Orange sweet potato champions biofortified foods in Africa

Two Ugandan children dig in to a plate of orange sweet potato (Credit: HarvestPlus)

According to a study published in the Journal of Nutrition this month, eating orange sweet potato reduces the prevelance of vitamin A deficiency in children in Uganda and Mozambique. Vitamin A is critical for the development of good vision as it is an essential component of rhodopsin, a pigment in photoreceptor cells in the eye. Consequently in poor communities in Africa and south-east Asia, where diets poor in vitamin A are widespread, vitamin A deficiency is the leading cause of preventable blindness. Healthy levels of vitamin A are also necessary for normal organ formation and maintenance. Orange-fleshed sweet potato varieties contain more than 50-fold more β-carotene, which is converted to vitamin A after ingestion, than the yellow or white varieties commonly eaten in African countries.

The study monitored the effects of the Orange Sweet Potato (OSP) project, which was funded by the Bill and Melinda Gates foundation and coordinated by HarvestPlus. The conclusions predict a promising future for the use of biofortified foods bred for increased nutritional value. It was the first large-scale study of its kind, involving 24 000 households from Uganda and Mozambique. Nutritionists and farmers educated communities on the health benefits of orange sweet potato and on growing, storing, and commercialising orange sweet potato crops. Local women were also given recipes and information about hygiene practices. (more…)

Synthetic enzyme reduces lignin content

Public domain image. Source: Glazer, A. W., and Nikaido, H. (1995). Microbial Biotechnology: fundamentals of applied microbiology. San Francisco: W. H. Freeman, p. 340. ISBN 0-71672608-4

Highlighted article: Kewwi Zhang, Mohammad-Wadud Bhuiya, Jorge Rencoret Pazo, Yuchen Miao, Hoon Kim, John Ralph, and Chang-Jun Liu (2012) An Engineered Monolignol 4-O-Methyltransferase Depresses Lignin Biosynthesis and Confers Novel Metabolic Capability in Arabidopsis. Plant Cell Preview.

Zhang et al. reduce lignin content by introducing an artificial enzyme to the cell wall biosynthesis pathway. This is the first time synthetic biology has been used to change cell wall structure, which is usually modified by changing the expression of endogenous enzymes or introducing a protein from another organism. In fact at the moment, synthetic biology is not a common method of manipulating any plant pathway.

Relevant background

public domain image, courtesy of Chino

Lignin is one of three components of secondary cell walls. It is the part which makes extracting sugar from the cell wall, for example for second generation biofuel production, difficult.

Lignin is made up of three monolignols: coniferyl, sinapyl, and p-coumaryl.

They are synthesised in the cytosol and transported to the cell wall. At the cell wall, the monolignols are oxidised, causing their phenol group to become radicalised. The phenoxy radicals polymerise to form the lignin macromolecule.

The Liu lab had the idea of preventing monolignol oxidation by methylation of the phenol group so that the phenoxy radicals were prevented from forming. Their first attempt was to synthesise a selection of monolignol 4-O-methyltransferases (MOMTs). The artificial MOMTS were fusions of two naturally occurring enzymes: lignin biosynthesis pathway methyltransferase COMT, which does not have any 4-O-methyltransferase activity; and fairy fan enzyme isoeugenol O-methyltransferase, which catalyzes 4-O-methylation of isoeugenol and eugenol, but doesn’t affect monolignols. Although several of these artificial enzymes were able to 4-O-methylate monolignols as expected in vitro, they had no activity in vivo.

Results

Zhang et al. used MOMT3, a promising enzyme from their earlier work, as a starting point. (more…)

Transcription factor-like effectors (TALEs)

Ubud, Bali by Mee Lin Woon; DNA Sequence by schulergd. Via stock.chng

Background

Xanthomonas spp. are plant pathogens that modulate their host’s gene expression in order to facilitate infection. They do this using transcription activator-like effectors (TALEs). Two domains are conserved in TALEs: an N-terminus, required for type III secretion into the plant cells; and a C-terminus with transcription factor activity. In the middle is a set of tandem repeats of amino acids, which mediates binding to host DNA.

As the binding and effector domains of TALEs can be customised, the possibility of using them for molecular and synthetic biology has been explored for some time. They have been used to change gene expression in plants, yeast, and even human cells.

TALEs have been adapted by researchers to make TALE nucleases (TALENs) – TALEs attached to a FOK1 nuclease domain. TALENs work in pairs that flank either side of the target site so that the nuclease domains meet at the point of cleavage. The nucleases cause a double-stranded DNA break, which is fixed imperfectly, causing an insertion or deletions.

