1a. Objectives (from AD-416):
Objective 1: Define the key regulatory elements controlling photosynthate partitioning and nitrate assimilation and their interactions; develop and begin to test strategies to modify those processes for agricultural purposes. Objective 2: Determine the mechanistic basis for limitations on photosynthetic performance including those imposed by agriculturally significant stresses. Objective 3: Establish the major features controlling the response of photosynthetic productivity in soybean and corn to elevated atmospheric CO2, tropospheric ozone, and their interactions with drought and temperature, explore the bases for genetic variability in responses, and test potential transgenic amelioration strategies. Objective 4: Determine the environmental impacts of land cover change associated with alternative bioenergy crops.
1b. Approach (from AD-416):
Investigate isoform specificity for nitrate reductase (NR) posttranslational modification in vivo, and elucidate the impact of 14-3-3 binding on NR protein degradation. Localize the membrane binding site(s) on sucrose synthase and identify factors that may control the interaction. Use high-resolution spatial and temporal analysis of leaf growth to identify specific areas where leaf growth is occurring. Determine the biochemical factors responsible for the lower activation state of Rubisco, at high temperatures and test potential transgenic amelioration strategies. Further elucidate the role of Rubisco activase in thermal sensitivity/tolerance. Determine the biochemical basis for the "Green Seed Problem" of canola. Perform metabolite analysis of growing leaves under elevated CO2 and O3 to identify key components that may be involved in controlling growth. Determine the factors that lower the activation state of Rubisco under sink- and/or N-limited conditions, which are often encountered when plants are grown under high CO2. Explore the interaction of elevated CO2 with drought on soybean performance. Explore the interaction of elevated CO2 with temperature on soybean and corn performance. Determine if growth at elevated CO2 enhances or ameliorates oxidative stress. Determine the impact of land cover change from row crops to perennial grasses on hydrological cycle and carbon biosequestration.
3. Progress Report:
Experiments are underway to investigate the impact of leaf chlorophyll content on light energy distribution within soybean canopies and its impact on the daily integral of carbon gain at progressive developmental stages. We are testing the hypothesis that due to too much chlorophyll the top of crop canopies photosynthesis is over light saturated while lower levels of canopy are light starved. We are conducting a full suite of light absorption, reflectance and transmission measurements as well as photosynthesis and agronomic measurements.
1. Redefined the ozone dose response of modern soybean lines. ARS scientists evaluated the relationships between physiological parameters and their time courses of response to ozone and identified and characterized an exposure response/threshold for soybean under fully open-air agricultural conditions at the SoyFACE research site in Urbana, Illinois. On average, soybean yields are reduced by ~35 kg ha-1 per ppb of ozone over ambient concentrations. There is a linear decline in canopy area, photosynthetic capacity and harvest index in increasing ozone concentrations, which together accumulate to reduce yields. Water use efficiency of the soybean also decreased with increasing ozone concentration, suggesting that selection for more water use efficient lines may be a strategy to dealing with ozone pollution. The study also provides strong evidence that modern soybean lines are not more ozone tolerant than older lines, so breeders have not fortuitously bred for ozone tolerance. This shows that only through direct selection can the natural ozone tolerance that exists in soybean be selected for in commercial cultivars.
2. Reveal important gaps in understanding of crop responses to elevated carbon dioxide (CO2) in temperate versus tropical growing regions. ARS researcher in collaboration with University of Illinois at Urbana-Champaign collaborators defined the geographic and environmental distribution of elevated CO2 experiments on crop and native plants. Experimental data on plant and crop responses to elevated [CO2] are vastly more prevalent for economically and ecologically important systems in the temperate zone. There is a critical lack of experimental data that is most severe in the tropics and subtropics, but also includes high latitudes. Physiological understanding of the environmental conditions and species found at high and low latitudes suggest they may respond differently to elevated [CO2] than well-studied temperate systems. This work identifies a priority area for research as predicting the impacts of elevated CO2 particularly in the tropics is critical to accuracy of predictions of global food security later in the century.
3. Calcium-dependent protein kinases have tyrosine phosphorylation activity. Calcium is a central molecule in the transmission of information in plant cells and is involved in the coordination of key aspects of plant growth and development. One important mechanism in mediating calcium transmission of cellular information involves the regulation of the phosphorylation of specific plant proteins especially a large family of proteins known as calcium-dependent protein kinases (CDPKs). The CDPKs are long-known to be able to put phosphate molecules on the specific amino acids serine and threonine residues. However, in the work by ARS scientist, several of these CDPKs were demonstrated to act on tyrosine amino acids as well. These results indicate that at least some of the tyrosine phosphorylation may be catalyzed by a well-known family of protein kinases that are regulated by calcium. Identifying specific sites of autophosphorylation provides new targets for changing the response of plants to environmental conditions such as drought.
4. Water use of soybean decreases with rising ozone. The impact of growth at elevated tropospheric ozone on soybean water use was investigated over five growing seasons. The years with the highest ozone concentrations resulted in the largest decline in water use. This, in turn, increases the canopy temperature and, as ozone concentrations continue to rise, might result in ground-level heating beyond what general circulation models are predicting for future environmental conditions. This work illustrates sources of global warming which are direct caused by fossil fuel burning but not resulting from the green house gas warming.
5. Newer bioenergy crops are sinks for carbon during crop establishment. The primary goal of bioenergy feedstocks are to offset the usage of fossil fuels and atmospheric CO2 and other pollutants that accompany their use. A possible consequence of altering land use from existing row crops such as corn to newer generation bioenergy crops (e.g., perennial grasses) is that the process of converting the land might drive excessive amount of carbon from soils into the atmosphere, negating short-term benefits of the harvested feedstocks. The results from this research show that even during the transition phase of establishing perennial grasses, these ecosystems take up rather than release CO2. Thus, the secondary benefits of capturing atmospheric CO2 associated with these ecosystems in the Midwestern U.S. are realized early.
6. Impact of ozone on net primary production and implications for climate change. ARS scientists in collaboration with scientists in the United Kingdom reviewed the atmospheric chemistry governing tropospheric ozone mass balance, the effects of ozone on crop productivity, and implications for agriculture, carbon sequestration, and climate change. This work identifies the current impact of ozone on agricultural and natural ecosystems and examines how crop responses of plants may affect future atmospheric conditions. Information from this analysis was used for the 2012 National Climate Assessment, a large multidisciplinary project that summarizes the current state of scientific understanding of the impacts of changing climate.
Clouse, S.D., Goshe, M.B., Huber, S.C. 2012. Phosphorylation and RLK signaling. In: Kemmerling, B., Tax, F., editors. Receptor-Like Kinases in Plants: From Signaling to Development. Berlin Heidelberg, Germany: Springer-Verlag. p. 222-252.