|
Introduction
National Program 302 Plant Biological and Molecular Processes houses much of the agency's fundamental crop research that is necessary for practical advances but is too far upstream to provide solutions directly for practical problems. The research focuses on mechanistic understanding of specific plant processes and properties, so that the knowledge and tools developed can be used to improve functions and properties of plants. The program is divided into three components: Analysis and Modification of Plant Genomes (functional genomics, focusing on the molecular end of the spectrum; and technology for modifying plant genomes); Biological Processes That Determine Plant Productivity and Quality (plant growth and development, photosynthesis, productivity, and environmental responses relating processes and attributes of the whole organism to their genetic and metabolic underpinnings and providing the context for molecular manipulations); and Mechanisms of Plant Interactions With Other Organisms (plant defense reactions to pests and pathogens, emphasizing those that reduce the need for applied pesticides; interactions with beneficial organisms; and secondary metabolism and products). Together, these research approaches provide a continuum of understanding from genes to phenotype (plant attributes and performance). During 1999, there were many important discoveries and advances. Some of them are described below, grouped by program component.
A workshop was held June 21-23, 1999, involving ARS scientists from this National Program and a diverse array of customers, stakeholders, and partners. The workshop provided an opportunity for ARS stakeholders to communicate their future needs and concerns. Following the workshop, an ARS team of scientists wrote a draft action plan that identifies broad areas for research to address those needs and concerns. The draft action plan was posted on this website in mid-November 1999, for comments. A revised plan, incorporating the feedback received, is expected to be posted by January 2000. From that plan, research project plans will be written and peer reviewed during the year.
Selected Accomplishments for Fiscal Year 1998 (Listed by Component)
Analysis and Modification of Plant Genomes
With today's rapid developments in genetics and genomics, many possibilities for improving plants exist now that were unimaginable even a few years ago. Barriers to movement of single genes or small numbers of genes across unrelated species are being breached, allowing transfer of key genetic capabilities not just among higher plants but across classes of organisms (such as from bacteria to plants). New information about DNA structure provides insights into how gene activities are regulated and coordinated with other related genes. Soon, there may be means to direct rearrangements of DNA by the plant's internal mechanisms, without introducing any new genes. As part of a broad approach to improving plant performance, the research in this component of the program develops an understanding of the molecular mechanisms underlying plant functions.
More efficient production of transgenic cotton plants . Genetically engineered insect-resistant cotton plants have been highly successful in reducing pesticide use. More commercial success stories would be possible if the procedure for engineering the plants were simpler and less expensive. A major obstacle has been the difficulty of regrowing intact plants from genetically transformed cells. ARS scientists at New Orleans, Louisiana, have identified a genetic marker that indicates when embryo (plantlet) formation occurs in cotton. This marker will enable much quicker identification of embryo formation and will lead to more efficient and less laborious techniques to make genetically engineered cottons.
Wheat transformed with only a single copy of a foreign gene. The production of transgenic crop plants is becoming more important in agricultural biotechnology. For commercial success, it will be necessary that traits introduced be transmitted faithfully through successive generations in a predictable manner. Genetic transformation of plants often results in multiple copies of the introduced DNA at a single locus, and multiple-copy insertion sometimes results in transgenes inactivation, sometimes called gene silencing. To ensure that only a single copy of a foreign gene resided in a plant genome, ARS scientists at Albany, California, used a strategy based on site-specific recombination. They used wheat to demonstrate the success of this strategy.
Risk of gene flow between cultivated sunflowers and wild prairie sunflowers assessed . The gene flow between a wild prairie sunflower and cultivated sunflowers is of concern for future transgenic sunflower research. ARS scientists at Fargo, North Dakota, estimated introgression and hybridization between the prairie sunflower and cultivated sunflowers by using selectable molecular markers. They found the frequency of gene exchange was low, averaging 1.4 percent. While this research demonstrates that there would be less of a concern because of the low frequency of the gene flow, there still is potential for transgenes to enter into wild prairie populations.
