Location: Plant Gene Expression Center2012 Annual Report
1a. Objectives (from AD-416):
Objective 1: Define the contribution of the circadian clock to plant osmotic and salt stress responses using Arabidopsis as an initial model system. Objective 2: Characterize the contribution of the circadian clock to transcriptional control networks in cereals, using Oryza sativa as a model. Sub-objective 2.A.: Define the circadian transcriptome of Oryza sativa. Sub-objective 2.B.: Identify cis-regulatory elements upstream of co-expressed circadian genes. Objective 3: Determine the function of maize photoperiodism genes identified as naturally occurring alleles in maize recombinant inbred lines. Objective 4: Assess the feasibility of high-throughput screening of maize seedlings or plants for circadian phenotypes as a prelude to screening large RIL populations for circadian quantitative trait loci (QTL).
1b. Approach (from AD-416):
Maize is an important crop as well as a model system for other cereals such as sorghum, barley, rice and wheat. Our long term goal is to identify and characterize the activity of maize genes involved in plant production including tolerance to stressful growth conditions and regulation of flowering time. Recent work in model systems demonstrates that the circadian regulation of physiological activities is required for optimal plant growth and for tuning of responses to environmental cues. A comprehensive understanding of the circadian system in cereals is lacking; therefore, this proposal seeks to define the maize circadian system and assess the circadian oscillator’s contribution to important agronomic traits. Known circadian mutants will be tested for their response to salt and osmotic stress. Genes under circadian regulation in cereals will be identified by expression profiling, and this information used to computationally predict regulatory DNA elements that contribute to circadian gene expression. Reverse genetic approaches will evaluate the role of candidate photoperiodism genes in determining the timing of maize flowering. Maize inbreds and recombinant inbred lines will be analyzed for natural variation in overt circadian rhythms. DNA sequences, genes, mutants, and inbred lines identified here provide two types of tools: a better understanding of fundamental processes in environmental responses and targets that can be used to improve crop productivity.
3. Progress Report:
Progress was made under all objectives. Under objective 1, existing Arabidopsis circadian mutants were found to lack strong changes in their responses to osmotic or salt stress. Therefore, the plant stresses studied in objective 1 were expanded to include high temperature to tie the project to global climate change, because high temperature changes both plant growth and its regulation by the circadian clock. The genes needed for plants to sense and respond to a warmer environment are not well defined. To identify genes involved in responses to elevated temperature, a mutant screen was initiated in Arabidopsis and more than five novel mutants were identified. Under objective 2, the DNA sequence of the promoter regions for two circadian clock genes harboring conserved regulatory elements were cloned into reporter constructs, which will be used to make transgenic plants for the study of conserved regulatory elements that control circadian gene expression in maize. Under objectives 3 and 4, genetic studies continued with maize mutants, which knock out expression of circadian clock genes in order to fully establish where the circadian clock regulates maize growth and development. Furthermore, additional mutants were identified in other likely circadian clock genes and these were preliminarily characterized for miss-regulation of growth.