Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 26, Pages 10780-10785Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1104242108
Keywords
phytochrome; transcription regulator; two-component signaling; UV-A sensor
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Funding
- Advanced Biomass Research and Development Center [2010-0029728]
- Agricultural Genomics Center of Korea [PJ8205]
- National Institutes of Health [GM068552, DOE DE-FG02-09ER16117]
- Department of Energy Office of Basic Energy Biosciences
- Rural Development Administration (RDA), Republic of Korea [PJ00820520111139300] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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Positive phototaxis systems have been well studied in bacteria; however, the photoreceptor(s) and their downstream signaling components that are responsible for negative phototaxis are poorly understood. Negative phototaxis sensory systems are important for cyanobacteria, oxygenic photosynthetic organisms that must contend with reactive oxygen species generated by an abundance of pigment photosensitizers. The unicellular cyanobacterium Synechocystis sp. PCC6803 exhibits type IV pilus-dependent negative phototaxis in response to unidirectional UV-A illumination. Using a reverse genetic approach, together with biochemical, molecular genetic, and RNA expression profiling analyses, we show that the cyanobacteriochrome locus (slr1212/uirS) of Synechocystis and two adjacent response regulator loci (slr1213/uirR and the PatA-type regulator slr1214/lsiR) encode a UV-A-activated signaling system that is required for negative phototaxis. We propose that UirS, which is membrane-associated via its ETR1 domain, functions as a UV-A photosensor directing expression of lsiR via release of bound UirR, which targets the lsiR promoter. Constitutive expression of LsiR induces negative phototaxis under conditions that normally promote positive phototaxis. Also induced by other stresses, LsiR thus integrates light inputs from multiple photosensors to determine the direction of movement.
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