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Bioenergy

The superplant project

Experts discuss how to improve sugarcane

MIGUEL BOYAYANIn the future, sugarcane should yield twice as much, store more sugar in a more easily degradable structure, resist pests and herbicides, require less water to grow and adapt to warmer weather and to air with more carbon dioxide (CO2). It will possibly also become a factory of substances that it does not produce normally. This, at least, will be case if it is up to the researchers that met at FAPESP’s headquarters in São Paulo, in March, during the Bioen workshop on Sugarcane Improvement (the presentations can be found at www.fapesp.br/bioen). “The future seems exciting and the prospects, encouraging”, optimistically stated Paul Moore, an American who has been living in Hawaii for 42 years and who is one of the icons of sugarcane science. The truth of the matter, however, is that the road to ideal sugarcane will be long.

If they materialize, the prognoses of this researcher from the Agricultural Research Center of Hawaii will have major consequences. According to the experts, more efficient sugarcane would help fight global warming, deforestation and air pollution. It might also help to deal with the energy crisis that would ensue from limiting the use of oil products and from the planet’s population growth.

Moore said that several factors currently limit sugarcane productivity: soil features, diseases, insects and climate. If all conditions are perfect, what sets the limit for the plant’s productivity is its own physiology: sugarcane can only store 6% of the solar energy to which it is exposed. Nevertheless, productivity under experimental conditions is no greater than half of this theoretical potential, indicating it would be possible to increase sugarcane yield by improving plantation conditions. According to him, the ideal is to go beyond: to think simultaneously about the environmental parameters and the plant’s intrinsic limitations and, perhaps, even raise its maximum productivity. A gigantic task, but he says he is optimistic about it because he has been monitoring scientific advances over the last few decades. “When I began my career in Hawaii, 42 years ago, nothing was known about sugarcane genes. We didn’t even know how to study such a complex genome. We have since taken many strides forward”, he stated.

Rosanne Casu, from Csiro (Australia’s Commonwealth Scientific and Industrial Research Organization) and Derek Watt, from Sasri (South-African Sugar Research Institute), agree. They were involved in some of the early effort to unravel sugarcane DNA, whose results were included in an international genetic database (GenBank) from 1996 to 1998 by South Africa, and by Australia and Brazil (with the Sucest Project, financed by FAPESP) in 2003.

Now that some years have gone by after the sequencing of sugarcane’s express genes, we are still far from being able to say that we know this plant’s genetic makeup. “We’re still finding genes and trying to discover the function of each”, says Rosanne. The researchers use the better known genomes of plants that have some similarity with sugarcane, such as sorghum and rice, as a basis. But the sugarcane genome is far more complex, with about ten copies of each gene instead of the usual two found in most multi-cell organisms. “And some of the sugarcane genes have no similar counterparts in other plants”, she adds.

Describing the genome is not an objective per se. The Australian researcher uses this information to understand why a young sugarcane plant does not store much sugar. Rosanne discovered that genes related to transporting sugar into the cells are more active in the mature sections of the stem than in the young sections, which explains why the base of the plant has more sugar. Understanding the details of this metabolism may one day allow us to manipulate these genes so as to induce the plant to store more sugar along a longer portion of its stems.

However, storing more sugar in the entire plant may turn out to be unfeasible. Derek Watt tries to reveal the relation between photosynthesis, whereby the leaves transform solar energy into vegetable biomass, and the accumulation of sugar: why does sugarcane store less in the plant’s younger parts? In one experiment, his group kept the sugar produced in the leaves from being carried to other parts of the plant, creating an artificial concentration of sugar. The result was that the genes responsible for photosynthesis were inhibited – something that Watt, along with several colleagues, is now trying to map in greater detail. For the time being, the South African geneticist is not thinking about the application of this knowledge: as far as he is concerned, it is merely high-grade basic research of interest per se.

Understanding the physiological balance between sugar and photosynthesis before thinking about manipulations is of the essence. Given the genetic, biochemical and physiological complexity of most of the plant’s characteristics, Rosanne and Watt agree that the first advance in the improvement of sugarcane will be its resistance – to disease, she believes, or to herbicides, according to him. One difficulty involved in the development of new varieties is the time the process takes. According to Glaucia Souza, from the Chemistry Institute of the University of São Paulo (USP) and Coordinator of FAPESP’s Bioen Program, genetic tools may shorten the time it takes to select new plant characteristics, a process that currently takes about 12 years.

Still, it will not be simple. The improvement programs introduce genetic modifications in sugarcane plants, but there is no way to apply these changes to specific genes. Additionally, one must grow the plants and wait for them to develop and for the characteristics to become apparent. Knowing which genes are responsible for the sought-after transformations – such as resistance to disease or to drought – may allow us to select plants even before they grow. Thus, Glaucia is describing the differences in genetic activity – the so-called transcriptome, the map of active genes – between the plants that grow in irrigated plantations and those that have suffered from a shortage of water, or hydric stress. According to her, producing drought-resistant plants is essential in Brazil, where 65% of the land available for planting sugarcane consists of pastureland with a protracted dry season. When the intention is to produce energy, it is not enough to merely understand the plant’s reaction to a water shortage. Glaucia plans to integrate the network of genes connected with water use and accumulation of sugar, a major study that will take a long time (and demand a lot of money) until it yields results. She will have the aid of the International Consortium for the Sequencing of the Sugarcane Genome, which is comprised of Brazil, Australia, the United States, South Africa and France.

