Location: Plant Physiology and Genetics Research2012 Annual Report
1a. Objectives (from AD-416):
Objective 1: Develop enhanced germplasm and cultivars for low input, high yielding, cost-competitive oilseed, latex, and biomass crops as bio-fuels and bio-based products. Objective 2: Determine the physiological, biochemical, and molecular factors limiting the growth and yield of oilseed, latex, and biomass crops that could be targeted for improvement in a conventiional and/or molecular breeding program. Objective 3: Develop economical production systems for new/alternative industrial crops.
1b. Approach (from AD-416):
Germplasm that has been previously collected as well as new germplasm collections will be evaluated for important characteristics to meet the objectives. Evaluation data and seed will be sent to the appropriate curators for entry into the National Plant Germplasm System. Standard and molecular breeding procedures will be used in selecting and improving germplasm to develop enhanced germplasm with increased levels of desired traits such as oil content, specific fatty acid profiles, latex and resin contents, yield, resistance to biotic and abiotic stresses, and biomass. Production systems will be developed and evaluated to provide farmers with profitable and sustainable management practices. New and improved analytical procedures will be developed as needed to evaluate germplasm for desired traits and potential co-producers.
3. Progress Report:
Work conducted in support of Sub-objective 1A was completed ahead of schedule and accomplishments included in last year’s annual report (2011). In support of Sub-objective 1B, two different transgenic lines of Lesquerella were constructed to alter seed oil content and composition for over-production of hydroxyl fatty acids and the synthesis of wax-esters containing hydroxyl fatty acids. While the specific transgenes used to generate these traits are somewhat different than the original targets described in the objective, both oil traits have potential usage as high performance lubricants and/or biofuels, which is the overall goal of the program. Stable inheritance of the transgenes for increased hydroxyl fatty acid production has been demonstrated, and plants carrying transgenes for wax synthesis are being regenerated from tissue culture and moved into soil. Recovery of seed is underway to determine the extent of oil modification. In support of Objective 2, a detailed transcriptome analysis has been performed on cold-acclimated guayule plants, providing insight to the changes in gene transcription that are associated with altered rubber production. Results demonstrated that (1) gene expression is not controlling the enzymatic activity of the rubber transferase complex, but instead post-translational modifications are the likely point of enzymatic control, or (2), proteins associated with the genes analyzed are not those regulating rubber biosynthesis, and thus critical member(s) of the rubber transferase complex are yet to be identified. The composition of this research group, in general, has changed significantly over the past few years including the departure of the principle scientist working on Lesquerella, the retirement of the principle scientist working on guayule, the reassignment of a scientist to another research project, and the hiring of a new scientist whose work is peripherally related to the existing research objectives. As such, in addition to conducting work towards the current goals of the program, the scientists have conducted additional work primarily in the area of oilseed improvement and abiotic stress response, which form the core of the next research project. ALARC has also recently been named as a regional Biomass Center, with an emphasis on utilization of oilseeds as feedstock for production of biofuels. Work conducted in this area in the past year included the completion of a two year study evaluating the performance of 16 camelina genotypes under high and low water treatments that showed differences among genotypes for maturity, yield, and response to water use. A second one year study evaluated the agronomic and phenotypic characteristics of 20 lines each of Brassica carinata, Brassica juncea, Brassica napus, Brassica nigra, and Brassica rapa under high and low water treatments that showed variability for many characteristics including flowering time, seed yield, biomass, and other characteristics. Additional work focused on elucidating genes involved in the synthesis of the plant cuticle, which is the outer most layer on the plant surface that forms a waxy, protective barrier involved in abiotic stress tolerance.
