Rowan Mitchell - Academia.edu (original) (raw)

Papers by Rowan Mitchell

Research paper thumbnail of Modification of plant cell walls with hydroxycinnamic acids by BAHD acyltransferases

Frontiers in Plant Science

In the last decade it has become clear that enzymes in the “BAHD” family of acyl-CoA transferases... more In the last decade it has become clear that enzymes in the “BAHD” family of acyl-CoA transferases play important roles in the addition of phenolic acids to form ester-linked moieties on cell wall polymers. We focus here on the addition of two such phenolics—the hydroxycinnamates, ferulate and p-coumarate—to two cell wall polymers, glucuronoarabinoxylan and to lignin. The resulting ester-linked feruloyl and p-coumaroyl moities are key features of the cell walls of grasses and other commelinid monocots. The capacity of ferulate to participate in radical oxidative coupling means that its addition to glucuronoarabinoxylan or to lignin has profound implications for the properties of the cell wall – allowing respectively oxidative crosslinking to glucuronoarabinoxylan chains or introducing ester bonds into lignin polymers. A subclade of ~10 BAHD genes in grasses is now known to (1) contain genes strongly implicated in addition of p-coumarate or ferulate to glucuronoarabinoxylan (2) encode...

Research paper thumbnail of Elucidation of the Structure and Biosynthesis of Wheat Grain Mannan

International audienceCereal grain cell walls are studied for their nutritional benefits (dietary... more International audienceCereal grain cell walls are studied for their nutritional benefits (dietary fibre), their adverse effects on the digestive health of livestock such as poultry and pigs, and their effects on grain usage (bread making, pasta, brewing...). In wheat grain, the two major cell wall polysaccharides, arabinoxylans and β-glucans, have been extensively studied. By contrast, mannan was poorly documented. Nevertheless, this hemicellulosic polysaccharide might have a determinant role in wheat grain development since, in Arabidopsis thaliana, mutants with a reduced amount of mannan show an altered seed development. Our project aimed at deciphering the biochemical structure and the biological function of mannan. To study the biological function of mannan, we have studied its occurrence during wheat grain development. The detection of mannan using monoclonal antibodies showed that mannan is mainly located in the grain endosperm and that its deposition starts at an intermediate...

Research paper thumbnail of Additional file 5 of High post-anthesis temperature effects on bread wheat (Triticum aestivum L.) grain transcriptome during early grain-filling

Additional File 5. Diagram of experimental design.

Research paper thumbnail of Report on the identification of ploidy of accessions to identify appropriate parents for breeding at diploid and polyploid levels across the germplasm collection for Brachiaria

Research paper thumbnail of Limonium gibertii partial mRNA for ribulose 1,5 bisphosphate carboxylase/oxygenase small subunit (rbcS1 gene)

Research paper thumbnail of Yield experiments allow scientists to read the tea-leaves

Research paper thumbnail of Climate change: plant production and photosynthetic regulation by environment

Research paper thumbnail of Exploiting genetic variation to increase the dietary fibre content of wheat grain and flour

Research paper thumbnail of Limonium gibertii mRNA for ribulose 1,5 bisphosphate carboxylase/oxygenase large subunit (rbcL gene)

Research paper thumbnail of The effects of increased temperature and CO2 concentration on winter wheat: test of model predictions

Research paper thumbnail of RNAi suppression of xylan synthase genes in wheat starchy endosperm

PLoS ONE, 2021

The xylan backbone of arabinoxylan (AX), the major cell wall polysaccharide in the wheat starchy ... more The xylan backbone of arabinoxylan (AX), the major cell wall polysaccharide in the wheat starchy endosperm, is synthesised by xylan synthase which is a complex of three subunits encoded by the GT43_1, GT43_2 and GT47_2 genes. RNAi knock-down of either GT43_1 or all three genes (triple lines) resulted in decreased AX measured by digestion with endoxylanase (to 33 and 34.9% of the controls) and by monosaccharide analysis (to 45.9% and 47.4% of the controls) with greater effects on the amount of water-extractable AX (to 20.6 and 19.9% of the controls). Both sets of RNAi lines also had greater decreases in the amounts of substituted oligosaccharides released by digestion of AX with endoxylanase than in fragments derived only from the xylan backbone. Although the GT43_1 and triple lines had similar effects on AX they did differ in their contents of soluble sugars (increased in triple only) and on grain size (decreased in triple only). Both sets of transgenic lines had decreased grain har...

