Ros Gleadow | Monash University (original) (raw)

Papers by Ros Gleadow

Many important food crops produce cyanogenic glucosides as natural defense compounds to protect a... more Many important food crops produce cyanogenic glucosides as natural defense compounds to protect against herbivory or pathogen attack. It has also been suggested that these nitrogen-based secondary metabolites act as storage reserves of nitrogen. In sorghum, three key genes, CYP79A1, CYP71E1 and UGT85B1, encode two Cytochrome P450s and a glycosyltransferase, respectively, the enzymes essential for synthesis of the cyanogenic glucoside dhurrin. Here, we report the use of targeted induced local lesions in genomes (TILLING) to identify a line with a mutation resulting in a premature stop codon in the N-terminal region of UGT85B1. Plants homozygous for this mutation do not produce dhurrin and are designated tcd2 (totally cyanide deficient2) mutants. They have reduced vigor, being dwarfed, with poor root development and low fertility. Analysis using liquid chromatography–mass spectrometry (LC-MS) shows that tcd2 mutants accumulate numerous dhurrin pathway derived metabolites, some of which are similar to those observed in transgenic Arabidopsis expressing the CYP79A1 and CYP71E1 genes. Our results demonstrate
that UGT85B1 is essential for formation of dhurrin in sorghum with no co-expressed endogenous UDP-glucosyltransferases able to replace it. The tcd2 mutant suffers from self-intoxication because sorghum does not have a feedback mechanism to inhibit the initial steps of dhurrin biosynthesis when the glucosyltransferase activity required to complete the synthesis of dhurrin is lacking. The LC-MS analyses also revealed the presence of metabolites in the tcd2 mutant which have been suggested to be derived from dhurrin via endogenous pathways for nitrogen recovery, thus indicating which enzymes may be involved in such pathways.

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Cassava (Manihot esculenta) provides calories and nutrition for more than half a billion people. ... more Cassava (Manihot esculenta) provides calories and nutrition for more than half a billion people. It was domesticated by native
Amazonian peoples through cultivation of the wild progenitor M. esculenta ssp. flabellifolia and is now grown in tropical regions
worldwide. Here we provide a high-quality genome assembly for cassava with improved contiguity, linkage, and completeness;
almost 97% of genes are anchored to chromosomes. We find that paleotetraploidy in cassava is shared with the related rubber
tree Hevea, providing a resource for comparative studies. We also sequence a global collection of 58 Manihot accessions,
including cultivated and wild cassava accessions and related species such as Ceará or India rubber (M. glaziovii), and genotype
268 African cassava varieties. We find widespread interspecific admixture, and detect the genetic signature of past cassava
breeding programs. As a clonally propagated crop, cassava is especially vulnerable to pathogens and abiotic stresses.
This genomic resource will inform future genome-enabled breeding efforts to improve this staple crop

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Global Change Biology, 2016

Cassava is an important dietary component for over 1 billion people, and its ability to yield und... more Cassava is an important dietary component for over 1 billion people, and its ability to yield under drought has led to it being promoted as an important crop for food security under climate change. Despite its known photosynthetic plasticity in response to temperature, little is known about how temperature affects plant toxicity or about interactions between temperature and drought, which is important because cassava tissues contain high levels of toxic cyanogenic glucosides, a major health and food safety concern. In a controlled glasshouse experiment, plants were grown at 2 daytime temperatures (23 °C and 34 °C), and either well-watered or subject to a 1 month drought prior to harvest at 6 months. The objective was to determine the separate and interactive effects of temperature and drought on growth and toxicity. Both temperature and drought affected cassava physiology and chemistry. While temperature alone drove differences in plant height and above-ground biomass, drought and temperature × drought interactions most affected tuber yield, as well as foliar and tuber chemistry, including C : N, nitrogen and cyanide potential (CNp; total cyanide released from cyanogenic glucosides). Conditions that most stimulated growth and yield (well-watered × high temperature) effected a reduction in tuber toxicity, whereas drought inhibited growth and yield, and was associated with increased foliar and tuber toxicity. The magnitude of drought effects on tuber yield and toxicity were greater at high temperature; thus, increases in tuber CNp were not merely a consequence of reduced tuber biomass. Findings confirm that cassava is adaptable to forecast temperature increases, particularly in areas of adequate or increasing rainfall; however, in regions forecast for increased incidence of drought, the effects of drought on both food quality (tuber toxicity) and yield are a greater threat to future food security and indicate an increasing necessity for processing of cassava to reduce toxicity.

