”It’s soft, not so stiff, and it has a high potential to become something important in the future.”
Researcher Mariette Andersson describes the material that she and her colleagues have made from the starch of a genetically modified potato. This plastics can be composted after using it. Furthermore, the starch has now been used as a part of a composite material. By tailoring mixtures of plant proteins and starch, molecularly and biochemically, one can design sustainable materials for various uses including packaging and plastic film.
In two studies Mariette Andersson and colleagues have tested how this particular potato starch works with proteins from wheat (gluten, gliadin and glutenin which are possible components of the new material). The idea is to develop a stretchable and strong material. They used either glycerol or glycerol + water as plasticizer and extruded the plastics at two different temperatures, 110 °C and 130 °C. In the analysis, they could see that the different proteins reacted in different ways in combination with the starch. In some cases, the material became relatively soft and flexible, and in other cases, stronger and less soft.
The higher temperature induced a higher degree of protein cross-links. With glycerol + water as plasticizer, the starch got improved gelatinous properties, and the material became stronger, more stretchable and easier to process (compared to using only glycerol).
They also tested what happened to the protein structure at the nanometer level (a level that is one millionth of a millimeter), the mechanical strength of the plastics, and if the material let oxygen molecules to pass through. Some of the gliadin molecules adopted an unusual hexagonal structure in mixtures with starch, and this structure made the material stronger. The combinations of protein + starch worked well as an oxygen barrier.
Ordinary potato starch, consists of molecules with both short and long chains of glucose. The starch molecule amylose has long linear chains of glucose while the amylopectin molecule has a highly branched structure. Native potato starch contains 20-30 percent amylose and 70-80 percent amylopectin.
Using biotechnology, the researchers decreased the levels of two enzymes regulating the branching of starch molecules in potato. This modification increased the glucose chain length of the amylopectin molecules. Thanks to this, the starch got the fiber-like properties that make it suitable as a component of a new environmentally friendly packaging material.
Researchers at the Swedish University of Agricultural Sciences, KTH Royal Institute of Technology, Innventia AB, MAX IV Laboratory in Lund and Institut Polytechnique in France did this study with funding from Mistra Biotech, TC4F, Lyckeby Starch AB, Formas and Partnerskap Alnarp.
Muneer, F., Andersson, M., Koch, K., Hedenqvist, M. S., Gällstedt, M., Plivelic, T. S., Menzel, C., Rhazi, L., & Kuktaite, R. 2016. Innovative Gliadin/Glutenin and Modified Potato Starch Green Composites: Chemistry, Structure, and Functionality Induced by Processing. ACS Sustainable Chemistry & Engineering.
Muneer, F., Andersson, M., Koch, K., Menzel, C., Hedenqvist, M. S., Gällstedt, M., Plivelic, T.S., & Kuktaite, R. 2015. Nanostructural morphology of plasticized wheat gluten and modified potato starch composites: relationship to mechanical and barrier properties.Biomacromolecules, 16: 695-705
Talking about potato, Sweden, Norway and Finland have a lot in common. We prefer the floury potato cultivars, while elsewhere in Europe people prefer the firmer potatoes. We have the cold northern climate in common, with long days in the short summer, and problems with the same kind of pathogens. On the other hand we have no major problems with drought. Therefore, drought tolerance is not a particularly prioritized potato trait in this region.
With this in mind, researchers at SLU suggest that the three countries join hands and cooperate to develop new better potato cultivars.
In a scientific paper, researcher Dennis Eriksson and his colleagues presented an overview of the potato cultivation, consumption and potato processing in Fennoscandia (Sweden, Norway and Finland). The development of new potato varieties have diminished in Norway and Sweden, and ceased altogether in Finland.
– This is a shame because potato is the highest yielding food crop here. At the same time, potato is an irreplaceable part of our food culture, and the potato breeding has a long and proud history in our countries, says Dennis Eriksson.
Having previously decreased for decades, potato consumption has remained steady at just above 40 kg per person and year in Sweden the last 20 years. Do we want to continue to eat potatoes in the future? Can we grow potatoes more sustainable than today? Yes, scientists believe so, but sustainability requires smart strategies.
We need potato varieties that do not need to be sprayed with fungicides. All the varieties we grow today are susceptible to late blight caused by the pathogen Phytophthora infestans. The spraying is bad for the environment and makes potato cultivation more expensive. Potato varieties also need to eventually be adapted to a future climate, predicted to become warmer and wetter in the north. And more pests are expected to find their way to this region as the climate changes.
