Joon-Yung Cha1, Jeongsik Kim2,3, Tae-Sung Kim2,4, Qingning Zeng2, Lei Wang 2,5, Sang Yeol Lee1, Woe-Yeon Kim1 & David E. Somers2
1 Division of Applied Life Science (BK21Plus), PMBBRC &IALS, Gyeongsang National University, Jinju 52828, Republic of Korea. 2 Department of Molecular Genetics, The Ohio State University, Columbus 43210, USA. 3Present address: Center for Plant Aging Research, Institute for Basic Science (IBS), Daegu 711-873, Republic of Korea. 4Present address: Department of Agricultural Sciences, Korea National Open University, Seoul 03087, Republic of Korea. 5Present address: Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China. Joon-Yung Cha and Jeongsik Kim contributed equally to this work.
Correspondence : Woe-Yeon Kim, David E. Somers
Circadian clock systems help establish the correct daily phasing of the behavioral, developmental, and molecular events needed for the proper coordination of physiology and metabolism. The circadian oscillator comprises transcription.translation feedback loops but also requires post-translational processes that regulate clock protein homeostasis. GIGANTEA is a unique plant protein involved in the maintenance and control of numerous facets of plant physiology and development. Through an unknown mechanism GIGANTEA stabilizes the F-box protein ZEITLUPE, a key regulator of the circadian clock. Here, we show that GIGANTEA has general protein chaperone activity and can act to specifically facilitate ZEITLUPE maturation into an active form in vitro and in planta. GIGANTEA forms a ternary complex with HSP90 and ZEITLUPE and its co-chaperone action synergistically enhances HSP90/HSP70 maturation of ZEITLUPE in vitro. These results identify a molecular mechanism for GIGANTEA activity that can explain its wide-ranging role in plant biology.