Selected Accomplishments for Fiscal Year 1998 (listed by Component)

Site-specific gene insertion. Current techniques of genetic engineering insert genes randomly into the genome of the receiving plants. The randomness leads to unpredictable gene effectiveness. New technology, though, is able to label sites on the plant’s DNA, and genes can then be inserted into a selected labeled site. This technology has now been successfully used on wheat to introduce a foreign gene onto a specific site. The procedure will be useful in putting a herbicide resistance gene into wheat in a position where it cannot be genetically transferred to jointed goatgrass (a serious weed pest that is genetically closely related to wheat). A patent application has been filed.

A regulatory gene from corn inhibits senescence. A gene isolated from corn meristems -- growing tips -- was shown to be a regulatory gene that controls the activity of other genes. This gene, named knotted1, has now been linked to blockage of cell senescence and to accumulation of the natural plant hormone, cytokinin, which is known to retard senescence. This is the first regulatory gene found to be connected to senescence. Although not initially targeted as such, this discovery opens a path to developing slow-senescing ('stay-green') crops with higher yield potential.

Understanding pollen-pistil interactions. When pollen lands on the surface of the pistil, or female floral part, it will not germinate and grow a pollen tube unless it is recognized as the right type of pollen. ARS scientists have identified receptor-like kinases (a specific class of enzyme) in pollen that are important for pollen tube growth. These kinases are being used to identify the sequence of events that lead to successful fertilization. Short-circuiting of the hybridization barriers between species will allow wider genetic crosses across species without resorting to genetic engineering. In turn, this ability will allow breeders to broaden the genetic base of crops much more effectively.

Controlling plant responses to light. Previous work identified a family of genes, the phytochrome genes, that govern plant responses to light such as shade avoidance, photoperiodism (flowering controlled by daylength), and more. Overexpressing one gene, phyA, suppresses the shade avoidance response. A protein has now been identified that interacts directly with phyA. The nature of the protein suggests that it in turn regulates the activity of target genes in the cell nucleus. This work has tremendous potential to modify almost all processes of plant development, such as flowering in photoperiod-sensitive plants, that are controlled by light. Phytochrome mediated events determine much of a plant's adaptation to the environment, and thus can be used to expand a crop's range, to change the way it is grown, or to improve the yield stability in variable weather conditions.

New system of gene regulation. A novel method of regulating gene expression, allowing human intervention to 'turn on' genes when desired, received a patent. One application of this system, known as the Technology Protection System, is to protect intellectual property rights of the owners of patented genes by preventing germination of second-generation seeds. It will also prevent the spread of genetically engineered traits from crops to closely related species of weeds that can interbreed with the crops. The patented technology is being licensed to the private sector. Other important applications, such as preventing floral development in forage crops to improve forage quality, are also feasible.

New gene promoters for monocot plants. Genetic resistance to pests is frequently inadequate in crop plants. As a result, pests and pathogens are commonly controlled via pesticide spray programs. Expression of novel genes in transgenic plants will provide alternative opportunities for pest management. Promoter elements isolated from sugarcane polyubiquitin genes were transformed into sugarcane and rice to produce stable transgenic cell lines with high levels of marker gene expression. This breakthrough in the development of these new promoters will improve our ability to transform monocotyledonous crop plants (grasses, cereals, and some others) and obtain reliable expression of introduced genes. The technology has been transferred to other scientists active in the development of resistance to nematodes and other plant pests.

Hyperaccumulation of heavy metals for improving contaminated soils. Plants that accumulate heavy metals are an ideal 'low-technology' way to clean up, or remediate, contaminated soils. ARS scientists have identified a gene in a heavy-metal-accumulating plant that is responsible for uptake of large quantities of cadmium and zinc. The gene product is also responsible for iron uptake and is induced to high levels of activity by an iron deficiency in the soil. This gene is likely to be the basis for producing new hyperaccumulating plants to be used in phytoremediation.