Research paper thumbnail of Climate change and winter wheat: effects on photosynthesis, productivity and yield

Research paper thumbnail of Flow cytometry-based determination of ploidy from dried leaf specimens in genomically complex collections of the tropical forage grass Urochloa s. l

We aimed to develop an optimized approach to determine ploidy for dried leaf material in a germpl... more We aimed to develop an optimized approach to determine ploidy for dried leaf material in a germplasm collection of a tropical forage grass group, including approaches to collect, dry and preserve plant samples for flow cytometry analysis. Urochloa (including Brachiaria, Megathyrus and some Panicum) tropical grasses are native to Africa and are now, after selection and breeding, planted worldwide, particularly in South America, as important forages with huge potential for further sustainable improvement and conservation of grasslands. The methods enable robust identification of ploidy levels (coefficient of variation, CV, typically <5%). Ploidy of some 353 forage grass accessions (ploidy range from 2 to 9), from international genetic resource collections, showing variation in basic chromosome numbers and reproduction modes (apomixis and sexual), were determined using our defined standard protocol. Two major Urochloa agamic complexes used in the current breeding programs at CIAT an...

Research paper thumbnail of Allele Mining in Diverse Accessions of Urochloa and Megathyrsus spp. Tropical Grasses to Improve Forage Quality and Reduce Environmental Impact

The C4 Urochloa spp (syn. Brachiaria) and Megathyrsus maximus (syn. Panicum maximum) are used as ... more The C4 Urochloa spp (syn. Brachiaria) and Megathyrsus maximus (syn. Panicum maximum) are used as pasture for cattle across vast areas in tropical agriculture systems in Africa and South America. A key target for variety improvement is forage quality: enhanced digestibility could decrease amount of land required per unit production and enhanced lipid content could decrease methane emissions from cattle. For these traits, loss-of-function (LOF) alleles in known gene targets are predicted to improve them, making a reverse genetics approach of allele mining feasible. We studied allelic diversity of 20 target genes (11 for digestibility, 9 for lipid content) in 104 accessions selected to represent genetic diversity and ploidy levels of U. brizantha, U. decumbens, U. humidicola, U. ruziziensis and M. maximum. We used RNAseq and then bait-capture DNA-seq to improve gene models in a U. ruziziensis reference genome to assign polymorphisms with high confidence. We found 953 non-synonymous pol...

Research paper thumbnail of Identification of a major QTL and associated molecular marker for high arabinoxylan fibre in white wheat flour

Research paper thumbnail of High post-anthesis temperature effects on bread wheat (Triticum aestivum L.) grain transcriptome during early grain-filling

Background: High post-anthesis (p.a) temperatures reduce mature grain weight in wheat. However, t... more Background: High post-anthesis (p.a) temperatures reduce mature grain weight in wheat. However, the causes of this reduction are not entirely known. Control of grain expansion by the maternally derived pericarp of the grain has previously been suggested, although this interaction has not been investigated under high p.a. temperatures. Down-regulation of pericarp localised genes that regulate cell wall expansion under high p.a. temperatures may limit expansion of the encapsulated endosperm due to a loss of plasticity in the pericarp, reducing mature grain weight. Here the effect of high p.a. temperatures on the transcriptome of the pericarp and endosperm of the wheat grain during early grain-filling was investigated via RNA-Seq and is discussed alongside grain moisture dynamics during early grain development and mature grain weight. Results: High p.a. temperatures applied from 6-days after anthesis (daa) and until 18daa reduced the grain’s ability to accumulate water, with total grai...

