Mutations in CHLOROPLAST RNA BINDING provide evidence for the involvement of the chloroplast in the regulation of the circadian clock in Arabidopsis

• Published in: The Plant journal : for cell and molecular biology 2007-08, Vol.51 (4), p.551-562
• Main Authors: Hassidim, Miriam, Yakir, Esther, Fradkin, David, Hilman, Dror, Kron, Ido, Keren, Nir, Harir, Yael, Yerushalmi, Shai, Green, Rachel M
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - ultrastructure; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Biological and medical sciences; Blotting, Northern; Botany; Cell structures and functions; Cellular biology; chloroplast; Chloroplast, photosynthetic membrane and photosynthesis; Chloroplasts - genetics; Chloroplasts - metabolism; Chloroplasts - ultrastructure; circadian; Circadian rhythm; Circadian Rhythm - genetics; Fundamental and applied biological sciences. Psychology; Gene expression; Gene Expression Regulation, Plant; Microscopy, Electron, Transmission; Molecular and cellular biology; Mutation; Plants, Genetically Modified; retrograde signaling; RNA binding; RNA, Plant - genetics; RNA, Plant - metabolism; RNA-Binding Proteins - genetics; RNA-Binding Proteins - metabolism; Signal transduction; signaling
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313x.2007.03160.x

The Arabidopsis circadian system regulates the expression of up to 36% of the nuclear genome, including many genes that encode photosynthetic proteins. The expression of nuclear-encoded photosynthesis genes is also regulated by signals from the chloroplasts, a process known as retrograde signaling. We have identified CHLOROPLAST RNA BINDING (CRB), a putative RNA-binding protein, and have shown that it is important for the proper functioning of the chloroplast. crb plants are smaller and paler than wild-type plants, and have altered chloroplast morphology and photosynthetic performance. Surprisingly, mutations in CRB also affect the circadian system, altering the expression of both oscillator and output genes. In order to determine whether the changes in circadian gene expression are specific to mutations in the CRB gene, or are more generally caused by the malfunctioning of the chloroplast, we also examined the circadian system in mutations affecting STN7, GUN1, and GUN5, unrelated nuclear-encoded chloroplast proteins known to be involved in retrograde signaling. Our results provide evidence that the functional state of the chloroplast may be an important factor that affects the circadian system.