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Journal of Experimental Botany, 2016

Rising sea levels are threatening agricultural production in coastal regions due to inundation an... more Rising sea levels are threatening agricultural production in coastal regions due to inundation and contamination of groundwater. The development of more salt-tolerant crops is essential. Cassava is an important staple, particularly among poor subsistence farmers. Its tolerance to drought and elevated temperatures make it highly suitable for meeting global food demands in the face of climate change, but its ability to tolerate salt is unknown. Cassava stores nitrogen in the form of cyanogenic glucosides and can cause cyanide poisoning unless correctly processed. Previous research demonstrated that cyanide levels are higher in droughted plants, possibly as a mechanism for increasing resilience to oxidative stress. We determined the tolerance of cassava to salt at two different stages of development, and tested the hypothesis that cyanide toxicity would be higher in salt-stressed plants. Cassava was grown at a range of concentrations of sodium chloride (NaCl) at two growth stages: tuber initiation and tuber expansion. Established plants were able to tolerate 100mM NaCl but in younger plants 40mM was sufficient to retard plant growth severely. Nutrient analysis showed that plants were only able to exclude sodium at low concentrations. The foliar cyanogenic glucoside concentration in young plants increased under moderate salinity stress but was lower in plants grown at high salt. Importantly, there was no significant change in the cyanogenic glucoside concentration in the tubers. We propose that the mechanisms for salinity tolerance are age dependent, and that this can be traced to the relative cost of leaves in young and old plants.

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Plants have evolved a vast array of defence mechanisms to avoid or minimize damage caused by herb... more Plants have evolved a vast array of defence mechanisms to avoid or minimize damage caused by herbi-vores and pathogens. The costs and benefits of defences are thought to vary with the availability of resources, herbivore pressure and plant functional traits. We investigated the resource (nitrogen) and growth cost of deploying cyanogenic glycosides in seedlings of Eucalyptus cladocalyx (Myrta-ceae). To do this, we grew the plants under a range of soil N conditions, from levels that were limiting for growth to those that were saturating for growth, and we measured correlations between foliar chemical and performance attributes. Within each N treatment, we found evidence that, for every N invested in cyanogenic glycosides, additional N is added to the leaf. For the lowest N treatment, the additional N was less than one per cyanogenic glycoside, rising to some two Ns for the other treatments. The interaction between cyanogenic glycosides and both condensed tannins and total phenolic compounds was also examined, but we did not detect correlations between these compounds under constant leaf N concentrations. Finally, we did not detect a correlation between net assimilation rate, relative growth rate and cyanogenic glycoside concentrations under any soil N treatment. We conclude that the growth cost of cyanogenic glycosides was likely too low to detect and that it was offset to some degree by additional N that was allocated alongside the cyanogenic glycosides.