1. Production of biofuels in the leaves of plants. The demand for plant oils as feedstock for biofuel production is far greater than what agriculture can currently deliver, and novel methods for producing higher amounts of energy-dense oils in plants are needed. Plant oils are typically derived from seeds, but the biomass of a plant is dominated by leaves and stems. As such, production of even modest amounts of oil in plant leaves could significantly increase the total amount of energy recovered from crops. In collaboration with scientists at the University of North Texas and the University of Guelph, ARS scientists in Maricopa, AZ, have identified a two-protein system in plants cells that regulates the total amount of oil in plant leaves. Disruption of either gene in Arabidopsis resulted in a 10-fold increase in oil content, providing proof of concept that oil content can be dramatically increased in leaves. These results provide new insight to molecular targets that might be manipulated to increase the total amount of oil, and thus bioenergy, that can be recovered from crop plants.
2. Characterization of genes involved in rubber production in guayule. Guayule is a woody desert shrub under development as a domestic source of natural rubber for cultivation on semi-arid farmlands. Genetic modification of guayule for increased rubber yields could significantly contribute to economic sustainability of this new crop, but until now little information has been available on the genetic makeup of the plant. ARS scientists in Maricopa, AZ, performed a comprehensive analysis of guayule gene expression in bark tissues from winter grown plants, a time period when guayule is actively accumulating rubber in the bark. Surprisingly, expression of genes thought to be associated with rubber synthesis did not generally correlate with increased rubber synthesis activity, strongly suggesting that other factors than gene expression are important in regulating rubber production. A better understanding of the biochemical and genetic control of rubber production may lead to more success in breeding or genetic engineering of increased rubber yield.
3. Identification of genes controlling cuticle formation. The plant cuticle is under genetic control, and is a major determinant of crop drought stress tolerance. ARS scientists in Maricopa, AZ, identified sequences of two new genes controlling cuticle metabolism, and whose products also regulate whole plant transpiration rates, and plant water conservation. Information generated in these studies sheds light on the cellular function of genes involved in cuticle synthesis, as well and the role of physico-chemical properties of the cuticle as a barrier to water loss. These genes have excellent potential to be used in crop improvement to breed for more drought tolerant crops, and work is now underway to test this potential in the important oilseed Camelina.
4. Methods for improving post-harvest quality of peppers. Postharvest water loss from fruits and vegetables causes major financial losses to the fruit and vegetable industries. ARS scientists in Maricopa, AZ, in collaboration with Israeli scientists at the Volcani Center in Israel, employed a biochemical-genetic strategy to identify major chemical factors influencing the permeability of pepper (Capsicum sp) fruit cuticle to water. These studies revealed that cuticle composition, rather than cuticle thickness or structure, plays the major role in fruit water loss. Specifically, the ratios of alkanes to triterpenoids plus sterols in the waxes had a major impact on fruit water loss, with higher alkanes in the cuticular waxes associated with fruits having lower water loss rates. Breeding programs are now taking these findings into account when breeding for new cultivars, and searching for QTL markers linked to these traits.
5. Identification of wheat varieties for breeding abiotic stress tolerance. Breeding programs for crops grown in developing countries, such as Pakistan, are not advanced. To help accelerate the breeding process in wheat, an ARS scientist in Maricopa, AZ, collaborated with two scientists in Pakistan to assess a variety of wheat genotypes for water stress and chilling responses. The results of these studies revealed that heading time and grain yield of the spring type wheat cultivars examined is affected by chilling treatments, with recommendations that cultivars GA-02, Inqilab-91, Chakwal-50 and Fareed-06 be sown in mid-December, while Sehar-06 be sown in the start of January, in Pakistan to meet their chilling requirement under field conditions without substantial yield reduction. Findings from these studies shed much light on the kinds of varieties that may perform well in arid zones, and are useful in guiding the selection of parents to be used in new breeding programs.Ponciano, G.P., Mcmahan, C.M., Wengshuang, X., Lazo, G.R., Coffelt, T.A., Collins-Silva, J., Nural-Taban, A., Golley, M., Shintani, D.K., Whalen, M.C. (2012). Transcriptome and gene expression analysis in cold-acclimated guayule (Parthenium argentatum)rubber-producing tissue. Phytochemistry. 79:57-66.