Research paper thumbnail of Crop ecosystem responses to climatic change: wheat

Climate change and global crop productivity., 2000

This chapter considers the likely responses of wheat to the primary factors associated with globa... more This chapter considers the likely responses of wheat to the primary factors associated with global environmental change, increasing atmospheric carbon dioxide concentration, increasing environmental temperature and predicted global warming.

Research paper thumbnail of Photosynthetic Acclimation of Winter Wheat to Elevated CO2 and Temperature

Photosynthesis: from Light to Biosphere, 1995

Research paper thumbnail of Dietary Fibre: Wheat Genes for Enhanced Human Health

Advances in Wheat Genetics: From Genome to Field, 2015

Research paper thumbnail of Glycosyl transferases in family 61 mediate arabinofuranosyl transfer onto xylan in grasses

Proceedings of the National Academy of Sciences, 2012

Xylan, a hemicellulosic component of the plant cell wall, is one of the most abundant polysacchar... more Xylan, a hemicellulosic component of the plant cell wall, is one of the most abundant polysaccharides in nature. In contrast to dicots, xylan in grasses is extensively modified by α-(1,2)– and α-(1,3)–linked arabinofuranose. Despite the importance of grass arabinoxylan in human and animal nutrition and for bioenergy, the enzymes adding the arabinosyl substitutions are unknown. Here we demonstrate that knocking-down glycosyltransferase (GT) 61 expression in wheat endosperm strongly decreases α-(1,3)–linked arabinosyl substitution of xylan. Moreover, heterologous expression of wheat and rice GT61s in Arabidopsis leads to arabinosylation of the xylan, and therefore provides gain-of-function evidence for α-(1,3)-arabinosyltransferase activity. Thus, GT61 proteins play a key role in arabinoxylan biosynthesis and therefore in the evolutionary divergence of grass cell walls.

Research paper thumbnail of Modification of plant cell walls with hydroxycinnamic acids by BAHD acyltransferases

Frontiers in Plant Science

In the last decade it has become clear that enzymes in the “BAHD” family of acyl-CoA transferases... more In the last decade it has become clear that enzymes in the “BAHD” family of acyl-CoA transferases play important roles in the addition of phenolic acids to form ester-linked moieties on cell wall polymers. We focus here on the addition of two such phenolics—the hydroxycinnamates, ferulate and p-coumarate—to two cell wall polymers, glucuronoarabinoxylan and to lignin. The resulting ester-linked feruloyl and p-coumaroyl moities are key features of the cell walls of grasses and other commelinid monocots. The capacity of ferulate to participate in radical oxidative coupling means that its addition to glucuronoarabinoxylan or to lignin has profound implications for the properties of the cell wall – allowing respectively oxidative crosslinking to glucuronoarabinoxylan chains or introducing ester bonds into lignin polymers. A subclade of ~10 BAHD genes in grasses is now known to (1) contain genes strongly implicated in addition of p-coumarate or ferulate to glucuronoarabinoxylan (2) encode...

Research paper thumbnail of Elucidation of the Structure and Biosynthesis of Wheat Grain Mannan

International audienceCereal grain cell walls are studied for their nutritional benefits (dietary... more International audienceCereal grain cell walls are studied for their nutritional benefits (dietary fibre), their adverse effects on the digestive health of livestock such as poultry and pigs, and their effects on grain usage (bread making, pasta, brewing...). In wheat grain, the two major cell wall polysaccharides, arabinoxylans and β-glucans, have been extensively studied. By contrast, mannan was poorly documented. Nevertheless, this hemicellulosic polysaccharide might have a determinant role in wheat grain development since, in Arabidopsis thaliana, mutants with a reduced amount of mannan show an altered seed development. Our project aimed at deciphering the biochemical structure and the biological function of mannan. To study the biological function of mannan, we have studied its occurrence during wheat grain development. The detection of mannan using monoclonal antibodies showed that mannan is mainly located in the grain endosperm and that its deposition starts at an intermediate...