– A high and stable potato production, under the particular conditions that we have in the north, is crucial. This requires an early tuber maturity due to the short summer season. And, in addition to late blight, there are other potato diseases that are common in this region, says Dennis Eriksson.
The researchers say that the Fennoscandian market is too small to motivate the profit-driven breeding companies to invest in potato breeding that matches the specific requirements of this region. Consequently we rely on public investment to develop new varieties, and such financial support must be maintained for a long time.
In their study, the researchers present seven reasons for public investment in potato breeding in the Fennoscandian region:
Once you have a new potato variety, and want to test and commercialize it, it might be a good idea to collaborate with an established plant breeding company.
– The advantage of this would be that the testing of cultivars can be done on a larger scale and more efficiently. This kind of collaborations could provide access to an infrastructure that would not be available otherwise. The payment for these services could take different forms. In Norway the plant breeders at Graminor have an agreement with the private partner Agrico, giving Graminor the right to market the cultivars at a national level while Agrico has gained the right to market the cultivars abroad, says Dennis Eriksson.
The plant breeding company Graminor is largely financed by the state but it also has private part-ownership.
Eriksson, D., Carlson-Nilsson, U., Ortíz, R., & Andreasson, E. (2016) Overview and breeding strategies of table potato production in Sweden and the Fennoscandian region. Potato Research, 1-16.
When a plant is attacked by an insect or a pathogen, an array of responses start. Some of those responses can be very specific to whom the attacker is, and they have evolved during the evolutionary arms race between the plant species and the pest. The researchers have performed an analysis to find out more about which plant proteins are involved in what kinds of plant defence systems, during the attack of the oomycete Phytophthora infestans (that causes potato late blight). They have looked at the composition and levels of specific proteins in leaves of potato, when the plant protects itself against P. infestans. For instance, a protein annotated as a sterol carrier protein shows high abundance in plants that are under attack, which is interesting, and in a way logical, since the oomycete relies on the plant host for sterols.
In addition to the sterol carrier protein, they found an increased abundance of several RNA binding proteins as part of the defence response. This kind of proteins have a role in a great number of processes in the cells and in the post-transcriptional control of gene expression. Plants have a wide variety of ways to defend themselves, at different stages of a pathogen attack. Plants can recognize so called pathogen-associated molecular patterns (PAMPs) that result in a first level of basic defence named PAMP triggered immunity (PTI), inducing the transcription of defence related genes. This PTI defence can be suppressed by crafty pathogens that secrete molecules called effectors into the plant cell. To counteract this, some plants have in their turn evolved proteins that recognize effectors and by that initiate a second level of defence called effector triggered immunity (ETI).
The researchers found that some changes of protein abundance are only regulated in PTI, and not at all in ETI interactions. One such potato protein has a domain resembling a part of a protein found in barley. And that barley protein is involved in regulating the plant’s basic resistance. There was also an increased level of a glyoxysomal fatty acid beta-oxidation multifunctional protein in the PTI interaction. It has earlier been shown that an Arabidopsis mutant lacking that protein had a reduction of jasmonic acid accumulation, indicating that an increase of this protein might contribute to a generation of signalling molecules needed for the PTI response. Jasmonic acid is a hormone well known for its function in regulating plant responses to stress.
Another interaction-specific change that the researchers noticed was that a family of catalase proteins only were upregulated in the ETI interactions. Catalase related genes have previously been found to be regulated by both biotic and abiotic stresses, for example in sugarcane during plant–pathogen interactions. A few proteins were regulated in only one of the ETI interactions, for example a number of histones, which are important in the package of DNA in cell nuclei. Hopefully the results can be used in future potato pre-breeding to predict sustainable combinations of resistance genes in the plant.
Resjö, S. Zahid, MA, Burra, DD., Lenman, M., Levander, F. & Andreasson, E. 2019. Proteomics of PTI and two ETI immune reactions in potato leaves. International Journal of Molecular Sciences 20: 4726 doi: 10.3390/ijms20194726
Mariette Andersson and her colleagues have found a new way of using the so-called genetic scissor Crispr/Cas9 so that the DNA encoding it does not end up in the genome of the edited potato plant. Thereby they have further developed the method of genome editing of potato.
Instead of allowing the DNA, coding for the scissor, to code for the RNA and protein that make up the Crispr/Cas9-complex inside the plant, temporarily, the RNA and the protein complex are produced outside the plant before allowing the complex to do the job in the cell.
