Structural and Functional Analysis of the Bacteriophytochrome Photoreceptors: Models for the Phytochrome Superfamily

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A complex array of photoreceptors help cellular organisms detect and respond to their light environment. One of the most influential is the phytochrome superfamily, a large and diverse group of photoreceptors present in both prokayotes and eukaryotes. They are photochromic pigments that use a linear tetrapyrrole or bilin chromophore to sense red and far-red light. Phytochrome-type photoreceptors were first discovered in higher plants by their ability to initiate numerous photoresponses critical for agricultural productivity. More recently, they have been shown to also exist in various microorganisms, including cyanobacteria, eubacteria, fungi and slime molds. The goal of this research project is to further understand how phytochromes function through an in-depth analysis of the bacteriophytochrome subfamily, a collection of related phytochromes that were recently discovered in bacteria and fungi. These bacteriophytochromes offer an attractive opportunity to study phytochromes in simple genetically-tractable organisms that possess few photoreceptors and lack the complications of photosynthesis, and the ability to generate ample quantities of homogeneous and stable pigment needed for structural analyses. This project specifically will attempt to: (1) solve the first three-dimensional structure of a phytochrome-type photoreceptor by X-ray diffraction analyses of bacteriophytochrome crystals, and (2) exploit various genomic methods to define how these photoreceptors function in microorganisms. Completion of this research will provide the first detailed picture of how phytochromes work mechanistically and affect the behavior of microorganisms. More broadly, this work will ultimately help elucidate how higher plants sense their light environment via this unique photoreceptor type and thus could have important agricultural implications. In addition, the research will enhance scientific infrastructure via a cooperative college/university arrangement for the training of postdoctoral, graduate and undergraduate students in modern molecular techniques.