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Plant Artificial Chromosome Technology

By | Blog, Future Directions

Established GM technologies are far from perfect

The first genetically modified (GM) crops were approved for commercial use in 1994, and GM crops are now grown on over 180 million hectares across 29 countries. The most used forms of genetic modification are systems that result in herbicide resistance or expression of the Bt toxin in maize and cotton to provide protection against pests such as the European corn borer. These systems both require few novel genes to be introduced to the plant, and allow more efficient use of herbicides and pesticides, both of which are harmful to the environment and human health. Current systems of genetic modification usually involve

Agrobacterium tumefaciens is used to genetically engineer plants in the lab. In nature this bacteria uses its ability to alter plant DNA to cause tumours.

Agrobacterium tumefaciens is used to genetically engineer plants in the lab. In nature this bacteria uses its ability to alter plant DNA to cause tumours. Image by Jacinta Lluch Valero used under Creative Commons 2.0.

the use of Agrobacterium vectors, direct transformation by DNA uptake into the plant protoplast, or bombardment with gold particles covered in DNA. However, current systems of transformation are far from perfect. Many beneficial traits such as disease resistance require stacking of multiple genes, something that is difficult with current transformation systems. Furthermore, it is essential that transgenes are positioned correctly within the host genome. Current systems of genetic modification can insert genes into the ‘wrong’ place, disrupting function of endogenous genes or having implications for down or upstream processes. An additional problem is that transfer of transgenes from one line to another requires several generations of backcrossing. However, the past two decades have seen great developments in microbiology. Many new tools and resources are now available that could greatly enhance the biotechnology of the future.

 

New technologies

Many new and emerging technologies are now available that could transform plant genetic engineering. For example, high throughput sequencing and the wide availability of bioinformatics tools now make identifying target genes and traits easier than ever. Technologies such as site-specific recombination (SSR) and genome editing allow specific regions of the genome to be precisely targeted in order to add or remove genes. Artificial chromosome technology is also part of this emerging group that could be of benefit to plant science. Synthetic chromosomes have already been used in yeast, and widely studied in mammalian systems due to their potential use in gene therapy. Although there have so far been no definitive examples in plants, work has been done in maize that shows the potential of the technology for use in GM crops.

 

Building an artificial chromosome

A minichromosomes is a small, synthetic chromosome with no genes of its own. It can be programmed to express any desirable DNA sequence that could encode for one, or a number, of genes. An ideal minichromosome would be small and only contain essential elements such as a centromere, telomeres and origin of replication. Once introduced into the plant the minichromosomes should be designed such that interference with host growth and development is minimal. A key requirement is that the chromosome is stable during both meiosis and mitosis. This would ensure introduced genes do not become disrupted or mutated during cell division and reproduction. Gene expression would therefore remain the same for many generations. Finally, the DNA sequence on the minichromosomes could be designed such that it is amenable to SSR or gene editing systems. This would allow re-design and addition of new traits further down the line.

 

Potential advantages of artificial chromosomes

Plant artificial chromosomes (PACs) have many advantages over traditional transformation systems. For example, to confer complex traits such as disease resistance and tolerance to abiotic stresses such as heat and drought, multiple genes are required. This is not easy with current methods of modification.

PACs could offer a new way to introduce beneficial traits to our crops plants and feed a growing population.

PACs could offer a new way to introduce beneficial traits to our crops plants and feed a growing population.Image by Seattle.Romer. Used under Creative Commons 2.0.

However, PACs allow an almost unlimited number of genes to be integrated into the host system. A further possibility that comes from being able to add multiple genes is the addition of new metabolic pathways into the plant. This could allow us to change the nutrients produced by a plant to benefit our diets. Additionally, in a contained environment, plants could be used as a cheap, sustainable way to produce pharmaceuticals. A second major benefit of PACs is that they avoid linkage drag. This is when a desirable gene is closely linked to a deleterious gene that acts to reduce plant fitness. Where this linkage is very tight even repeated backcrossing cannot separate out the genes. Design of new DNA sequences completely avoids this problem, and could allow us to select out detrimental traits from out crop plants.

 

Regulations for novel biotechnology

Emerging technologies pose new questions to policy makers regarding GM regulation. For example, the use of genome editing, whereby specific sites in the genome are targeted and modified, produces an end product with a phenotype almost identical to one that could be achieved through conventional breeding. This sets genome-edited crops apart from other transgene-containing GM material. For this reason many now argue that genome-edited crops ought not to come under current GM regulations. Much of this argument centres on whether or not to regulate the scientific technique used to produce a crop, or to regulate the end product in the field. For more information on genome editing including current regulations and consensus, see the links at the end of this article.