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Cassava (Manihot esculenta) provides calories and nutrition for more than half a billion people. ... more Cassava (Manihot esculenta) provides calories and nutrition for more than half a billion people. It was domesticated by native Amazonian peoples through cultivation of the wild progenitor M. esculenta ssp. flabellifolia and is now grown in tropical regions worldwide. Here we provide a high-quality genome assembly for cassava with improved contiguity, linkage, and completeness; almost 97% of genes are anchored to chromosomes. We find that paleotetraploidy in cassava is shared with the related rubber tree Hevea, providing a resource for comparative studies. We also sequence a global collection of 58 Manihot accessions, including cultivated and wild cassava accessions and related species such as Ceará or India rubber (M. glaziovii), and genotype 268 African cassava varieties. We find widespread interspecific admixture, and detect the genetic signature of past cassava breeding programs. As a clonally propagated crop, cassava is especially vulnerable to pathogens and abiotic stresses.
This genomic resource will inform future genome-enabled breeding efforts to improve this staple crop.

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Abstract The importance of algae-derived biofuels has been highlighted by the current problems as... more Abstract The importance of algae-derived biofuels has been
highlighted by the current problems associated with fossil
fuels. Considerable past research has shown that limiting nutrients
such as nitrogen and phosphorus increases the cellular
lipid content in microalgae. However, limiting the supply of
nutrients results in decreased biomass, which in turn decreases
the overall lipid productivity of cultures. Therefore, nutrient
limitation has been a subject of dispute as to whether it will
benefit biofuel production on an industrial scale. Our research
explores the physiological changes a cell undergoes when
exposed to nitrogen and phosphorus limitations, both individually
and in combination, and also examines the biotechnological
aspects of manipulating N and P in order to increase
cellular lipids, by analyzing the lipid production. We show
that nitrogen starvation and also nitrogen plus phosphorus
starvation combined have a more profound effect on the physiology
and macromolecular pools of Chlamydomonas
reinhardtii than does phosphorus starvation alone. The photosynthetic
performance of C. reinhardtii underwent drastic
changes under nitrogen starvation, but remained relatively unaffected
under phosphorus starvation. The neutral lipid concentration
per cell was at least 2.4-fold higher in all the
nutrient-starved groups than the nutrient-replete controls, but
the protein level per cell was lower in the nitrogen-starved
groups. Overall, nitrogen starvation has a more dramatic effect
on the physiology and neutral lipids and protein levels of
C. reinhardtii than phosphorus starvation. However, the level
of total lipids per volume of culture obtained was similar
among nutrient-replete and all of the nutrient-starved groups.
We conclude that combined nitrogen and phosphorus starvation
does not likely benefit biofuel production in terms of
enhanced lipid or biomass production

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Many important food crops produce cyanogenic glucosides as natural defense compounds to protect a... more Many important food crops produce cyanogenic glucosides
as natural defense compounds to protect against herbivory
or pathogen attack. It has also been suggested that these
nitrogen-based secondary metabolites act as storage
reserves of nitrogen. In sorghum, three key genes,
CYP79A1, CYP71E1 and UGT85B1, encode two Cytochrome
P450s and a glycosyltransferase, respectively, the enzymes
essential for synthesis of the cyanogenic glucoside dhurrin.
Here, we report the use of targeted induced local lesions in
genomes (TILLING) to identify a line with a mutation resulting
in a premature stop codon in the N-terminal region of
UGT85B1. Plants homozygous for this mutation do not produce
dhurrin and are designated tcd2 (totally cyanide deficient
2) mutants. They have reduced vigor, being dwarfed,
with poor root development and low fertility. Analysis using
liquid chromatography–mass spectrometry (LC-MS) shows
that tcd2 mutants accumulate numerous dhurrin pathwayderived
metabolites, some of which are similar to those
observed in transgenic Arabidopsis expressing the
CYP79A1 and CYP71E1 genes. Our results demonstrate
that UGT85B1 is essential for formation of dhurrin in sorghum
with no co-expressed endogenous UDP-glucosyltransferases
able to replace it. The tcd2 mutant suffers from
self-intoxication because sorghum does not have a feedback
mechanism to inhibit the initial steps of dhurrin biosynthesis
when the glucosyltransferase activity required to complete
the synthesis of dhurrin is lacking. The LC-MS analyses
also revealed the presence of metabolites in the tcd2 mutant
which have been suggested to be derived from dhurrin via
endogenous pathways for nitrogen recovery, thus indicating
which enzymes may be involved in such pathways.