In May this year, a paper was published demonstrating the huge impact TALEs could have on agriculture. Li et al. prove that transcription activator-like effector nucleases (TALENs) can be used to render rice resistant to the major agricultural pathogen, Xanthomonas oryzae pv. Oryzae (Xoo). (more…)

Views on synthetic plant products at the New Phytologist Synthetic Biology Workshop

The three day 4th New Phytologist Workshop on Synthetic Biology started on Wednesday 6th June, and we waited until after the Thursday afternoon coffee break to hear a presentation on plant synthetic biology. It was obvious that plant synthetic biology is not yet as sophisticated as synthetic chemistry and microbiology, and the reasons were implied in many of the talks. Plants are multi-cellular, have weeks-long life cycles and their products cannot simply be skimmed off or distilled from a vat of cells.

Rob Edwards (University of York) was quick to defend plant synthetic biology when I put this to him, pointing out that plant plastids are a means both of expressing a transgene and storing its possibly toxic product, all without affecting the rest of the cell. Plants can be grown cheaply, particularly if engineered to do so, although extracting the product may be expensive and difficult. On the other hand, synthetic biology may be used to enhance the flavor, fragrance or appearance of a fruit or flower and in that case the plant itself is a high-value product which requires no extraction.

While Rob Edwards’ SPPI-net focuses on synthetic biology for non-food plant products, he stated that genetically improved food crops can have great effects. Golden rice has the potential to help prevent blindness in areas where communities living on rice-based diets suffer from vitamin A deficiency, and soybean containing high omega-3 fatty acids can improve cardiovascular health. (more…)

New Phytologist Synthetic Biology Workshop: SynBio toolboxes for your lab!

Categories: synthetic biology
Comments: No Comments
Published on: June 28, 2012

Of more immediate practical use to the GARNet community than the technology described here are toolkits presented at the 4th New Phytologist Workshop by Susan Rosser (University of Glasgow) and Keith Saunders (John Innes Centre).

Violacein

Susan Rosser presented a soon-to-be-published multi-gene assembly kit based on synthetic integrons – ‘Syntegron’. Like existing kits for manipulating DNA, it involves cassettes which top and tail each gene or section of DNA. Unlike other kits, it will be open source and allows for many genes, even a whole pathway, to be assembled, shuffled if required, and expressed. It has been demonstrated to work on the 5-gene violacein pathway which was put, complete and functioning, into E. coli in just 5 days. I’m pretty sure this protocol will be a hit, and it will be an excellent method for a group to use when they try out synthetic biology for the first time.

Keith Saunders presented another gene transfer method, the CPMV-HT expression system which won the BBSRC Innovator of the Year award for Professor George Lomonossoff and Dr Frank Sainsbury. Their system is based on empty virus-like particles (eVLPs), made from modified cow pea mosaic virus (CPMV). (more…)

New Phytologist Synthetic Biology Workshop: SynBio toolboxes for de novo peptide synthesis

Categories: synthetic biology
Comments: 2 Comments
Published on: June 26, 2012

As exciting as this research in this post is, to me as a humble traditional molecular biologist the most impressive ‘toolboxes’ were the truly synthetic ones involving no genes at all. Dek Woolfson (University of Bristol) and Samuel Stupp (Northwestern University, USA) presented astonishing work on custom peptides.

The Woolfson group is working towards making a toolbox for building proteins. They chose to work on α-helical coiled-coils because these peptide structures have that essential orthogonality built in – the correct peptides form coiled-coils irrespective of the surrounding domains, which can then be customised to fit the designer’s requirements. The group is now able to synthesise a number of structures using coiled-coils.

from Moutevelis and Woolfson (2009) JMB 385:726 (Click on image to go to paper)

(more…)

Plant Sentinels and Robolobsters at the New Phytologist Synthetic Biology Workshop

Categories: synthetic biology
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Published on: June 15, 2012

In the rainy aftermath of last week’s Jubilee celebrations, a group of synthetic biologists gathered in Bristol for the 4th New Phytologist Workshop. Participants were treated to three days of stimulating talks on a wide range of topics all considered to be ‘Synthetic Biology.’ GARNet was there, and will be posting highlights, like the plant sentinel in the video below.

Video courtesy of the Medford Lab at Colorado State University.

So what is synthetic biology? The consensus definition of synthetic biology, or synbio, appears to be  ‘the design and construction of novel biologically based parts, devices and systems from first principles, or the re-design of existing natural systems for useful purposes.’

Synbio differs from traditional science by viewing biological systems as an engineer would view a machine – something to be created, not necessarily something that needs to be fully understood. The process consists of a cycle of hypothesis, computer aided design, production of molecule or system, analysis of results, repeat. Creating synthetic biology tools and resources (libraries of promotors, active sites, peptide sequences … the list is endless) of course involves a great deal of understanding of biological systems, but to an extent the unknown remains unknown, the most important thing is that you understand how the building blocks of your synthetic system work.

(more…)

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