Biological Processes That Determine Plant Productivity and Quality
Crop plants do not use or inefficiently use all of the resources available to them. In many cases, the governing traits involve the growth and development of the intact organism. In this program component, research is focused on the complex processes of plant growth and development, productivity, and efficiency, and how they are related to gene action and metabolism. The responses of these processes to environment, especially stressful (nonoptimal) environments, are especially important because environmental limitations to efficiency are the major reason for poor and variable yields. Research conducted under this component of the program identifies specific genes or gene products that control plant functions, allowing improvement efforts to be focused on the appropriate targets.
A gene to block preharvest sprouting of wheat grains . In the Pacific Northwest, preharvest sprouting of wheat grains after a rain can ruin the crop. ARS scientists at Pullman, Washington, in cooperation with others, have identified a gene in dormant wheat that prevents the sprouting and demonstrated that the gene, when engineered to be expressed in sprouting-susceptible plants, is effective in blocking the sprouting process. This gene represents a new method to prevent sprouting and protect end product quality.
Reducing chilling sensitivity of tropical fruit trees . Chilling sensitivity of tropical and subtropical fruits, such as mango, severely limit their production in the United States. Collaborative research between ARS scientists at Urbana, Illinois, and an Israeli scientist has shown that chilling injury of mango requires a cold night followed by bright sunshine. The results suggest new strategies to limit damage by use of shades to reduce light intensity and could lead to northward expansion of production zones of tropical fruit.
Plant lignification is plastic. An important characteristic of plants as they mature is accumulation of lignin, an indigestible compound composed of phenolic components, found especially in stems. Although this adds to the ability of mature plants to stand upright, it reduces the digestibility of the cell walls and is a major reason for the low digestibility of forages when fed to livestock. A multidisciplinary team of ARS scientists at Madison, Wisconsin, who are seeking to manipulate lignin to improve the digestibility of forages, has gained insight into the biochemical processes of lignification. They found that the process is quite plastic, enabling mutant plants to use a wide variety of phenolic components to produce a functional lignin, some of which are less restrictive to cell wall digestion than others. This information creates a knowledge base for designing forage plants with improved digestibility.
Novel film-forming materials provide frost protection. Freeze damage to fruit and nut trees often results in a significant loss in yield, quality, or tree longevity. Using infrared thermography to study ice nucleation in plants, ARS scientists at the Appalachian Fruit Research Laboratory, Kearneysville, West Virginia, are developing novel film-forming materials to block ice nucleation and hence provide frost protection. Various formulations are being tested for application in field tests. A patent application for the use of this technology has been submitted. It is expected that this new approach to frost protection will be available to growers in 2 years.
Genetic control for corn metabolism elucidated. The genetic control for many important agronomic traits in crops is not well understood, which impedes progress in crop improvement. ARS scientists at Columbia, Missouri, combined analytical chemistry with leading-edge genetic analyses to clarify the role that the interactions between various genes play in controlling biochemical pathways. These results may help researchers and crop breeders who are trying to genetically engineer crop metabolic pathways by targeting the specific genes that must be altered to increase yields.
Soil amendments provide new opportunities for blueberry production. Highbush blueberries require an acid, well-drained soil with high organic matter content for maximum growth and fruit yield, but such soils do not exist in many places where it is desirable to grow this crop. At the Beltsville Agricultural Research Center's Fruit Laboratory, Beltsville, Maryland, growth and yield of blueberries grown in a coal ash compost mixture derived from municipal and industrial by-products was compared to production in soil used for commercial plantings in New Jersey. Popular blueberry varieties grew as well and yielded as much fruit in two coal ash-compost mixtures as plants grown in conventional production soils, thus providing a potential new sustainable production scheme for growers in regions where blueberry production has not been previously possible.
Transgenic corn for optimal swine feeding. Swine are fed a substantial proportion of the U. S. corn crop, but also require nutrient supplements for an optimal diet. ARS scientists at Ames, Iowa, produced transgenic corn with genes for a key protein in sows' milk and another protein with potent antibiotic properties. These results may enable production of corn that is nutritionally superior for swine feeding and, because of its antibiotic properties, might eliminate the need for extensive doses of tetracycline antibiotics. As a result, swine production might be more cost-efficient.
