|Keywords:||Apomixis; Public institute; Socio-economic impact; Genetic engineering.|
|Correct citation:||Jefferson, R.A. (1994), "Apomixis: A social revolution for agriculture?" Biotechnology and Development Monitor, No. 19, p. 14-16.|
Among the many other advantages, apomictic food crops could eliminate the need of farmers in developing countries for yearly purchases of new hybrid seed. Richard Jefferson argues that especially public domain research into apomixis could generate new and versatile breeding strategies, available to the resourcelimited plant improvement community.
Shaping agriculture for both human needs and for environmental health
can be greatly accelerated by properly developing the trait of apomixis.
Apomixis is the phenomenon by which certain plants produce 'seed
without sex'. Introduction of this trait to crop plants would allow the
immediate fixing of the genetic makeup of any individual plant that
responded particularly well to a given environment or social need by producing
seed with identical genetic properties to the parent. This tool would enable
us to adapt plants to the environment, rather than the current necessity
for adapting the environment to the plants through intensive agricultural
practice. In contrast to today's hybrid technologies, it would make grain
and seed once again the same, restoring farmers to their role as innovators.
The introduction of this trait into crop plants would herald perhaps the
single greatest change in agricultural practice since the dawn of cultivation.
To achieve such a revolutionary impact, and to ensure that the impact is both environmentally and socially sound, the trait must be developed to have certain characteristics, and must be accessible to all people. We should develop a concerted, focused and strategic international research programme within the public domain to generate the trait de novo using molecular techniques.
What is apomixis
Plant reproduction occurs by complex and diverse mechanisms. Sexual reproduction is most common in flowering plants of agricultural importance. Male and female gametes (the pollen and the egg cells respectively) are separately produced with half the normal chromosome number. These combine during fertilization and further develop to give rise to a seed. This seed contains genes derived from both parents in a form that is distinct from both parents so that once that seed germinates a plant of unique genetic constitution is generated. By contrast, apomixis produces seeds through asexual processes. The genetic makeup of the seeds is identical to that of the mother plant. If the mother plant is well adapted to a particular environment or purpose, so will be the offspring.
Although many wild plants are naturally apomictic, for instance the common dandelion (Taraxacum sp.), very few crop species are apomictic. This is perhaps not surprising. Over the last thousands of years today's crop species were selected from amongst the numerous edible or fibrous plants by farmers. The criteria for such a choice almost certainly included the plant's ability to segregate variation: to reassort traits through sexual reproduction, and thus to improve under mass selection. This is the very property that apomixis prevents. Thus our small collection of modern day crops probably represents a biased population in favour of sexuality.
Potential impacts of apomixis
When apomixis is developed to meet stringent criteria the impact on agriculture could be sweeping and profound. Changes that could ensue are:
Shaping apomixis by a transgenic mechanism
It is becoming clear that de novo generation of the trait, i.e. synthesis of a suitable controllable apomixis through molecular biology, is a viable and productive avenue. Molecular biology and genetic engineering are often seen largely as tools to introduce an existing trait or gene into sexually incompatible species. However, the real power of these approaches lies in the ability to prise apart the underlying mechanism(s) of biological processes. With this level of understanding, adjustment and modification of biological processes by molecular intervention can lead to generation of entirely new traits.
For example, envision a scenario in which an apomictic gene 'cassette' can be generated through molecular biology that addresses the key constraints and opportunities outlined above. This cassette could be introduced into diverse crops where it would function to: (a) produce a fully functional egg cell with a full set of maternal chromosomes; (b) block the development of male sexual structures to avoid wastage of the plant's resources and to prevent uncontrolled spread of the trait; (c) allow development of the seed without any requirement whatsoever for pollination to avoid problems of pollination failure; (d) be conditional, where the default state is apomictic, but upon application of a nonproprietary, inexpensive natural compound, the trait is fully suppressed so that crosses can be performed in either direction.
With the increase of information about the biology of plants and other organisms, we can now see our way forward to realizing this scenario. For instance the structure and function of most of the genes involved in the critical decision to make a reduced egg cell have already been identified in yeast, a higher organism that is very simple to work with in laboratories. Many similar genes are being identified in plants.
Additionally, choice of the proper 'model' apomictic plant to analyze both at the molecular and cellular level, will have a major impact. Recently, there has been very substantial progress in Australia and New Zealand using the apomictic weed Hieracium (see box).