Novel type of drought resistance characterized. Desiccation-tolerant plants ('resurrection plants') are protected from damage by drying, even if dried almost completely. Proteins that protect cells from damage or that promote repair of damage (rehydrins) have been isolated, and the modes of action of two have been identified. One is a dehydrin -- previously known to protect seeds against damage during dehydration -- and the other is an antioxidant enzyme. Transgenic plants have been created expressing high levels of these gene products, and testing of drought tolerance is under way.

Tool for identifying heat tolerance in plants. Environmental stresses such as excessive heat are major limitations to crop productivity. Identifying genetic lines that may have heat tolerance is time-consuming and difficult because each line must be grown and tested under the right conditions. ARS scientists described a concept that defines the basis for heat tolerance and used this concept to develop a quick and simple test. The test involves chlorophyll accumulation in germinating seedlings. When used as a screening tool, the test efficiently identified differences in genetic heat tolerance that can be exploited in a conventional breeding program to improve crop heat tolerance.

Understanding the pathway from photosynthesis to harvest. Photosynthesis is the basis for plant productivity, but the products of photosynthesis must be rapidly moved from the leaves to the grain or other 'sink.' When photosynthesis is rapid, the rate of product movement can limit photosynthesis and therefore plant productivity. ARS scientists have identified a key rate-controlling protein involved in the transport process. Movement of sucrose (sugar) into sinks is controlled by the concentration of sucrose itself: when sucrose is high, the transport protein becomes less active. This is the first description of how sugar transport is regulated. The knowledge is a first step in learning how to improve transport processes.

The plant hormone auxin controls fruit ripening. Perishable products such as fresh-market tomatoes are subject to large losses during postharvest storage and handling. As a result, tomatoes are picked green and artificially ripened later with ethylene gas, a ripening trigger. ARS research showed a likely role for the natural plant hormone, auxin, as a counterbalance for ripening agents during the normal ripening process on the plant. Tomato plants were genetically engineered with a gene from corn to make them accumulate more of this naturally occurring hormone. In test systems, the modification substantially slows tomato spoilage and extends the useful life. This is a new approach to extending fruit life, which is expected to be useful for most fresh fruits without introducing any artificial chemicals.

Genetically engineered disease resistance in floral crops. Floral crops, particularly bulb crops, are sensitive to viral and fungal diseases. Methyl bromide is often used for disease control, but this agent may shortly be unavailable. ARS has developed procedures for genetically engineering disease resistance into cells of monocot bulb crops (Gladiolus, lilies, Ornithogalum) and regenerating resistant plants. In 1998, excellent gene promoters were identified that are non-proprietary (available for use by anyone). This removes an important barrier to improving these high-value crops by biotechnology. Gladiolus plants with genes for bean yellow mosaic virus resistance have been generated and are currently being tested.

Increased phytonutrient content of tomatoes. There is strong interest in improving the quality of fruits and vegetables in the American diet. Lycopene is a constituent of tomatoes and is an important phytonutrient that helps fight cancer. Transgenic tomatoes were created that accumulate high levels of natural compounds called polyamines during ripening, which resulted in a 2.5 fold increase in lycopene content of the fruit. This is a new approach to fruit quality and a new finding. The work is expected to form the basis for creating a more healthful and high-value tomato.

Production of medicinal compounds from plants. There are many high-value natural products from plants that have useful properties. Identifying these products and learning what they do is a prelude to actually utilizing them. ARS has been studying the anticancer compound, podophyllotoxin, and has developed a new inexpensive process for obtaining it from mayapple. A patent application on the discovery has been filed. ARS has also shown that the antimalarial agent, artemisinin, is present only in the glands of the plant Artemisia annua. This is an important step in learning how to extract and purify the material and also how to proceed to genetically modify its accumulation rate. In addition to the medicinal benefits from research on these natural products, the work is expected to provide high-value crops that will be particularly important to small farmers.

Transgenic plums exhibit resistance to plum pox virus. Stone fruits are susceptible to a number of virus diseases. There is little or no natural resistance to most of these viruses, which reduce production and shorten life spans of infected trees. New transgenic plums genetically engineered to contain a virus resistance gene were shown to be highly resistant to the plum pox virus. Resistance to this virus offers the potential to reduce losses to growers caused by plum pox virus and, at the consumer level, reduce retail costs.