Research paper thumbnail of Additional file 5 of High post-anthesis temperature effects on bread wheat (Triticum aestivum L.) grain transcriptome during early grain-filling

Additional File 5. Diagram of experimental design.

Research paper thumbnail of Report on the identification of ploidy of accessions to identify appropriate parents for breeding at diploid and polyploid levels across the germplasm collection for Brachiaria

Research paper thumbnail of Limonium gibertii partial mRNA for ribulose 1,5 bisphosphate carboxylase/oxygenase small subunit (rbcS1 gene)

Research paper thumbnail of Yield experiments allow scientists to read the tea-leaves

Research paper thumbnail of Climate change: plant production and photosynthetic regulation by environment

Research paper thumbnail of Exploiting genetic variation to increase the dietary fibre content of wheat grain and flour

Research paper thumbnail of Limonium gibertii mRNA for ribulose 1,5 bisphosphate carboxylase/oxygenase large subunit (rbcL gene)

Research paper thumbnail of The effects of increased temperature and CO2 concentration on winter wheat: test of model predictions

Research paper thumbnail of RNAi suppression of xylan synthase genes in wheat starchy endosperm

PLoS ONE, 2021

The xylan backbone of arabinoxylan (AX), the major cell wall polysaccharide in the wheat starchy ... more The xylan backbone of arabinoxylan (AX), the major cell wall polysaccharide in the wheat starchy endosperm, is synthesised by xylan synthase which is a complex of three subunits encoded by the GT43_1, GT43_2 and GT47_2 genes. RNAi knock-down of either GT43_1 or all three genes (triple lines) resulted in decreased AX measured by digestion with endoxylanase (to 33 and 34.9% of the controls) and by monosaccharide analysis (to 45.9% and 47.4% of the controls) with greater effects on the amount of water-extractable AX (to 20.6 and 19.9% of the controls). Both sets of RNAi lines also had greater decreases in the amounts of substituted oligosaccharides released by digestion of AX with endoxylanase than in fragments derived only from the xylan backbone. Although the GT43_1 and triple lines had similar effects on AX they did differ in their contents of soluble sugars (increased in triple only) and on grain size (decreased in triple only). Both sets of transgenic lines had decreased grain har...

Research paper thumbnail of Climate change and winter wheat: effects on photosynthesis, productivity and yield

Research paper thumbnail of Flow cytometry-based determination of ploidy from dried leaf specimens in genomically complex collections of the tropical forage grass Urochloa s. l

We aimed to develop an optimized approach to determine ploidy for dried leaf material in a germpl... more We aimed to develop an optimized approach to determine ploidy for dried leaf material in a germplasm collection of a tropical forage grass group, including approaches to collect, dry and preserve plant samples for flow cytometry analysis. Urochloa (including Brachiaria, Megathyrus and some Panicum) tropical grasses are native to Africa and are now, after selection and breeding, planted worldwide, particularly in South America, as important forages with huge potential for further sustainable improvement and conservation of grasslands. The methods enable robust identification of ploidy levels (coefficient of variation, CV, typically <5%). Ploidy of some 353 forage grass accessions (ploidy range from 2 to 9), from international genetic resource collections, showing variation in basic chromosome numbers and reproduction modes (apomixis and sexual), were determined using our defined standard protocol. Two major Urochloa agamic complexes used in the current breeding programs at CIAT an...

