title: A shadow detector for photosynthesis efficiency.
abstract: Plants tolerate large variations in the intensity of the light environment by controlling the efficiency of solar to chemical energy conversion. To do this, plants have a mechanism to detect the intensity, duration, and change in light as they experience moving shadows, flickering light, and cloud cover. Sugars are the primary products of CO2fixation, a metabolic pathway that is rate limited by this solar energy conversion. We propose that sugar is a signal encoding information about the intensity, duration and change in the light environment. We previously showed that the Arabidopsis heterotrimeric G protein complex including its receptor-like Regulator of G signaling protein, AtRGS1, detects both the concentration and the exposure time of sugars (Fu et al., 2014. Cell 156: 1084-1095). This unique property, designated dose-duration reciprocity, is a behavior that emerges from the system architecture / system motif. Here, we show that another property of the signaling system is to detect large changes in light while at the same time, filtering types of fluctuation in light that do not affect photosynthesis efficiency. When AtRGS1 is genetically ablated, photosynthesis efficiency is reduced in a changing- but not a constant-light environment. Mathematical modeling revealed that information about changes in the light environment is encoded in the amount of free AtRGS1 that becomes compartmentalized following stimulation. We propose that this property determines when to adjust photosynthetic efficiency in an environment where light intensity changes abruptly caused by moving shadows on top of a background of light changing gradually from sun rise to sun set and fluctuating light such as that caused by fluttering leaves.
authors.affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Kang-Ling
authors.initials: KL
authors.lastname: Liao
authors.affiliation: Center for Complex Systems and Enterprises, Stevens Institute of Technology, Hoboken, NJ 07030, USA.
authors.forename: Roger D
authors.initials: RD
authors.lastname: Jones
authors.affiliation: Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: McCarter
authors.affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Meral
authors.initials: M
authors.lastname: Tunc-Ozdemir
authors.affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Draper
authors.affiliation: Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. Electronic address: timothy_elston@med.unc.edu.
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Elston
authors.affiliation: Plant Research Laboratory Michigan State University, East Lansing, MI, USA.
authors.forename: David
authors.initials: D
authors.lastname: Kramer
authors.affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. Electronic address: alan_jones@unc.edu.
authors.forename: Alan M
authors.initials: AM
authors.lastname: Jones
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D020710:RGS Proteins / Q000378:metabolism*; D013472:Sunlight
chemical_list: D029681:Arabidopsis Proteins; D020710:RGS Proteins; C477755:RGS1 protein, Arabidopsis; D002245:Carbon Dioxide; D020962:Heterotrimeric GTP-Binding Proteins
keywords: Endocytosis; Heterotrimeric G protein; Photosynthesis efficiency; Regulator of G signaling; Shadow detector; WNK kinase