To maximize the benefits to the agricultural community, it is crucial to retain the ability to introgress (insert) numerous genetic combinations into the apomictic background. Without this ability, apomixis would be restricted to a limited set of cultivars. Introgression of new genes requires sexuality in the plant, and therefore the apomictic trait must be able to be switched off temporarily. This could be achieved using compounds that can be applied to induce or repress defined gene cassettes that have been engineered. Some promoter control systems of this type have been described, including a number by laboratories in the private sector using proprietary agrochemicals. However, improved systems need to be available to even the most resourcelimited of the plant improvement community.
Public domain: the way forward
The form that the development of apomixis takes will determine who will benefit from it. However, the increasing commoditization of agricultural production and the concomitant privatization and centralization of agricultural research instills legitimate fears that key methodology and opportunities will become restricted. This would be particularly tragic in the case of apomixis, which could have an important impact if it were broadly available to the agricultural research and production sectors. This is especially true in the less developed nations that are struggling with the problem of reconciling the desperate needs for environmental preservation, enhancement of agricultural production, and managing increasing populations. It is therefore imperative to move forward with research into apomixis in the public domain before it is too late.
Richard A. Jefferson (CAMBIA, Australia)
|Interview with Richard Jefferson, director of CAMBIA
Richard Jefferson, director of the Center for the Application of Molecular Biology to International Agriculture (CAMBIA) explains the organization's unorthodox view on the application of biotechnology.
Q. The word CAMBIA is an acronym and in Spanish means 'it
changes'. Is there special significance to this? Does it in some way reflect
your own thinking?
Q. CAMBIA's stated goal is to encourage us to look 'beyond
model systems' and put the power of modern science in the hands of farmers.
How does it plan to do this?
Understanding how things work can give us important short cuts if we are wise enough not to assume we have all the answers. For example, research has shown that in tropical legumes, including mung bean, common beans, soya beans etc. the nitrogen that is derived from the fixation of atmospheric nitrogen by symbiosis with rhizobia, is transported in the plant as a set of signature compounds (ureides), while the nitrogen absorbed from soil reserves or fertilizer is transported in other forms. Under laboratory conditions, we can measure these compounds, and their ratio shows the efficiency with which crop is fixing nitrogen a very important parameter for measuring the health of a plant. However, we really need to do this in the field, and cheaply, so that any farmer can then use methods of their choice (many of which we cannot even guess) to manipulate the system to improve the efficiency. For instance by changing management strategies, germplasm combinations, rotations, irrigation etc.. CAMBIA thinks we can do this by using molecular biology to genetically 'engineer' plants not to fix nitrogen better we are miles from this but rather to produce two enzymes that give vivid colours on the living plant whose levels are proportional to these compounds. By visualizing the colours, one could then be able to estimate this crucial ratio, and assess the efficacy of an empirically adjusted system! This is a tangible example of developing living 'bioindicators' or 'sentinels', through using molecular biology.
Q. Haven't farmers during the past millennia not been able to develop
their own bioindicating skills?
|Ongoing research towards molecular apomixis
A joint ORSTOMCIMMYT project in Mexico, led by Y.
Savidan, on the introgression of apomixis from Tripsacum into Maize
reportedly is nearing fruition, and should prove itself in the next few
W. Hanna and colleagues, at the US Department of Agriculture,
Georgia are making substantial progress on introgressing apomixis into
J. Miles and J. Tohme at CIAT, Colombia, have recently
made important progress in molecularly 'mapping'
a gene or gene complex associated with apomixis in the tropical apomictic
In New Zealand, R. Bicknell has pioneered the use of the
important model apomict, Hieracium. He developed the suite of tools
necessary to make Hieracium a laboratory system, including genetic
transformation, anther culture, tissue culture, transposon mutagenesis
and others. In a collaboration with A.M. Koltunow of the CSIRO,
Adelaide, strides are made in the molecular and cellular biology of autonomous
apospory the most promising mechanism.
Anna M. Koltunow
CAMBIA, Canberra, through its International Molecular
Apomixis Project (IMAP), in which many of the above mentioned researchers
participate, is in the process of securing funding to carry this work forward.
The Food and Agriculture Organization (FAO) will be working with
CAMBIA in bringing together the expertise in all fields necessary to analyse
possible outcomes and to shape future research, ownership and application.
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