BARD — USA/Israel
Sugar and Acid Homeostasis in Citrus Fruits
Citrus fruit quality standards have been determined empirically, depending on species and on the particular growing regions. In general, the TSS (total soluble solids) to total acidity (TA) ratio determines whether citrus fruit can be marketed. The TSS/TA ratio of the fruit varies among species, growing regions and regional standards, and will determine a range of physiological parameters that are important for fruit quality. Soluble sugars account for most of the TSS during harvest, and changes in their levels are associated with the development of some physiological disorders in the fruit, such as granulation. TA is determined almost solely by the citric acid content, which reaches levels of 1-5% by weight in many cultivated varieties. Higher citric acid content than desired often reduce fruit quality during harvest. On the other hand, with some new easy peeler varieties, the problem is often low acid content at maturity, resulting in a tasteless fruit, or “too sweet” fruit, if sugars are remarkably high. Reduced acid content is sometimes associated with increased levels of secondary metabolites which further reduce fruit taste quality. Therefore, acid and sugar homeostasis in the fruit is critical for the management of existing cultivars, the development of new cultivars, the improvement of pre- and post-harvest strategies and the control of fruit quality and disorders. During the previous program we have developed a significant proteomic database containing over 2500 proteins, some of them are induced towards fruit maturation in defined cellular compartments. In addition, we gained further knowledge on citrate metabolism, citrate mobilization and transport, and sugar homeostasis. During the course of the current research, we will employ these tools to attain a better understanding of the key biochemical determinants affecting acid and sugar homeostasis, and the biochemical and molecular characterization of fruit disorders related to fruit quality. More specifically, we will (1) complete citrus fruit proteome and metabolome and establish a citrus fruit functional database, (2) further characterize the control of fruit acidity by studying the regulation of key steps affecting citrate metabolism and transport across the tonoplast, (3) study the fate of citrate, and (4) characterize sugar homeostasis by studying its transport and accumulation in the vacuole of the juice sac cell.
Dr. Avi Sadka, Dept of Fruit Tree Sciences, Volcani Center, ARO, Bet Dagan 50250, Israel
National Science Foundation
Arabidopsis 2010: Abiotic stress combination: Bridging the gap between Arabidopsis stress research and agriculture
The proposed research is designed to make significant contributions to the goals of the 2010 program – to understand the networking and function of every gene in Arabidopsis. The specific focus of the proposal is on abiotic stress combinations and the genetic and metabolic networks that respond to stress combinations such as drought and heat, drought and salinity and salinity and heat. Abiotic stress is the primary cause of crop loss world-wide, with losses in the US estimated at 14-19 billion dollars each year. While abiotic stress is routinely studied in Arabidopsis by applying a single stress condition such as drought, salinity or heat, this type of analysis does not reflect the conditions that occur in the field where crop plants are subjected to a combination of different stresses. The central objective of the project is to identify novel genes, gene networks and metabolic pathways that specifically respond to a combination of two different abiotic stresses. The hypothesis to be tested is that dedicated genes, networks and pathways are activated in plants that are simultaneously exposed to two different stress conditions. This project is design to bring Arabidopsis into the front line of applied research on abiotic stress tolerance, and bridge the gap between stress studies conducted with Arabidopsis in the lab and the conditions that impact crops in the field. The two key “Broader Impacts” of the proposed research are: 1) Development and maintenance of a centralized website that will bring together agronomists, breeders and Arabidopsis molecular biologists (http://www.ag.unr.edu/Stress_Combination/). 2) Educational outreach for K-12 and multidisciplinary training to postdoctoral, graduate and undergraduates trainees. Both undergraduate and K-12 outreach and training activities will target the under privileged and under represented in Science. Historically, abiotic stress combinations, such as drought and heat, had the outmost devastating economical and sociological impacts on the US, with losses of 48.4 and 61.6 billion dollars in 1980 and 1988 respectively. The proposed project will pave the way for the development of crops with enhanced abiotic stress tolerance, contributing to ameliorate the consequences of future wheater disasters that are likely to increase in frequency due to anticipated climatic changes.
