specific acetyltransferases.


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)

Acetylation levels in alcohol insoluble residue of psyllium seed tissues.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Acetylation levels in alcohol insoluble residue of psyllium seed tissues.
Mentions: The top member is homologous to Arabidopsis TBR38 and contains a domain of unknown function (DUF) 231. The DUF231 proteins constitute a 46-member protein family in Arabidopsis (Bischoff et al., 2010) in which the genes AXY4 (TBL27) and AXY4-Like (TBL22) have been shown to be involved in acetylation of xyloglucan (Gille et al., 2011) and ESK1 (TBL29) have been shown to be involved in acetylation of secondary cell wall xylan (Xiong et al., 2013). The other members of this family have been proposed to also be acetyltransferases specific for xyloglucan or other cell wall polymers, e.g., pectins and xylan (Oikawa et al., 2010; Gille and Pauly, 2012). TBR38 is part of an uncharacterized subclade of the TBR protein family. Given that the psyllium homolog has a much higher expression in the ML than the secondary cell wall CESA proteins it is likely involved in complex heteroxylan biosynthesis rather than secondary cell wall formation in this tissue. The level of cell wall acetylation in dissected psyllium ML is 12 μg acetic acid per milligram alcohol insoluble residue, approximately 4 fold lower that found in the alcohol insoluble residue of Arabidopsis lower stem (Figure 6). The acetic acid content in the psyllium ML corresponds to one acetic acid group for every 25 pentose sugars, assuming the cell wall material from the ML consist of 100% pentose sugars. Glucuronoxylan from aspen wood has been found to have an average degree of xylose backbone acetylation of approximately 60% (Teleman et al., 2000), while a degree of acetylation of approximately 50% has been found for arabinoxylan from corncobs and corn stover (Dongen et al., 2011). These findings may indicate that TBR38 and its psyllium homolog could function as xylan specific acetyltransferases.

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.