Location: Sunflower and Plant Biology Research2012 Annual Report
1a. Objectives (from AD-416):
The specific objectives are 1) to define and clarify biological factors, mechanisms, and pathways that regulate reproduction and dormancy in vegetative propagules of perennial weeds, including, but not limited to leafy spurge (Euphorbia esula) and Canada thistle (Cirsium arvense); and 2) to define and clarify biological factors, mechanisms, and pathways that regulate seed dormancy and germination in weeds, including, but not limited to leafy spurge (Euphorbia esula).
1b. Approach (from AD-416):
Weeds are a major pest leading to reduced production of the nation’s food and fiber crops. They also negatively impact natural ecosystems. Certain characteristics of weeds, such as dormancy of reproductive structures account for their persistence, survival, and ability to escape control methods. Leafy spurge (Euphorbia esula) is a noxious perennial weed in the Northern Great Plains due to its negative impacts in rangeland and natural lands. Similarly, Canada thistle is a serious perennial weed worldwide in many natural and agroecosystems. Leafy spurge displays para-, endo-, and eco-dormancy in underground adventitious crown and root bud, as well as seed dormancy. This project will focus on leafy spurge and utilize Canada thistle for comparative purposes for the investigation of paradormancy. Thus, the project will employ physiological, biochemical, molecular, and genomic approaches to elucidate regulatory mechanisms, signals, and pathways related to dormancy. The long-term goal of this project is to increase fundamental knowledge about dormancy in leafy spurge and other perennial weeds to facilitate development of improved and new weed management strategies.
3. Progress Report:
Leafy spurge and Canada thistle are noxious perennial weeds used to investigate dormancy in buds and seeds. Microarray data related to the effects of alternating temperature on germinability of leafy spurge seeds and on abiotic stress (e.g., dehydration) as it relates to vegetative reproduction from leafy spurge crown and root buds was analyzed and manuscripts are being prepared. A final manuscript was prepared and published on cloning and characterization of Rc, which is the underlying gene for qSD7-1. Collaborative studies are underway to determine temperature effects on after-ripening in wild and domesticated sunflower seeds. Chromatin associated with DAM1 and DAM2 during endo- and eco-dormancy was precipitated, and in collaboration with the University of Texas, DAM genes were shown to be associated with the FT gene. We have developed constructs to express DAM1, DAM2, the poplar homologue MADS27, and the reporter gene GUS under control of the cold-induced DAM1 promoter. In collaboration with UC Riverside, transformation experiments using different Agrobacterium strains and T-DNA binary vector combinations are being done to further examine the function DAM and other gene in leafy spurge. Quantitative real-time polymerase chain reaction (qRT-PCR) is the most important tool in measuring levels of gene expression due to its accuracy, specificity, and sensitivity. We validated the expression stability of four candidate reference genes for analyses of leafy spurge qRT-PCR data. The reference genes are being utilized in expression studies related to growth, hormones, light, temperature response/regulation, and abiotic stress in bud and seed of leafy spurge. A leafy spurge BAC library was screened and clones containing DAM, FT, beta-amylase, and dormancy-regulated AP2-type transcription factor genes were identified. Sequence these BAC clones using the new Pacific BioSciences sequencing technology was unsuccessful; thus, Illumina sequencing has been initiated. A full genome sequencing of the leafy spurge genome using Illumina technology has been initiated to augment the BAC sequencing and identify promoter sequences from a majority of the leafy spurge genes. Transcriptome and hormone analyses of paradormancy in Canada thistle have been completed. Ethylene levels and proteins involved in ethylene biosynthesis during growth and paradormancy release of leafy spurge buds were examined. Transcriptome and hormone analysis experiments are underway examining glyphosate-induced witches’ brooming of leafy spurge crown and root buds.
1. Plant hormones regulate dormancy in root sections of Canada thistle. Perennial weeds, such as Canada thistle, are particularly problematic in conventional and organic farming system and natural areas as they can escape control measures and spread from hundreds of buds on the underground root system. Knowing that root bud dormancy in Canada thistle is released by cutting roots during soil tillage, ARS researchers in Fargo, ND, investigated global patterns of gene expression at several time points after sectioning the roots. Analyses of the 15,232 uniquely expressed gene sequences identified processes involved in plant hormone signaling networks. Examination of hormone profiles in root sections suggested specific plant hormones that are of importance in root sections containing vegetative buds. This new knowledge may lead to a new control strategy based on simultaneous bud dormancy release that could significantly improve control methods for perennial weeds.
2. Red grain color regulates seed dormancy in weedy rice. Seed dormancy allows weeds to escape chemical control measures knowing that seed dormancy and resistance to pre-harvest sprouting is ultimately regulated by genes, ARS researchers in Fargo, ND, in collaboration with university partners at South Dakota State University developed weedy rice as a system to locate and characterize genes that regulate seed dormancy and resistance to pre-harvest sprouting of cereal grains. They discovered that a gene called Rc, which codes for red grain color, also regulates seed dormancy and germination by inducing the expression of genes for the biosynthesis of a dormancy-inducing hormone called abscisic acid. This new knowledge may lead to new strategies to manipulate seed dormancy and germination that could significantly improve weed control methods and provide the means to reduce the incidence of pre-harvest sprouting in cereal grain crops.
Foley, M.E., Chao, W.S., Dogramaci, M., Horvath, D.P., Anderson, J.V. 2012. Changes in the transcriptome of dry leafy spurge (Euphorbia esula) seeds imbibed at a constant and alternating temperature. Weed Science. 60(1):48-56.