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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.


Phylogenetic analysis of glycosyltransferase family 61 proteins from psyllium, Arabidopsis, rice and Brachypodium distachyon. Seven cDNAs displaying homology to At3g18170 and At3g18180 were cloned from psyllium mucilaginous layers and their full-length protein sequences deduced. A few transcripts encoding protein sequences homologous to some of the other six GT61 proteins in Arabidopsis were identified in the mucilagionous layers but these were expressed at negligible levels (<10 pm) and were not included in this analysis. The seven GT61 proteins highly expressed in psyllium mucilaginous layers (light blue) were aligned with all glycosyltransferase family 61 proteins from Arabidopsis (dark blue), rice (red) and Brachypodium distachyon (pink).
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Figure 5: Phylogenetic analysis of glycosyltransferase family 61 proteins from psyllium, Arabidopsis, rice and Brachypodium distachyon. Seven cDNAs displaying homology to At3g18170 and At3g18180 were cloned from psyllium mucilaginous layers and their full-length protein sequences deduced. A few transcripts encoding protein sequences homologous to some of the other six GT61 proteins in Arabidopsis were identified in the mucilagionous layers but these were expressed at negligible levels (<10 pm) and were not included in this analysis. The seven GT61 proteins highly expressed in psyllium mucilaginous layers (light blue) were aligned with all glycosyltransferase family 61 proteins from Arabidopsis (dark blue), rice (red) and Brachypodium distachyon (pink).

Mentions: Figure 5 presents a phylogenetic tree of PoGT61_1 to _7 and all GT61 proteins identified in Arabidopsis, rice and B. distachyon (ClustalW alignment in File S4). The phylogenetic tree shows that the large diversification in grasses of this family is unrelated to the diversification found in psyllium. Therefore, the similar modifications of the xylan backbone found in psyllium ML and grasses are likely the results of convergent evolution.


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)

Phylogenetic analysis of glycosyltransferase family 61 proteins from psyllium, Arabidopsis, rice and Brachypodium distachyon. Seven cDNAs displaying homology to At3g18170 and At3g18180 were cloned from psyllium mucilaginous layers and their full-length protein sequences deduced. A few transcripts encoding protein sequences homologous to some of the other six GT61 proteins in Arabidopsis were identified in the mucilagionous layers but these were expressed at negligible levels (<10 pm) and were not included in this analysis. The seven GT61 proteins highly expressed in psyllium mucilaginous layers (light blue) were aligned with all glycosyltransferase family 61 proteins from Arabidopsis (dark blue), rice (red) and Brachypodium distachyon (pink).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Phylogenetic analysis of glycosyltransferase family 61 proteins from psyllium, Arabidopsis, rice and Brachypodium distachyon. Seven cDNAs displaying homology to At3g18170 and At3g18180 were cloned from psyllium mucilaginous layers and their full-length protein sequences deduced. A few transcripts encoding protein sequences homologous to some of the other six GT61 proteins in Arabidopsis were identified in the mucilagionous layers but these were expressed at negligible levels (<10 pm) and were not included in this analysis. The seven GT61 proteins highly expressed in psyllium mucilaginous layers (light blue) were aligned with all glycosyltransferase family 61 proteins from Arabidopsis (dark blue), rice (red) and Brachypodium distachyon (pink).
Mentions: Figure 5 presents a phylogenetic tree of PoGT61_1 to _7 and all GT61 proteins identified in Arabidopsis, rice and B. distachyon (ClustalW alignment in File S4). The phylogenetic tree shows that the large diversification in grasses of this family is unrelated to the diversification found in psyllium. Therefore, the similar modifications of the xylan backbone found in psyllium ML and grasses are likely the results of convergent evolution.

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.