Molecular, Cellular and Physiological Mechanisms Associated with Delayed Leaf Senescence Induced Drought Tolerance in Crop Plants.
Drought is the most important environmental factor limiting crops productivity worldwide (Boyer 1982). Water availability for agriculture is becoming limited alongside with a projected rise in food demand for the expanding world population. Therefore, developing novel cultivars with more efficient water-use and greater drought-resistance capacity is the most viable solution to ensure a sustainable agricultural production and alleviate threats to food security.
Senescence of older leaves is an important strategy, enabling the reallocation of nutrients stored in the sources (e.g., older leaves) to the sinks (e.g., young leaves and fruits/grain). Environmental conditions such as drought may accelerate leaf senescence, affecting leaf physiology, plant reproductive development, hormone levels, etc. The progression of leaf senescence appears to be regulated by changes in gene expression resulting in changes in plant growth regulators, increase in reactive oxygen species (ROS), and the expression of senescence associated genes (SAG). Accelerated leaf senescence in response to drought is an important adaptive survival value because it reduces the water demand at the whole plant level (i.e., drought avoidance). Recently, transgenic tobacco plants over expressing isopenthyltransferase (IPT; an enzyme that catalyses the rate limiting step in cytokinin synthesis) were shown to delayed senescence, which enable them to maintained high photosynthetic activity during drought episode (Rivero et al. 2007, 2009).
Our hypothesis is that if during a water-stress episode the leaf senescence could be delayed, the plants should be able to display enhanced drought-tolerance which results in reduced yield loss. The induction of cytokinin synthesis, driven by a maturation- and stress-induced promoter (PSARK-IPT) would inhibit the drought-induced senescence, without significantly altering the source/sink relationships and conferring enhanced drought tolerance. The overall goal of this study is generating crop-plants with enhanced drought-tolerance and characterizing the physiological, cellular and molecular mechanisms enabling the transgenic-plants drought tolerance. The specific aims of this proposal are to:
(i) Examine the efficacy of stress-induced cytokinin synthesis in monocot (rice and wheat) and dicot (tomato) plants on performances under drought conditions.
(ii) Characterize gene expression profiles of transgenic vs. wild type plants, grown under stress and non-stressed conditions.
(iii) Characterize the metabolite profile of the transgenic vs. wild-type plants and underline specific pathway(s) associated with the enhanced drought tolerance of transgenic plants expressing PSARK-IPT.