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Cyanogenic glycosides (CNglcs) are bioactive plant products derived from amino acids. Structurall... more Cyanogenic glycosides (CNglcs) are bioactive plant products derived from amino acids. Structurally, these specialized plant compounds are characterized as α-hydroxynitriles (cyanohydrins) that are stabilized by glucosylation. In recent years, improved tools within analytical chemistry have greatly increased the number of known CNglcs by enabling the discovery of less abundant CNglcs formed by additional hydroxylation, glycosylation, and acylation reactions. Cyanogenesis—the release of toxic hydrogen cyanide from endogenous CNglcs—is an effective defense against generalist herbi-vores but less effective against fungal pathogens. In the course of evolution, CNglcs have acquired additional roles to improve plant plasticity, i.e., establishment , robustness, and viability in response to environmental challenges. CNglc concentration is usually higher in young plants, when nitrogen is in ready supply, or when growth is constrained by nonoptimal growth conditions. Efforts are under way to engineer CNglcs into some crops as a pest control measure, whereas in other crops efforts are directed toward their removal to improve food safety. Given that many food crops are cyanogenic, it is important to understand the molecular mechanisms regulating cyanogen-esis so that the impact of future environmental challenges can be anticipated.

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Cassava is an important dietary component for over 1 billion people, and its ability to yield und... more Cassava is an important dietary component for over 1 billion people, and its ability to yield under drought has led to it being promoted as an important crop for food security under climate change. Despite its known photosynthetic plasticity in response to temperature, little is known about how temperature affects plant toxicity or about interactions between temperature and drought, which is important because cassava tissues contain high levels of toxic cya-nogenic glucosides, a major health and food safety concern. In a controlled glasshouse experiment, plants were grown at 2 daytime temperatures (23 °C and 34 °C), and either well-watered or subject to a 1 month drought prior to harvest at 6 months. The objective was to determine the separate and interactive effects of temperature and drought on growth and toxicity. Both temperature and drought affected cassava physiology and chemistry. While temperature alone drove differences in plant height and above-ground biomass, drought and temperature 9 drought interactions most affected tuber yield, as well as foliar and tuber chemistry, including C : N, nitrogen and cyanide potential (CNp; total cyanide released from cyanogenic glucosides). Conditions that most stimulated growth and yield (well-watered 9 high temperature) effected a reduction in tuber toxicity, whereas drought inhibited growth and yield, and was associated with increased foliar and tuber toxicity. The magnitude of drought effects on tuber yield and toxicity were greater at high temperature; thus, increases in tuber CNp were not merely a consequence of reduced tuber bio-mass. Findings confirm that cassava is adaptable to forecast temperature increases, particularly in areas of adequate or increasing rainfall; however, in regions forecast for increased incidence of drought, the effects of drought on both food quality (tuber toxicity) and yield are a greater threat to future food security and indicate an increasing necessity for processing of cassava to reduce toxicity.

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Rising sea levels are threatening agricultural production in coastal regions due to inundation an... more Rising sea levels are threatening agricultural production in coastal regions due to inundation and contamination of groundwater. The development of more salt-tolerant crops is essential. Cassava is an important staple, particularly among poor subsistence farmers. Its tolerance to drought and elevated temperatures make it highly suitable for meeting global food demands in the face of climate change, but its ability to tolerate salt is unknown. Cassava stores nitrogen in the form of cyanogenic glucosides and can cause cyanide poisoning unless correctly processed. Previous research demonstrated that cyanide levels are higher in droughted plants, possibly as a mechanism for increasing resilience to oxidative stress. We determined the tolerance of cassava to salt at two different stages of development, and tested the hypothesis that cyanide toxicity would be higher in salt-stressed plants. Cassava was grown at a range of concentrations of sodium chloride (NaCl) at two growth stages: tuber initiation and tuber expansion. Established plants were able to tolerate 100 mM NaCl but in younger plants 40 mM was sufficient to retard plant growth severely. Nutrient analysis showed that plants were only able to exclude sodium at low concentrations. The foliar cyanogenic glucoside concentration in young plants increased under moderate salinity stress but was lower in plants grown at high salt. Importantly, there was no significant change in the cyanogenic glucoside concentration in the tubers. We propose that the mechanisms for salinity tolerance are age dependent, and that this can be traced to the relative cost of leaves in young and old plants.

