Drs. Schroeder and Takahashi of UC San Diego have discovered and characterized a stomatal CO2 sensor and the underlying mechanism in plants. This unique plant CO2 sensor shows very strong phenotypes in mutants, with complete lack of a CO2 response. Moreover, the researchers can reconstitute this CO2 sensor with the recombinant protein complex in vitro. They are using this discovery to further develop genetic applications to modify CO2 sensing and water use efficiency in plants. The researchers have identified two protein kinases, which regulate a Raf-like protein kinase which in turn controls another Raf-like kinase activity in response to change in CO2/bicarbonate concentration in vitro. Mutants in each of these proteins completely disrupt CO2 responses in plants, consistent with our CO2 sensor findings. Biochemical structure analyses reveal important phosphorylation sites and provide insight into the direct CO2 sensing and signaling core mechanism in plant cells.

The response of plants to reduced water availability is controlled by a complex osmotic stress and abscisic acid (ABA)-dependent signal transduction network. The core ABA signaling components are snf1-related protein kinase2s (SnRK2s) which are activated by ABA-dependent inhibition of type 2C protein phosphatases and by an unknown ABA-independent osmotic stress signaling pathway. Limited water availability is one of the key factors that negatively impacts crop yields. The plant hormone abscisic acid (ABA) and the signal transduction network it activates, enhance plant drought tolerance through stomatal closure, and inhibition of seed germination and growth. As plants are constantly exposed to changing water conditions, reversibility and robustness of the ABA signal transduction cascade is important for plants to balance growth and drought stress resistance. Core ABA signaling components have been established the ABA receptors PYRABACTIN RESISTANCE (PYR/PYL) or REGULATORY COMPONENT OF ABA RECEPTOR (RCAR) inhibit type 2C protein phosphatases (PP2Cs) resulting in the activation of the SnRK2 protein kinases SnRK2.2, 2.3 and OST1/SnRK2.6 . However, it has remained unclear whether direct autophosphorylation or trans-phosphorylation by unknown protein kinases re-activates these SnRK2 protein kinases in response to stress. The osmotic stress sensing mechanism and upstream signal transduction mechanisms leading to SnRK2 activation remain largely unknown in plants.

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Inorganic nitrogen is a vital nutrient for plants. Soil nitrate provides as much as 90 percent of the nitrogen taken up by most plants and leads to a dramatic change in gene expression, which is critical to direct the productivity and survival of the plant. Consequently, nitrate is commonly provided by way of fertilizer to improve crop yield. However, many crop plants are inefficient in their ability to utilize the nitrogen. For example, corn and wheat typically only utilize 50 percent of the nitrogen applied to the soil and paddy rice may recoup as little as 30 percent. Nitrogen not used by crops may contribute to severe environmental problems, including pollution of ground water, run-off into nearby bodies of water, and release of greenhouse gases into the atmosphere. Plants take up and assimilate nitrate in response to its availability in the soil and the demands of the plant, but with varying efficiency among species. Understanding and improving the ability of particular plant species to respond to and utilize nitrogen could therefore lead to increased crop productivity and decreased water and air pollution.

In many agricultural seed products—such as oilseed crops, grains, and legumes, as well as seed for planting—the premature release of seeds prior to harvest results in serious losses. Prior to this invention, visual examination of the crops and other agricultural techniques, such as determination of moisture content, have been the primary means to indicate timing of the seed harvest. This invention uses antisense genetic manipulation to achieve rational control of the natural regulatory mechanism of seed release.

Full realization of the potential of many transgenes depends on selective expression in tissues of interest. The following describes a plant promoter isolated from Arabidopsis thaliana that is operative only in the dehiscence zone tissues of plants, and is suitable for driving the expression of genes desired to operate only in this tissue.

In many agricultural seed products—such as oilseed crops, grains and legumes, and seeds harvested specifically for planting—premature release of seeds prior to harvest results in serious losses. Swathing and other methods for minimizing harvest loses add to overall production costs. In addition, regardless of cost factors, the need for positive control of seed release may in future years become a desirable capability when genetically modified organism (GMO) crops become widespread, in order to assure satisfactory containment.

Oil seed crops, such as canola (Brassica), often break their seed-pods prematurely. This premature seed release can be a result of harvesting techniques or adverse weather conditions. Premature release can cause from 10 to 50 percent crop loss in canola, using current harvesting techniques.

It is currently unknown how plants sense the level of CO2 in the atmosphere. Previously, no CO2 sensors have been identified in plants. Knowledge of how atmospheric CO2 is perceived could be used to manipulate plant CO2 responses so that the carbon and water use efficiency during plant growth could be optimized. The water use efficiency defines how well a plant can balance the loss of water through stomata with the net CO2 uptake for photosynthesis, and hence biomass accumulation.