The Steber Laboratory is part of the Wheat Genetics, Quality, Physiology, and Disease Research Unit, United States Department of Agriculture, Agricultural Research Service, and is housed in and affiliated with the Department of Crop and Soil Sciences, at Washington State University in Pullman, Washington. The principal investigator is Camille Steber, and the lab was started in 1998.
The Steber Laboratory is focused on the study of hormonal control of seed dormancy and germination, as well as plant stress responses. Basic research projects are carried out in the Arabidopsis thaliana model system, and knowledge from Arabidopsis is translated into improved resistance to preharvest sprouting and drought tolerance in wheat. Seed dormancy and germination are controlled by the balance between the abscisic acid (ABA) and gibberellin (GA) hormone signalling pathways. ABA induces seed dormancy during embryo maturation, whereas GA stimulates seed germination and is associated with dormancy breaking treatments such as cold stratification and dry after-ripening. Research in Arabidopsis is focused on understanding the mechanisms of GA signaling, and the relative roles of ABA and GA in the control of seed dormancy, dormancy loss, and germination. In addition to stimulating seed germination, GA also stimulates stem elongation, the transition to flowering, and fertility. Research in wheat is aimed at increasing preharvest sprouting (PHS) and drought tolerance using increased ABA sensitivity.
The Steber Laboratory uses mutation breeding as a tool for wheat improvement. The main effort uses wheat mutants with altered response to the hormone ABA to control wheat grain dormancy and drought tolerance. Wheat production is subject to risk of yield loss due to drought and to preharvest sprouting (PHS), the germination of mature grain (caryopses) on the mother plant when cool moist conditions persist close to harvest time. When PHS occurs grain must be sold as feed, causing considerable economic losses to farmers. PHS is associated with lack of grain dormancy and sensitivity to the plant hormone abscisic acid (ABA) in wheat. ABA stimulates dormancy as well as adaptive responses to drought, cold and salt stress. Our research examines whether higher PHS tolerance is associated with higher ABA sensitivity or decreased GA sensitivity. Another major effort is a collaborative project with Dr. Kimberly Garland Campbell and Dr. Scot Hulbert to improve wheat drought tolerance through multiple mechanisms such as increased water use efficiency, mobilization of water-soluble carbohydrates, and altered root architecture. In an ongoing collaboration with Dr. Kimberlee K. Kidwell and Dr. Ian Burke, the laboratory is helping to analyze wheat variants with increased resistance to the herbicide glyphosate. In the past, the laboratory made contributions to improving Rhizoctonia root rot tolerance, tissue culture, and developed a floral dip method for wheat transformation. See the publications page for more information on our work.
GA stimulation of seed germination requires the down-regulation of negative regulators of seed germination called the DELLA domain proteins. DELLAs are down-regulated both by protein destruction via the ubquitin-proteasome pathway and by direct interaction with the GA receptors. DELLA proteolysis occurs in response to GA biosynthesis and requires three functionally redundant GA receptors GIBBERELLIN INSENSITIVE DWARF1 (GID1a, GID1b and GID1c), and the SLEEPY1 (SLY1) F-box subunit of an SCF E3 ubiquitin ligase. In sly1 mutants in which DELLA proteins remain stable after GA application, the DELLA repressor can also be down-regulated either by after-ripening or by overexpression of the GA receptor, GID1. This requires GA biosynthesis and the presence of a functional DELLA domain. Both the DELLA motif and GA are required for the protein interaction of DELLA protein and GID1. Ongoing research is aimed at further elucidating the non-proteolytic mechanism for DELLA regulation and its functional role in seed dormancy loss and germination. Co-immunoprecipitation will be used to determine whether dormancy-breaking treatments stimulate the interaction of DELLA with the GID1 receptor. Also, microarray analysis will be used to examine the effect of the sly1 mutation on gene expression during seed imbibition. See the publications page for more information on our work.