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Australian journal of plant physiology

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Journal of experimental botany, Jan 19, 2015

The use of high-throughput phenotyping systems and non-destructive imaging is widely regarded as ... more The use of high-throughput phenotyping systems and non-destructive imaging is widely regarded as a key technology allowing scientists and breeders to develop crops with the ability to perform well under diverse environmental conditions. However, many of these phenotyping studies have been optimized using the model plant Arabidopsis thaliana. In this study, The Plant Accelerator(®) at The University of Adelaide, Australia, was used to investigate the growth and phenotypic response of the important cereal crop, Sorghum bicolor L. Moench and related hybrids to water-limited conditions and different levels of fertilizer. Imaging in different spectral ranges was used to monitor plant composition, chlorophyll, and moisture content. Phenotypic image analysis accurately measured plant biomass. The data set obtained enabled the responses of the different sorghum varieties to the experimental treatments to be differentiated and modelled. Plant architectural instead of architecture elements we...

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Global Change Biology, 2016

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Journal of Experimental Botany, 2016

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Cassava (Manihot esculenta) provides calories and nutrition for more than half a billion people. ... more Cassava (Manihot esculenta) provides calories and nutrition for more than half a billion people. It was domesticated by native Amazonian peoples through cultivation of the wild progenitor M. esculenta ssp. flabellifolia and is now grown in tropical regions worldwide. Here we provide a high-quality genome assembly for cassava with improved contiguity, linkage, and completeness; almost 97% of genes are anchored to chromosomes. We find that paleotetraploidy in cassava is shared with the related rubber tree Hevea, providing a resource for comparative studies. We also sequence a global collection of 58 Manihot accessions, including cultivated and wild cassava accessions and related species such as Ceará or India rubber (M. glaziovii), and genotype 268 African cassava varieties. We find widespread interspecific admixture, and detect the genetic signature of past cassava breeding programs. As a clonally propagated crop, cassava is especially vulnerable to pathogens and abiotic stresses.
This genomic resource will inform future genome-enabled breeding efforts to improve this staple crop.

Bookmarks Related papers MentionsView impact

Many important food crops produce cyanogenic glucosides as natural defense compounds to protect a... more Many important food crops produce cyanogenic glucosides
as natural defense compounds to protect against herbivory
or pathogen attack. It has also been suggested that these
nitrogen-based secondary metabolites act as storage
reserves of nitrogen. In sorghum, three key genes,
CYP79A1, CYP71E1 and UGT85B1, encode two Cytochrome
P450s and a glycosyltransferase, respectively, the enzymes
essential for synthesis of the cyanogenic glucoside dhurrin.
Here, we report the use of targeted induced local lesions in
genomes (TILLING) to identify a line with a mutation resulting
in a premature stop codon in the N-terminal region of
UGT85B1. Plants homozygous for this mutation do not produce
dhurrin and are designated tcd2 (totally cyanide deficient
2) mutants. They have reduced vigor, being dwarfed,
with poor root development and low fertility. Analysis using
liquid chromatography–mass spectrometry (LC-MS) shows
that tcd2 mutants accumulate numerous dhurrin pathwayderived
metabolites, some of which are similar to those
observed in transgenic Arabidopsis expressing the
CYP79A1 and CYP71E1 genes. Our results demonstrate
that UGT85B1 is essential for formation of dhurrin in sorghum
with no co-expressed endogenous UDP-glucosyltransferases
able to replace it. The tcd2 mutant suffers from
self-intoxication because sorghum does not have a feedback
mechanism to inhibit the initial steps of dhurrin biosynthesis
when the glucosyltransferase activity required to complete
the synthesis of dhurrin is lacking. The LC-MS analyses
also revealed the presence of metabolites in the tcd2 mutant
which have been suggested to be derived from dhurrin via
endogenous pathways for nitrogen recovery, thus indicating
which enzymes may be involved in such pathways.

