2011 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 organism 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.
Under Objective 1, established that the rapid flowering of Arabidopsis plants, which is induced by high temperature, is a response specifically to the high temperature during the night. Circadian clock-regulated transcription factors involved in light signaling are required for this developmental shift. Under Objectives 3 and 4, developed mutants in corn plants, with important assistance from the ongoing CRADA with Pioneer Hi-Bred, that accelerate flowering time and shorten plant stature, as well as have the potential to alter circadian rhythms. These findings demonstrate the plant circadian clock regulates important aspects of corn development.
Circadian clock regulated transcription factors control flowering time at elevated temperatures. Plants adjust their growth in response to temperature signals, but how plants sense a warmer environment is unknown. High temperature effects on plant growth were evaluated in mutants that control plant development. ARS scientists in Albany, CA, found elevated temperatures during the night cause more rapid flowering with the requirment of circadian clock-regulated transcription factors. These mutants will help to examine the regulatory systems governing the timing of flowering in response to temperature signals. This research provides a basic understanding of how plants respond to warmer environments and is relevant to the effect of global climate change on plant development.
Inactivation of the maize circadian clock gene GIGANTEAA1 speeds flowering time. Optimal plant growth requires appropriate respnses to environmental cues. Plants exhibit circadian-clock regulation of their development. Knock out mutants in GIGANTEAA1 were analyzed for obvious developmental alterations by ARS scientists in Albany, CA. Knock out of maize GIGANTEAA1 function by transposon insertion caused earlier flowering and shorter plant stature. This gene is vital for maize plants to correctly switch to floral development and indicate circadian rhythms are important for this aspect of maize development. This research defines the regulatory systems governing the timing of flowering in maize and provides an understanding of how maize plant growth responds to environmental signals.
Thines, B., Harmon, F.G. 2010. Four easy pieces: mechanisms underlying circadian regulation of growth and development. Current Opinion in Plant Biology. 14:1–7.