Brassica Research Report: 2015

The Arabidopsis Research Roundup has been put to bed for 2015 so in the leadup to the Christmas we’ll take a look at some of the papers that have been published in 2015 by UK researchers working ondifferent plants.
Today we focus on Brassica species and by looking at papers from throughout 2015 this selection touches on a broad selection of research areas. Chronologically first is a study from Nottingham University that looks at the ability of Brassica rapa to take up specific elements, such as Zn, Ca and Mg. Secondly is a study that documents the parameters that make different cultivars of Brassica napus useful in biorefining. Thirdly we highlight where Brassica oleracea has been used both in preference to, and alongside Arabidopsis in a study that investigates meiotic recombination. Next is a study that investigates the relationship between leaf colour and insect herbivory. Finally we highlight a recent publication from the John Innes Centre that demonstrates the ability to generate gene-edited B.oleracea.
The varieties of Brassica
March

Blasco B, Graham NS, Broadley MR (2015) Antioxidant response and carboxylate metabolism in Brassica rapa exposed to different external Zn, Ca, and Mg supply.
J Plant Physiol. 176:16-24 http://dx.doi.org/10.1016/j.jplph.2014.07.029
Martin Broadley and Neil Graham from Nottingham University lead this study that investigates antioxidant response and carboxylate metabolism in Brassica rapa. The authors looked at these parameters in the presence of varying amounts of zinc, calcium or magnesium in experiments that aimed to simulate the response to deficiency or toxicity of these elements. Plants grown with high concentrations of these elements showed increased shoot biomass, hydrogen peroxide, total ascorbate and increasing activity of enzymes involved in removal of antioxidants. This indicates that B.rapa is particularly sensitive to high levels of these elements. The information provided in this study represents important baseline measurements that will aid the future characterisation of B.rapa TILLING lines, generated by the RevGenUK service at the JIC.

July

Wood IP, Wellner N, Elliston A, Wilson DR, Bancroft I, Waldron KW (2015) Effect of Brassica napus cultivar on cellulosic ethanol yield. Biotechnol Biofuels. 8:99. http://dx.doi.org/10.1186/s13068-015-0278-z Open Access
Keith Waldron (Institute of Food Research, JIC) leads this collaboration with the University of York that investigates how the sugar composition of Brassica napus alters its ability to be used as a source for biorefining. They found significant differences in the saccharification and fermentation yields after the processing of straw obtained from 17 different B.napus cultivars. Surprisingly glucan-rich straw was not correlated with higher saccharification or ethanol yields but rather the non-cellulosic components were more reliable indicators of substrate quality, with the amount of pectins and arabinogalactans having the greatest impact on saccharification. Ultimately this study finds that pectin concentration is most likely to determine to effectiveness of the cultivar in the production of bioethanol. This is important information for the future development of different dicot species for use in this aspect of biorefining.

July

Lambing C, Osman K, Nuntasoontorn K, West A, Higgins JD, Copenhaver GP, Yang J, Armstrong SJ, Mechtler K, Roitinger E, Franklin FC (2015) Arabidopsis PCH2 Mediates Meiotic Chromosome Remodeling and Maturation of Crossovers PLoS Genetics 11(7):e1005372 http://dx.doi.org/10.1371/journal.pgen.1005372 Open Access

Immunolocalisation of proteins during meiotic recombination in Brassica.
Immunolocalisation of proteins during meiotic recombination in Brassica.

Chris Franklin (Birmingham) is the leader on the UK-US-Austrian collaboration that looks at the role of the PCH2 protein during meiotic recombination. Although much of this study uses Arabidopsis mutant plants, the initial immunoprecipitations that led to identification of novel factors were performed using pollen mother cells from Brassica oleracea. Subsequently some important imaging also takes place in B.oleracea. The authors use structured illumination microscopy (SIM) to investigation the localisation of synaptonemal complex formation during meiosis and the close relationship between Arabidopsis and B.oleracea allowed the authors to use to same reagents fo these experiments. This paper was featured in an Arabidopis Research Roundup earlier in the year.

September.

Green JP, Foster R, Wilkins L, Osorio D, Hartley SE (2015) Leaf Colour as a Signal of Chemical Defence to Insect Herbivores in Wild Cabbage (Brassica oleracea). PLoS One 10(9):e0136884 http://dx.doi.org/10.1371/journal.pone.0136884 Open Access

This collaboration between York and Sussex Universitites is led by Sue Hartley and Daniel Osorio and look into the role that leaf colour plays in the defence response in wild cabbage. This aspect of plant physiology has been proposed as being important in defence against insect herbivory but this is the first instance where real data from wild populations has been obtained on this topic. The authors found that variation in leaf colour and brightness corresponded to particular glucosinolate levels as well as of the ability of certain herbivores to colonise the leaves. As might be predicted, leaves with lower levels of glucosinolate coincided with faster growth rates of lepidopteran larvae. However in a controlled experiment neither adult butterflies or adult aphids showed a preference for leaves of different colours. This therefore might suggest that although in the field herbivores may benefit from colonising leaves with lower defence chemicals (and an altered colour), the adults do not have the ability to select for these particular leaves, indicating that selection of leaves is either down to chance or other uninvestigated parameters.

November.

Lawrenson T, Shorinola O, Stacey N, Li C, Østergaard L, Patron N, Uauy C, Harwood W (2015) Induction of targeted, heritable mutations in barley and Brassica oleracea using RNA-guided Cas9 nuclease Genome Biol. 16:258. http://dx.doi.org/10.1186/s13059-015-0826-7 Open Access

An example of successfully gene edited Brassica. From Genome Biology
An example of successfully gene edited Brassica. From Genome Biology

This is a collaboration between Wendy Harwood, Cristobal Uauy, Nicola Patron and Lars Ostargaard from the John Innes Centre and the Sainsbury Lab in Norwich. Over the past few years, CRISPR-Cas technology has been presented as important technology to be used in the future generation of gene edited crops. However only a few studies have been published to date where this technology has been effectively used. This paper describes the use of CRISPR-Cas to generate specific mutations in both barley and Brassica oleracea. Across both species they identified targeted mutations in 10%-25% of the first generation plants although interestingly they were also able to identify B.oleracea mutants in the T0 generation. They also observed off-target activity in both species even though the designed guide RNAs contains mismatches with the incorrectly edited sequences.
This is important work demonstrating that this type of gene editing can be used to rapidly generate stable mutants in crop species. The creation of mutants in off-target genes is a potential concern from a regulatory perspective although can be viewed as a positive factor for targeting multigene families that do not have appropriate identical target sequences.



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