José R. Dinneny, PhD
Carnegie Institution for Science
Department of Plant Biology
260 Panama St.
Stanford, CA 94305
YouTube video of presentation on "Roots and the hidden half of plant biology"
Press releases covering our work:
Hydropatterning, a newly discovered environmental response to water controls branching.
Salt stress is controlled by endodermal ABA signaling.
Cells must constantly assess current environmental conditions and generate an output that is contextually appropriate. The elegantly simple organization of the root provides a unique opportunity to explore these processes in a multi-cellular organ with the goal of discovering fundamental principles of signal integration that also apply to other biological systems. Our research is aimed at understanding four questions:
• How does spatial and temporal information regulate the response and acclimation of the root to high salinity?
• How does information encoded in the promoter enable a gene to be environmentally responsive?
• How is moisture in the environment sensed by the root and how does local variation in moisture affect the patterning of tissues?
• How does the soil environment affect the biology of the root?
Salinity research in the Dinneny lab
Today, humanity is increasingly aware of the impact it has on the environment and the difficulties caused when the environment impacts our communities. Environmental change can be particularly harsh when the plants we use for food, fuel, feed and fiber are affected by this change. High salinity is an agricultural contaminant of increasing significance. Not only does this limit the land available for use in agriculture, but in land that has been used for generations, the combination of irrigation and evaporation gradually leads to increasing soil salinity.
Our lab focuses on understanding how developmental processes such as cell-type specification regulate responses to environmental change. While understanding the mechanisms controlling environmental response is a major focus in plant biology, most studies have considered the organ or even the whole organism as a single responsive unit and ignore the potential diversity of responses that may be afforded by the various cell-types composing an organism. We have shown that developmental parameters play a key role in determining the transcriptional response of cells to high salinity.
In Previous work we used Fluorescence Activated Cell Sorting to isolate specific cell-types from roots, we were able to generate a high-resolution gene expression map (Dinneny et al., 2008). This map details the expression pattern of over 23,000 Arabidopsis genes in roots grown under both standard and high-salinity conditions. With this expression map, we have shown that previously characterized regulatory pathways primarily control transcriptional events occurring in multiple cell-types while cell-type specific responses, which constitute the bulk of the response, are controlled by unknown mechanisms. Identifying and characterizing these unknown mechanisms is at the heart of our current research. This work will lead to a deep understanding of how a multicellular organ responds and potentially adapts to environmental change and will break new ground connecting upstream developmental pathways to downstream physiology. We have recently defined the tissues where stress hormones act to regulate root growth (Duan et al., 2013) and developed a novel spatiotemporal transcriptional map of the salt stress response (Geng et al., 2013). These studies reveal at unparalleled resolution the mechanism controlling aclimation to this important environmental stress.
Deciphering the cis-regulatory code controlling cell-type specific responses to salt stress
Understanding the mechanisms controlling gene expression patterns remains a central question in biology. While many studies begin and end with the characterization of a single cis-regulatory element, the goal of our current work is to develop a comprehensive understanding of the many different sequences that contribute to the salt-stress response. As the cost of gene synthesis has fallen, we have devised a synthetic biology approach to cis- element analysis. We are constructing synthetic regulatory regions containing predicted cis- element sequences identified using various computational algorithms (FIRE, cERMIT, Athena). We are generating synthetic regulatory regions for these putative elements and will test whether these sequences are sufficient to drive spatial or environmentally regulated expression patterns in the root.
Novel cis-elements found to be important will provide a valuable resource for identifying the associated TFs. Our synthetic promoters provide ideal baits in yeast-1-hybrid screens to identify the associated TFs. These data will be used to generate a cis-element centered transcriptional networks, which will aid in understanding how complex patterns of expression are generated during environmental stress. This project is in collaboration with Steve Kay and José Pruneda-Paz at the University of California, San Diego.
Understanding the mechanisms governing "hydropatterning" in roots
Fresh water constitutes less than 1% of the surface water on earth, yet the importance of this simple molecule to all life forms is immeasurable. Water represents the most vital reagent for chemical reactions occurring in a cell. In plants, water provides the structural support necessary for plant growth. It acts as the carrier for nutrients absorbed from the soil and transported to the shoot. It also provides the chemical components necessary to generate sugar and biomass from light and carbon dioxide during photosynthesis. While the importance of water to plants is clear, an understanding as to how plants perceive water is limited. Most studies have focused on environmental conditions in which severe limitation (drought) or severe excess (flooding) of water is simulated. While these are important stress conditions, the plant may also sense and respond to differences in moisture content under non-stress conditions. Much as how light can act as a signal or a stress depending on the intensity, water may also have such a dual effect. In support of this hypothesis, work on hydrotropism has shown that roots have the ability to sense moisture gradients and direct growth towards favorable conditions.
Our current studies indicate that moisture signaling may extend beyond hydrotropism and regulate nearly every aspect of root development. In a process we term "hydropatterning", local contact of the root tip with a liquid or air environment has the ability to cause stark differences in the development of tissues. Hydropatterning is observed in Arabidopsis thaliana as well as other flowering plants. The goal of our current research is to establish a foundation for understanding hydropatterning by characterizing the changes in growth and development that are directly affected. Using developmental and cell-type specific approaches along with genetic and genomic tools, our research will identify the key pathways through which moisture signaling acts to affect these processes. This work was recently published in PNAS (Bao et al., 2014) and forms the basis for our current studies to understand the mechanisms controlling these responses.