Department of Biology

Our lab is interested in the physiological and molecular mechanisms by which plants perceive and respond to environmental stimuli. Together, light and gravity have profound effects on plant development and much of our research focuses on how plants integrate the information from these environmental stimuli in order to understand how various environmental sensory responses function and interact to coordinately regulate plant growth and development.

We use the model plant Arabidopsis thaliana as our experimental system. Mutant strains are identified that have altered responses, such as gravitropism. Genetic and molecular approaches are then used to identify and characterize the cause of the mutant phenotypes, including cloning the mutated genes for molecular analyses. Comparative physiological studies of mutant and wild-type strains are also conducted to determine the functional role of the different processes during normal plant development.

Current Research Projects

Tropisms: Tropisms are directional responses to external stimuli. Most research on gravitropism and phototropism has focused on the primary root and shoot of young seedlings. However, most other parts of a plant do not grow parallel to the gravity vector. Variation in the orientation of the lateral parts of plants give rise to a diversity of plant form. The orientations of lateral parts of plants is to a large extent affected by environmental factors such as light. Moreover, lateral organs appear to actively maintain their orientation at a Gravitropic Set-point Angle (GSA). Our research on plant tropisms is focused on understanding how the lateral organs of plants use light and gravity to guide their growth at the correct angle. We are using a combination of physiological and genetic approaches. Specifically, we have identified several novel mutants in Arabidopsis that have altered orientation of lateral organs, including leaves, branches and lateral roots while retaining normal orientation of the primary shoot and root. We are cloning and characterizing the respective genes and conducting physiological and molecular investigations to gain insight into the mechanism of GSA maintenance and the mechanism of lateral organ gravitropism. Our research is elucidating the molecular basis of the GSA and the mechanisms involved in the transduction of directional information into the organ polarity necessary for differential growth responses. Funded by NASA.

Light-Induced Chloroplast Movements: Chloroplast movements are light-directed responses that occur in a number of diverse plant groups including algae, moss, ferns, and angiosperms. In species that contain multiple chloroplasts per cell, exposure to dim-light causes chloroplasts to accumulate along cell walls oriented perpendicular to the incident light. When the fluence rate of light is high, chloroplasts migrate to the anticlinal walls, parallel to the incident light. These movements are thought to provide important adjustments for maintaining maximal photosynthetic performance in a variable light environment. We have identified a number of mutants that affect light-induced chloroplast movements in Arabidopsis. Using our mutant collection, we have identified several genes that are required for normal light-induced chloroplast movements. The mutants and genes we have identified are providing new insights into the mechanism by which the actin cytoskeleton causes and regulates the movements as well as new insights into the adaptive function of chloroplast movements to the physiology of plants. Funded by NSF.

Chloroplast Development: We are investigating plastid development during late embryogenesis and early germination. We have identified several genes that interfere with the normal differentiation of chloroplasts during late stages of embryo maturation. Mutant version of these genes result in seedlings with white cotyledons. However, the true leaves develop normal green chloroplasts. One of the genes (SPD1) is also involved in amyloplast development. Investigation of this class of mutants provides a unique opportunity to investigate a critical, but poorly understood, stage of plastid development. This research is providing new understanding of the mechanisms that control critical stages of chloroplast and amyloplast differentiation. Funded by DOE.