Professor Ron Mittler, Dept of Biochemistry & Molecular Biology, University of Nevada, Reno, NV 89557
Professor Karen A. Schlauch, Dept of Biochemistry & Molecular Biology, University of Nevada, Reno, NV 89557
Professor Vladimir Shulaev, Virginia Politech Institute, Blacksburg, VA 24060
Generation Challenge Program
Delayed Senescence and Drought Tolerance in Rice
Accelerated leaf senescence and abscission are associated with drought in nature as a means to decrease canopy size. In perennial plants, this strategy contributes to the survival and the completion of the plant life-cycle under drought. In contrast, this strategy reduces the yields of annual crops, with concomitant economical losses. We hypothesized that it is possible to enhance the tolerance of plants to water deficit by delaying the drought-induced leaf senescence and abscission during the stress episode. Our working hypothesis is that senescence is mainly due to a type of cell death program that could be activated in different plants during drought stress. Suppressing it could therefore enable plants to develop a vigorous acclimation response that would result in enhanced drought tolerance with less yield losses. Using tobacco plants expressing an isopentenyltransferase (IPT) gene under the control of a stress- and maturation-induced promoter (PSARK) we showed that delayed drought induced leaf senescence resulted in remarkable drought-tolerant phenotypes, as well as minimal yield loss when plants were watered with only 30% of the water used under controlled conditions. The general objective of this proposal is to identify genes with major roles in conferring drought tolerance in rice, and to generate drought-adapted and water-use efficient rice cultivars in different genetic backgrounds. The specific aims of this proposal are to: (1) test the efficacy of stress-induced cytokinin synthesis in conferring drought tolerance in upland and lowland rice varieties overexpressing IPT; These tests will include physiological, biochemical and molecular characterizations (growth, photosynthesis, nutrient assimilation, growth and yield components, etc.) under greenhouse and field conditions; (2) identify and characterize genes playing significant roles in the cytokinin-dependent acquired drought tolerance and factors affecting their activity; (3) use forward-, reverse-genetics and TILLING to assess and confirm the roles of the identified genes in drought tolerance in rice.
Abdelgabi M. Ismail, International Rice Research Institute, IRRI
Rachid Serraj, International Rice Research Institute, IRRI
The UC Discovery Grant and Arcadia Biosciences Inc.
Development of drought-tolerant crops
The proposed project is a collaborative effort between Arcadia Biosciences, Inc and the Department of Plant Sciences at UC Davis for the development of transgenic crop plants with enhanced drought tolerance and improved water use efficiency. California’s agricultural industry is facing three key limiting elements: 1) scarcity of water resources with its negative impact in productivity and crop yield; 2) new climate conditions, brought about the long-term effects of global warming, with the concomitant increased frequency of drought periods; 3) The increased dependence on water import from other states affecting the competitiveness of our agricultural production.
We identified a maturation-induced gene, SARK (senescence-activated-receptor-kinase), and demonstrated that the transcription of SARK was also drought stress-induced. We generated transgenic plants expressing an IPT (isopenthyltransferase, gene encoding an enzyme that catalyzes the rate-limiting step in cytokinin synthesis) under the control of the SARK promoter. Our working hypothesis was that the induction of cytokinin synthesis, driven by PSARK-IPT would inhibit the drought-induced senescence of crop plants, protecting the source/sink relationship under stress, conferring enhanced drought tolerance. Our preliminary work confirmed our assumptions and clearly demonstrated that tobacco transgenic plants expressing PSARK-IPT were able to tolerate extreme drought conditions. The transgenic plants not only survived an extreme drought stress, but also displayed an improved water use efficiency that allowed watering the plants with only 30% of the normal amount of water without significant yield penalties. Our results indicate the feasibility of producing drought tolerant crops able to tolerate drought conditions and able to grow under restricted water regimes without yield losses.
The general objectives of this proposal are: (i) To generate crop plants with enhanced drought tolerance and evaluate their growth, yield, fruit and grain quality under greenhouse and field conditions; and (ii) To enhance the drought-tolerance technology transfer process and accelerate the delivery and commercialization of drought tolerant crops.
The specific aims of this proposal are:
(1) To test the efficacy of stress-induced cytokinin synthesis in monocot (rice) and dicot (tomato, canola) plants in enhancing drought tolerance and water use efficiency under greenhouse conditions. These tests will include physiological (growth, photosynthesis, nutrient assimilation, yields, etc.) and biochemical (fruit, seed and grain quality) attributes.
(2) To evaluate the performance of transgenic drought tolerant plants under field conditions, and during irrigation with water-limiting regimes.
(3) To further characterize the cellular/molecular mechanisms associated with the enhanced drought tolerance transgenic plants expressing the PSARK-IPT gene, aimed at the identification of molecular determinants for an improved water use efficiency and drought tolerance in monocot and dicot crops. The discovery of these determinants will provide the basis of a broader platform of gene expression technology and intellectual property and accelerate the commercialization of the drought-tolerant technologies.
UAE Ministry of Presidential Affairs and UAE University
The production of stress tolerant trees
The United Arab Emirates is in constant need of stress-tolerant plants, trees and grasses for numerous urbanization and biotechnological programs. Tree species and turf grass varieties have been identified to show remarkable tolerance to water- and salt-stress, making them ideal for further stress-tolerance development and rendering them valuable assets in terms of a source for stress tolerant plants. Some of the species identified for the development of this project are Leptadenia pyrotechnica, Prosopis cineraria, Conocarpus erectus and Turf grasses. The project will entail the following phases: 1) Vector construction and cloning of the tolerance-genes to be transferred to the selected plant species; 2) Genetic transformation of plant embryos using Agrobacterium-mediated transformation; 3) Plant embryo proliferation and genetic selection of transformants; 4) Germination and propagation of selected plant embryos; 5) Evaluation of plant stress-tolerance using greenhouse-trials.
Professor A. Zaid
Chief Technical Adviser / Director
Date Palm Research & Development Programme
United Nations Office for Project Services – UNOPS
P.O.Box. 81908, Al Ain, United Arab Emirates