Ah-Young Shin1,†,*, Yun-Jeong Han1,*, Ayoung Baek2, Taeho Ahn3, Soo Young Kim1, Thai Son Nguyen1, Minky Son2, Keun Woo Lee2, Yu Shen4,†, Pill-Soon Song5 & Jeong-Il Kim1
1 Department of Biotechnology and Kumho Life Science Laboratory, Chonnam National University, Gwangju 500-757, Korea. 2 Division of Applied Life Science (BK21 Plus Program), Systems and Synthetic Agrobiotech Center (SSAC), Plant Molecular Biology and Biotechnology Research Center (PMBBRC), Research Institute of Natural Science (RINS), Gyeongsang National University, Jinju 660-701, Korea. 3 College of Veterinary Medicine, Chonnam National University, Gwangju 500-757, Korea. 4 BioVision Inc., Milpitas, California 95035, USA. 5 Faculty of Biotechnology and Subtropical Horticulture Research Institute, Jeju National University, Jeju 690-756, Korea. † Present address: Molecular Biofarming Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejon 305-806, Korea (A.-Y.S.); BASF Plant Science, 26 Davis Drive, Research Triangle Park, North Carolina 27709, USA (Y.S.).
* These authors contributed equally to this work.
Correspondence to : Jeong-Il Kim
It has been suggested that plant phytochromes are autophosphorylating serine/threonine kinases. However, the biochemical properties and functional roles of putative phytochrome kinase activity in plant light signalling are largely unknown. Here, we describe the biochemical and functional characterization of Avena sativa phytochrome A (AsphyA) as a potential protein kinase. We provide evidence that phytochrome-interacting factors (PIFs) are phosphorylated by phytochromes in vitro. Domain mapping of AsphyA shows that the photosensory core region consisting of PAS-GAF-PHY domains in the N-terminal is required for the observed kinase activity. Moreover, we demonstrate that transgenic plants expressing mutant versions of AsphyA, which display reduced activity in in vitro kinase assays, show hyposensitive responses to far-red light. Further analysis reveals that far-red light-induced phosphorylation and degradation of PIF3 are significantly reduced in these transgenic plants. Collectively, these results suggest a positive relationship between phytochrome kinase activity and photoresponses in plants.