Bookmarks Related papers MentionsView impact

Cassava is an important dietary component for over 1 billion people, and its ability to yield und... more Cassava is an important dietary component for over 1 billion people, and its ability to yield under drought has led to it being promoted as an important crop for food security under climate change. Despite its known photosynthetic plasticity in response to temperature, little is known about how temperature affects plant toxicity or about interactions between temperature and drought, which is important because cassava tissues contain high levels of toxic cya-nogenic glucosides, a major health and food safety concern. In a controlled glasshouse experiment, plants were grown at 2 daytime temperatures (23 °C and 34 °C), and either well-watered or subject to a 1 month drought prior to harvest at 6 months. The objective was to determine the separate and interactive effects of temperature and drought on growth and toxicity. Both temperature and drought affected cassava physiology and chemistry. While temperature alone drove differences in plant height and above-ground biomass, drought and temperature 9 drought interactions most affected tuber yield, as well as foliar and tuber chemistry, including C : N, nitrogen and cyanide potential (CNp; total cyanide released from cyanogenic glucosides). Conditions that most stimulated growth and yield (well-watered 9 high temperature) effected a reduction in tuber toxicity, whereas drought inhibited growth and yield, and was associated with increased foliar and tuber toxicity. The magnitude of drought effects on tuber yield and toxicity were greater at high temperature; thus, increases in tuber CNp were not merely a consequence of reduced tuber bio-mass. Findings confirm that cassava is adaptable to forecast temperature increases, particularly in areas of adequate or increasing rainfall; however, in regions forecast for increased incidence of drought, the effects of drought on both food quality (tuber toxicity) and yield are a greater threat to future food security and indicate an increasing necessity for processing of cassava to reduce toxicity.

Bookmarks Related papers MentionsView impact

Rising sea levels are threatening agricultural production in coastal regions due to inundation an... more Rising sea levels are threatening agricultural production in coastal regions due to inundation and contamination of groundwater. The development of more salt-tolerant crops is essential. Cassava is an important staple, particularly among poor subsistence farmers. Its tolerance to drought and elevated temperatures make it highly suitable for meeting global food demands in the face of climate change, but its ability to tolerate salt is unknown. Cassava stores nitrogen in the form of cyanogenic glucosides and can cause cyanide poisoning unless correctly processed. Previous research demonstrated that cyanide levels are higher in droughted plants, possibly as a mechanism for increasing resilience to oxidative stress. We determined the tolerance of cassava to salt at two different stages of development, and tested the hypothesis that cyanide toxicity would be higher in salt-stressed plants. Cassava was grown at a range of concentrations of sodium chloride (NaCl) at two growth stages: tuber initiation and tuber expansion. Established plants were able to tolerate 100 mM NaCl but in younger plants 40 mM was sufficient to retard plant growth severely. Nutrient analysis showed that plants were only able to exclude sodium at low concentrations. The foliar cyanogenic glucoside concentration in young plants increased under moderate salinity stress but was lower in plants grown at high salt. Importantly, there was no significant change in the cyanogenic glucoside concentration in the tubers. We propose that the mechanisms for salinity tolerance are age dependent, and that this can be traced to the relative cost of leaves in young and old plants.

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Australian journal of plant physiology

Bookmarks Related papers MentionsView impact

Journal of experimental botany, Jan 19, 2015

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