MIGUEL BOYAYANTransgenic work
Most of the genetic manipulation of the Bioen Program takes place in the laboratory of the agronomic engineer Helaine Carrer, from USP’s Luiz de Queiroz School of Agriculture (Esalq). To obtain transgenic sugarcane, her team bombards sugarcane cells with minuscule gold spheres lined with DNA fragments, or infects them with bacteria capable of incorporating into the sugarcane those genes that are of interest. One of the modifications she is working on consists of inserting a gene that interferes with programmed cell death (apoptosis) in stressful situations. She has already produced plants with strong roots that tolerate stress better and is now analyzing whether these plants remain vigorous even when there is little water. It is still necessary to make the process more efficient to see how it performs in actual sugarcane plantations. Helaine, however, is moving beyond this in her plans to control sugarcane genes. The plant grows fast, is efficient in fixing carbon from the atmosphere, produces large amounts of biomass and has a developed system for storing substances, all of which mean it is a promising bio-factory, one that might produce biodegradable plastics or other substances. “But we haven’t yet managed to make it produce a satisfactory amount of these compounds”, she tells us.

Regardless of how well researchers know the techniques for altering genetic material, sugarcane has been beating them in this battle: somehow, out in the field, the plant manages to inhibit the activity of the inserted genes. They may be incorporated into the sugarcane genome, but it is as if they were gagged and bound. That is why agronomic engineer João Carlos Bespalhok, from the Federal University of Paraná, believes we will be unable to produce commercially viable transgenic sugarcane in less than five years. He belongs to Ridesa, the Inter-University Network for Sugar and Alcohol Development, which comprises 11 federal universities in the entire country and which has access to half of the area of Brazilian sugarcane plantations for its studies.

“Thousands of transgenic lineages have already been produced, but none became commercial”, tells us Robert Birch, an Australian from the University of Queensland. He has studied the artifices that the sugarcane plant turns to in order to silence strange genes and says that he has developed gene design rules that overcome this difficulty. However, for patent-related reasons he did not discuss these rules. “I don’t think I’m the only one who was successful in this; probably other researchers have also managed to do it, but they still can?t divulge it,? he said. In any event, he expects to publish his method shortly, to be used in any biotechnology laboratory. The techniques employed by Birch, a global authority when in it comes to the genetic engineering of sugarcane, enable him to suggest an interesting way to increase the amount of sugar stored by the plant: introducing a gene that transforms sucrose, the natural sugar of cane, into a type of sugar that the plant does not recognize, which it therefore continues to produce and store beyond the normal limit.

Adapted
All this is not only about inventing sugarcane that is different from the natural kind. Rowan Sage, a Canadian from the University of Toronto, shows that one must understand the biochemical processes that limit photosynthesis in the environment that is of interest. In each place, the plant behaves differently. Moreover, the climate is changing too fast for natural selection to act. He found that the enzyme RuBisCo, essential for photosynthesis, is produced in excess when temperatures and carbon dioxide concentrations are higher – circumstances that are becoming increasingly common in different parts of the world as a result of global climate changes. Therefore, under these circumstances, he suggests resorting to genetic engineering to limit the production of RuBisCo, saving nitrogen that can be redirected to other plant functions, such as increasing biomass productivity. “And increasing sugarcane yield while leaving the plantation area unchanged is a great service to environmental conservation”, adds Sage.

An increase in photosynthesis , given the rising carbon dioxide in the atmosphere, is one of the favorite subjects of biologist Marcos Buckeridge, a professor at USP and a Bioen coordinator. He found that sugarcane photosynthesis becomes more efficient when there are high CO2 concentrations (see Pesquisa FAPESP, issue 157). This time, he talked about another aspect of the physiology of sugarcane: the effects of the hormone gibberellin stimulate multiplication and the lengthening of the sugarcane cells, which thereby acquire more space for sucrose storage.

Csiro’s Graham Bonnet, from the UK, showed that, depending on its environment, the plant resorts to different strategies to distribute the carbon it absorbs. By limiting the irrigation of plants in a hothouse, he created sugarcane 41% smaller, but that can maintain most the plant’s photosynthesis capability (81%). In these plants, he found that the leafy mass was 37% smaller while the amount of sucrose stored was 27% greater than in plants of normal size. He also discovered that sugarcane can have a genetic potential to store more sucrose and that this can be detected in the plant’s leaves while it is still quite small.

The two days of scientific presentations closed with Robert Henry, an Australian from Southern Cross University, and Augusto Garcia, from Esalq. Henry showed how to get a huge volume of genetic data and Garcia presented software that he developed to produce genetic maps. What became evident was the magnitude of the group’s undertaking in the exploration of sugarcane’s genetics and physiology, besides the relations between the plant and the environment. Still, Paul Moore was optimistic, “There are lots of brilliant young people that will manage to establish a dialogue between geneticists and physiologists and drive this field of research forward quickly.”

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