Research paper thumbnail of Allele Mining in Diverse Accessions of Urochloa and Megathyrsus spp. Tropical Grasses to Improve Forage Quality and Reduce Environmental Impact

The C4 Urochloa spp (syn. Brachiaria) and Megathyrsus maximus (syn. Panicum maximum) are used as ... more The C4 Urochloa spp (syn. Brachiaria) and Megathyrsus maximus (syn. Panicum maximum) are used as pasture for cattle across vast areas in tropical agriculture systems in Africa and South America. A key target for variety improvement is forage quality: enhanced digestibility could decrease amount of land required per unit production and enhanced lipid content could decrease methane emissions from cattle. For these traits, loss-of-function (LOF) alleles in known gene targets are predicted to improve them, making a reverse genetics approach of allele mining feasible. We studied allelic diversity of 20 target genes (11 for digestibility, 9 for lipid content) in 104 accessions selected to represent genetic diversity and ploidy levels of U. brizantha, U. decumbens, U. humidicola, U. ruziziensis and M. maximum. We used RNAseq and then bait-capture DNA-seq to improve gene models in a U. ruziziensis reference genome to assign polymorphisms with high confidence. We found 953 non-synonymous pol...

Research paper thumbnail of Identification of a major QTL and associated molecular marker for high arabinoxylan fibre in white wheat flour

Research paper thumbnail of High post-anthesis temperature effects on bread wheat (Triticum aestivum L.) grain transcriptome during early grain-filling

Background: High post-anthesis (p.a) temperatures reduce mature grain weight in wheat. However, t... more Background: High post-anthesis (p.a) temperatures reduce mature grain weight in wheat. However, the causes of this reduction are not entirely known. Control of grain expansion by the maternally derived pericarp of the grain has previously been suggested, although this interaction has not been investigated under high p.a. temperatures. Down-regulation of pericarp localised genes that regulate cell wall expansion under high p.a. temperatures may limit expansion of the encapsulated endosperm due to a loss of plasticity in the pericarp, reducing mature grain weight. Here the effect of high p.a. temperatures on the transcriptome of the pericarp and endosperm of the wheat grain during early grain-filling was investigated via RNA-Seq and is discussed alongside grain moisture dynamics during early grain development and mature grain weight. Results: High p.a. temperatures applied from 6-days after anthesis (daa) and until 18daa reduced the grain’s ability to accumulate water, with total grai...

Research paper thumbnail of Crop ecosystem responses to climatic change: wheat

Climate change and global crop productivity., 2000

This chapter considers the likely responses of wheat to the primary factors associated with globa... more This chapter considers the likely responses of wheat to the primary factors associated with global environmental change, increasing atmospheric carbon dioxide concentration, increasing environmental temperature and predicted global warming.

Research paper thumbnail of Photosynthetic Acclimation of Winter Wheat to Elevated CO2 and Temperature

Photosynthesis: from Light to Biosphere, 1995

Research paper thumbnail of Dietary Fibre: Wheat Genes for Enhanced Human Health

Advances in Wheat Genetics: From Genome to Field, 2015

Research paper thumbnail of Glycosyl transferases in family 61 mediate arabinofuranosyl transfer onto xylan in grasses

Proceedings of the National Academy of Sciences, 2012

Xylan, a hemicellulosic component of the plant cell wall, is one of the most abundant polysacchar... more Xylan, a hemicellulosic component of the plant cell wall, is one of the most abundant polysaccharides in nature. In contrast to dicots, xylan in grasses is extensively modified by α-(1,2)– and α-(1,3)–linked arabinofuranose. Despite the importance of grass arabinoxylan in human and animal nutrition and for bioenergy, the enzymes adding the arabinosyl substitutions are unknown. Here we demonstrate that knocking-down glycosyltransferase (GT) 61 expression in wheat endosperm strongly decreases α-(1,3)–linked arabinosyl substitution of xylan. Moreover, heterologous expression of wheat and rice GT61s in Arabidopsis leads to arabinosylation of the xylan, and therefore provides gain-of-function evidence for α-(1,3)-arabinosyltransferase activity. Thus, GT61 proteins play a key role in arabinoxylan biosynthesis and therefore in the evolutionary divergence of grass cell walls.