Potatoes show increased resistance to bruising. Blackspot of potato, caused by bruising, often reduces quality and value of both fresh market and processed potatoes. Blackspot arises from the physical damage in the tuber flesh that results in the accumulation of melanin pigment. ARS scientists in Prosser, Washington, have identified natural bruise resistance in a wild Mexican species Solanum hjertingii. Bruise suppression in this species results from a strong suppression of dark pigment formation. Crosses between S. hjertingii and cultivated potato showed complete suppression of bruise injury in the progeny. It may now be possible to control blackspot in traditional breeding programs.
Mechanisms of Plant Interactions With Other Organisms
Much of plant metabolism produces proteins or other compounds with a role in defense against pathogens or predators, as attractants for pollinators, or the like. In nature, these processes are as essential to plant health and survival as are the primary processes of photosynthesis and respiration. In many respects, they present the most attractive opportunities for crop improvement because they offer means to protect crops; to enhance nutritional balance, flavor, or other attributes of quality; or to promote important symbioses between crop plants and other organisms. Importantly, opportunities to enhance these processes may often be generated by focusing on a single gene or few genes, unlike the polygenic traits related to plant development, adaptation, and yield. Research will develop knowledge of relationships among host plants, pests and pathogens, and beneficial organisms, and of the specific molecular, biochemical, and physiological events that underlie those relationships. Most of this work will be targeted to specific identified needs, such as resistance to an identified pest or enhancement of a specific phytonutrient, and the knowledge will be intended to lead to new technology to satisfy those needs.
Corn that resists aflatoxin formation in the midsouth. Aflatoxin, caused by the fungus Aspergillus flavus, is toxic to livestock and causes cancer in humans. Contamination of corn grown in Texas and the Mid-South during 1998 by aflatoxin rendered much of the product unfit for interstate shipment and human and livestock consumption. ARS scientists at Mississippi State, Mississippi, have developed and released corn germplasm resistant to aflatoxin production. Cooperative agreements with Pioneer Hi-Bred International, Inc. and DeKalb have been implemented to evaluate corn hybrids for resistance to aflatoxin accumulation and desirable agronomic traits. ARS scientists at Mississippi State and New Orleans, Louisiana are working to identify corn genes that lower toxin in the seed. ARS scientists at Mississippi State released Mp715, a new corn germplasm line with the highest level of resistance to aflatoxin currently available. ARS scientists in New Orleans discovered two new proteins in resistant corn plants that ward off colonization of the corn plant by the fungus. These proteins could serve as biochemical markers to identify resistant plants.
Biocontrol agents and natural products reduce postharvest disease of fruits. Postharvest losses due to decay of fruits during storage, shipping, marketing, and home consumption are significant and represent a financial burden to both growers and consumers. At the Appalachian Fruit Research Laboratory, Kearneysville, West Virginia, new agents to reduce postharvest disease are being developed by using combinations of pathogen antagonists and by combining biocontrol agents with natural compounds and other additives. ARS scientists have identified beneficial bacteria, heat treatments, calcium infiltration regimes, and bioactive coatings that alone or in combination successfully control blue mold decay of apple and other decay pathogens and prevent growth of the foodborne pathogen E. coli 0157:H7. These new methods to control postharvest disease provide safer control alternatives and address safety, environmental concerns, and pathogen populations that are resistant to chemical.
Identifying ways to manage nematodes on cotton. Reniform nematodes are a rapidly increasing problem on cotton in the Mississippi Delta region. The possible causes of this increase in nematodes are not understood. ARS scientists at Stoneville, Mississippi, have now shown that fertilization with potassium increases reniform nematode infestation of cotton. This is a new finding that will help scientists to develop crop management and rotation schemes to suppress reniform nematodes.
|
Printable version
Email this page