The researchers took cells from the potato, removed the cell walls and added the Crispr/Cas9 complex (i.e. the gene scissor and not the DNA that encodes for the scissor). Then the cell cultures were grown into plants. The researchers checked that the mutations were in the right places, and examined whether any DNA was accidentally inserted into the genome. With this new "DNA-free" method, the researchers produced two potato clones with mutations in all four alleles of the gene (as most cultivated potatoes this was a tetraploid, thus having four sets of chromosomes) without any accidentally added DNA.
Different labs all over the world are working to adapt the Crispr/Cas9 method to work efficiently and with great precision in various plants and animals. This study is a step along the way to refine the potato genome editing technology.
The gene the researchers chose to edit in the potato is involved in the biosynthesis of the amylose starch molecule. The gene got a mutation that prevented the production of amylose in the plant, and instead more of the amylopectin starch molecule was produced.
Andersson, M., Turesson, H., Olsson, N., Fält, A.S., Ohlsson, P., Gonzalez, M.N., Samuelsson, M. & Hofvander, P. 2018. Genome editing in potato via CRISPR‐Cas9 ribonucleoprotein delivery. Physiologica Plantarum doi: 10.1111/ppl.12731
A novel potato that contains modified starch has been developed by researchers in plant breeding, and now, a study carried out by food scientists shows that the modification has resulted in a healthier starch.
Considering that we eat a lot of potato in Scandinavia, potato starch makes up a large part of the energy in many people’s daily diet. If a new potato with a more resistant starch would be commercially available in the future, it might have a positive impact on public health. Resistant starch is a dietary fiber with benefits for our bodies. As such, it lowers the glucose levels and the insulin responses, increases fecal output and reduces the fecal transit time. It decreases the calorie content in foods which is related to weight loss, and it promotes the growth of beneficial gut bacteria.
Such a new potato was successfully developed by plant researchers by down-regulating two starch branching enzymes. Potato starch usually consists of 25 percent amylose (linear molecules) and 75 percent amylopectin (highly branched molecules). The objective with this modification was to produce a potato with high amylose content.
In a study, PhD student Xue Zhao and her supervisors Roger Andersson and Mariette Andersson show that a high content of amylose gives a high content of resistant starch in this cooked potato. But they also found something else.
– The down regulation of the enzymes had an effect on amylopectin structure where the outer chain-length of amylopectin was much longer than in the unmodified potato cultivar, Xue Zhao explains.
This unique amylopectin has properties that are similar to amylose. After cooking, the modified amylopectin recrystallizes, and after that it is not split as easily as the ordinary potato starch, which means it is more resistant and takes longer time to digest.
– An additional analysis revealed that one extra day of cold storage gives a further increase of resistant starch content, since amylopectin needs some time to get recrystallized, says Xue Zhao.
The study showed that the resistant starch content was influenced both by the amylose/amylopectin ratio and by the amylopectin structure. These are important findings in order to design functional starch and healthier food.
The potato was developed using genetic modification. At the moment the researchers are working on a new similar “high amylose” potato using the genome editing technique Crispr/Cas9.
Zhao, X., Andersson, M. & Andersson, R. 2018. Resistant starch and other dietary fiber components in tubers from a high-amylose potato. Food Chemistry 251: 58-63
Phytophthora infestans, an oomycete, is the most harmful pathogen of potato. It causes the disease late blight, which generates increased yearly costs of up to one billion euro in the EU alone, and it is tough to control. Svante Resjö and colleagues tried to find out more about how the late blight pathogen P. infestans acts during the disease infection, and managed to identify proteins that seem to be of high importance for the pathogen at different life stages.
Among 10 000 peptides, from over 2000 proteins, they found 59 interesting ones that were highly abundant in the pathogen at pre-infectious life stages, i. e. in its germinated cysts and the cells that penetrate into the potato plant. A large majority of these proteins have not been recognized as being part of this infection process before, but based on their similarity to other proteins, with known function, the researchers could predict that they play roles in transport, amino acid metabolism, pathogenicity and cell wall structure modification.
The researchers also analyzed the expression of the genes encoding nine of these proteins and found an increased level during disease progression, in agreement with the hypothesis that these proteins are important for the infection to happen. Among the nine proteins was a group involved in the pathogen’s struggle to modify and hold on to the cell wall structure. Silencing of these genes resulted in reduced severity of the infection, additionally indicating that these proteins are important for pathogenicity.
Resjö, S., Brus, M., Ali, A., Meijer, H.G.J., Sandin, M., Govers, F., Levander, F., Grenville-Briggs, L., Andreasson, E. 2017. Proteomic analysis of Phytophthora infestans reveals the importance of cell wall proteins in pathogenicity. Molecular and Cellular Proteomics 16:1958-1971