Location: Plant Physiology and Genetics Research2011 Annual Report
1a. Objectives (from AD-416)
Objective 1: Improve crop stress tolerance by determining, and developing technology to ameliorate, metabolic limitations by biological processes most sensitive to abiotic stress factors common in arid southwestern U.S. cropping systems. [NP 301, C4, PS 4A] Sub-objective 1a: Improve crop tolerance to heat stress by devising approaches to improve the ability of Rubisco activase to activate Rubisco at leaf temperatures above the optimum for photosynthesis. Sub-objective 1b: Develop new approaches to improve chilling tolerance by identifying metabolic mechanisms that limit biochemical/physiological processes most sensitive to chilling temperatures. Objective 2: Develop improved germplasm resources for abiotic stress resistance and fiber quality in Gossypium barbadense and G. hirsutum utilizing and integrating classical and biotechnology-based methodologies. [NP 301, C3, PS 3C] Sub-objective 2a: Develop improved germplasm resources for abiotic stress resistance and fiber quality in G. hirsutum utilizing and integrating classical and biotechnology-based methodologies. Sub-objective 2b: Develop improved germplasm resources for abiotic stress resistance and fiber quality in G. barbadense utilizing and integrating classical and biotechnology-based methodologies.
1b. Approach (from AD-416)
The genetic potential of cotton, and crop species in general, for producing of abundant high quality economic yield is severely compromised by specific abiotic stresses, like supra-optimal temperature and water deficiency, that are endemic to the arid-southwestern U.S. In addition, early season chilling stress impacts yield by stunting growth and delaying planting date. The negative impact of these stresses is likely to intensify as the global climate changes and water availability becomes more limiting. The mission of this research unit is to use a multidisciplinary approach to improve stress tolerance and yield in cotton. Fundamental approaches that integrate physiology, biochemistry, biotechnology and classical plant breeding will be used to identify and modify the response of cotton to environmental stress. Through this research, new sources of cotton germplasm will be developed with improved stress tolerance, as well as higher fiber quality and enhanced yield. The basic biochemical strategies developed for improving stress tolerance in cotton will have broad application to the variety of crop plants cultivated in arid environments.
3. Progress Report
This report documents progress for Project Number 5347-21000-011-00D, which started in April 2010 and continues research from Project Number 5347-21000-009-00D, entitled “Physiological and genetic basis of cotton acclimation to abiotic stress.” Progress on this project focuses on Problem 3C, the need for enhanced germplasm and improved crops that are tolerant to abiotic stresses and have superior agronomic characteristics, and Problem 4A, the need for leveraging knowledge of fundamental biological processes in model plant systems to enhance crop productivity. Under Sub-objective 1B, we made significant progress in identifying omega-3 fatty acid desaturase genes present in cotton. Two different types of omega-3 fatty acid desaturase are known to exist in plants, and we found three genes of the first type, and two genes of the second type. Full length DNA fragments have been obtained for three of the genes, and partial DNA fragments have been recovered for the other two. The recent release of a draft genome sequence from Gossypium ramondii will significantly accelerate the recovery of the remaining DNA sequences for these genes. Under Sub-objective 2A, methods of cotton transformation were developed and refined, resulting in an efficient procedure for producing transgenic cotton plants. A variety of lipid modifying genes, including an omega-3 desaturase, have been introduced into cotton to determine whether over-expression of omega-3 desaturases in cotton leaves will increase their chilling tolerance. First generation transgenic plants have been confirmed, and cotton plants are currently flowering and will soon produce seed (which will allow us to determine whether the transgenes have been stably inherited). Under Sub-objective 2B, we made significant progress in understanding the biological mechanisms responsible for the tolerance and sensitivity of Pima cotton to heat and drought stress. With the implementation of biochemical, physiological, and proximal remote sensing tools, we showed that canopy temperature is predictive of tolerance to high temperature and water deficit. To enable this research on a large scale, infrared thermometers were attached to a high clearance tractor. This allowed high-throughput monitoring of thousands of Pima cotton plants over the course of a growing season. In addition, our biochemical investigations showed that a decrease in Rubisco activation in Pima cotton occurred under a combined heat and drought stress, accounting for a significant non-stomatal limitation to photosynthesis.
1. Characterization of proteins that regulate photosynthesis. Two important enzymes that are involved in the process of photosynthesis are turned off and on by a small protein called CP12. To determine if CP12 also controls some of the other enzymes of photosynthesis, ARS scientists in Maricopa, AZ purified a complex containing CP12 for the first time from tobacco and the model plant, Arabidopsis. Chemical analysis showed that the purified complex contained CP12 and the two photosynthetic enzymes, but no other enzymes. The results indicate that CP12 plays a specific role in controlling the two photosynthetic enzymes in response to light. Since the rate of photosynthesis changes in response to light and other environmental conditions, this information could be used to optimize the photosynthetic performance of plants to maximize yield and as such farmer profit in environments that are prone to high temperatures and limited rainfall.
2. Omega-3 fatty acid desaturases are regulated by changes in temperature. Many crop species are sensitive to cold temperatures, and chilling damage can cause significant losses for agricultural producers. Plants generally respond to colder temperatures by increasing the amount of protective omega-3 fatty acids in their cellular membranes, but the mechanism(s) involved in inducing this change are not well understood. ARS researchers in Maricopa, in collaboration with scientists at the University of Guelph and the University of North Texas, have elucidated key aspects of this regulatory process by identifying specific amino acids within omega-3 fatty acid desaturases (the enzymes responsible for omega-3 fatty acid production) that are involved in temperature-dependent regulation, as well as several additional proteins in plant cells that are involved in regulating enzyme activity. This information opens new avenues of research for examining temperature adaptation in plants and may speed the development of plant cultivars that have increased cold tolerance.
Khuu, N., Gidda, S., Shockey, J.M., Dyer, J.M., Mullen, R.T., 2011. The N termini of Brassica and tung omega-3 fatty acid desaturases mediate proteasome-dependent protein degradation in plant cells. Plant Signaling and Behavior. 6(3):422-425.