 

PACs pose a different set of problems entirely. Minichromosomes would be foreign bodies in the plant, and gene stacking within these introduces even more foreign genes than is possible with current technologies. This would require extensive assessment of both environmental and health effects prior to commercialization. Currently regulatory approval costs around $1-15 million per insertion into the genome. These heavy charges may discourage the further development of minichromosomes technology. However, with PACs it is possible that a particular package of genes could be assessed once, and then transferred into numerous cultivars. This would eliminate the requirement to individually engineer and test every cultivar, so perhaps saving time and money in the long term.

 

More information on genome editing:

Sense about science genome editing Q & A

The regulatory status of genome-edited crops

The Guardian article on genome editing regulation

A proposed regulatory network for genome edited crops in Nature

A recent workshop on the CRISPR-CAS system of genome editing was held in September 2015 by GARNet and OpenPlant at the John Innes Centre in Norwich, UK. You can read the full meeting report here.

 

 

 

 

 

 

 

 

 

 

 

GPC President Professor Bill Davies’ vision for the future

By | ASPB, Blog, Future Directions

Global Plant Council President Professor Bill Davies discusses his vision for the future of the GPC and its role in meeting some of the global challenges facing plant science and society today.

GPC President Professor Bill DaviesRaising the profile of plant science

As we face the task of sustainably feeding an ever-increasing global population, the issue of food security has never been more pressing, and of course, plant science plays a fundamental role in addressing this challenge. Professor Davies believes the GPC can have a major impact in raising the profile of plants in all parts of society, but perhaps most urgently with the policy makers who can drive investment into research.

He explains: “Plant science tends to have a lower priority with funding agencies. A number of years ago there was quite a lot of talk about plant science being a pretty mature subject and therefore we didn’t need much money for research. Fortunately the European Plant Science Organisation (EPSO) managed to convince the European Parliament and others that there was an important opportunity here, the funding continued and we’ve seen a lot of benefits from that – both in furthering plant science and enhancing food production”. He continues: “Raising the profile of plant science is key, and – more specifically – we need to think about ways in which, collectively, we could address some of these challenges”.

A global conversation

Genetic diversity research - CIAT

Image by Neil Palmer (CIAT). Used under: CC BY-SA 2.0

Professor Davies believes the GPC is well placed to tackle global problems on a worldwide scale, by providing platforms for member organizations and individuals to collaborate on a variety of issues: “There are some genuinely global challenges that the GPC could take on. We can try to provide more opportunities for people who might be interested in addressing things beyond the boundaries of their own national scientific societies”. He adds: “I’ve been a member of the Society for Experimental Biology (SEB) longer than I care to imagine, and it’s been a really important part of my life. It delivers a lot more than just good science. The SEB has made and continues to make a big effort to operate internationally, but there’s a limit, whereas there’s no limit for GPC.

“One of the things we’ve been talking about is whether there is more that we could offer societies, particularly in developing countries. Are we making resources available that can be as influential in Ghana, for example, as they might be in the United States? If there are opportunities to broaden the scope of that offering, particularly to address some of the areas where food security is a major issue, then we can do that and, I hope, help national societies in parts of the world where they are not as influential as they might be. I believe that there is strength in numbers.

“It seems entirely logical to me to address global challenges with a global organization”.

Building resources

One of the key goals of the GPC is to build up databases of information and resources that can be used by researchers, plant breeders, farmers and other agricultural stakeholders all around the world. This is being done both as part of the three main GPC initiatives (Diversity Seek, Biofortification, and Stress Resilience), but we are also collaborating with the American Society of Plant Biologists (ASPB) to launch an online platform for the plant science community this summer.

Gene bank - IRRI

Image credit: IRRI. Used under: CC BY 2.0

Professor Davies is keen to harness the power of the online community for cultivating a new excitement around plant science. He led a massive open online course (MOOC) about food security at Lancaster University last year, and was pleased to see how engaged the participants were. He explains: “We had 5000 students with a fantastic level of enthusiasm and commitment. At the end of it we were left with the feeling that people were keen to know more.

“My view is that if you listen to people talk about why they do the science they do, what’s involved, and to some extent how they do it, then I think you’re in a position to make a much more well-informed decision about the science in general or controversial issues, and to contribute to the debate”.

Professor Davies believes that the online plant science platform from the ASPB and GPC will provide useful resources for scientists, teachers and students alike: “I’m in this business because I was inspired by lecturers both as an undergraduate and in graduate school. If we can capture the drama and excitement of science, we can make it available to everyone. It’s a wonderful opportunity”.


Professor Bill DaviesProfessor William (Bill) Davies is the President of the Global Plant Council and Distinguished Professor of Plant Biology at Lancaster University, UK. His research into stress responses in plants and his involvement with many international projects aimed at improving global food security led to him being awarded a CBE award for services to Science in the 2011 Queen’s Birthday Honours list. For more information, click here.