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AtSIG6, a plastid sigma factor from Arabidopsis, reveals functional impact of cpCK2 phosphorylation
Author(s) -
Schweer Jennifer,
Türkeri Hacer,
Link Brigitte,
Link Gerhard
Publication year - 2010
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2010.04138.x
Subject(s) - biology , phosphorylation , arabidopsis , serine , transcription factor , sigma factor , complementation , kinase , microbiology and biotechnology , plastid , casein kinase 2 , mutant , genetics , protein kinase a , transcription (linguistics) , gene , biochemistry , promoter , gene expression , cyclin dependent kinase 2 , chloroplast , linguistics , philosophy
Summary Plastids contain sigma factors, i.e. gene‐regulatory proteins for promoter binding and transcription initiation. Despite the physical and functional similarity shared with their prokaryotic counterparts, the plant sigma factors have distinguishing features: most notably the existence of a variable extra sequence comprising their N‐terminal portions. This distinct architecture is reflected by functional differences, including phosphorylation control by organellar protein kinase(s) closely related to nucleocytosolic, rather than bacterial‐type, enzymes. In particular, cpCK2, a nuclear‐coded plastid‐targeted casein kinase 2, has been implicated as a key component in plant sigma factor phosphorylation and transcriptional regulation ( Eur. J. Biochem. 269, 2002, 3329; Planta , 219, 2004, 298). Although this notion is based mainly on biochemical evidence and in vitro systems, the recent availability of Arabidopsis sigma knock‐out lines for complementation by intact and mutant sigma cDNAs has opened up new strategies for the study of transcription regulatory mechanisms in vivo . Using Arabidopsis sigma factor 6 (AtSIG6) as a paradigm, we present data suggesting that: (i) this factor is a substrate for regulatory phosphorylation by cpCK2 both in vitro and in vivo ; (ii) cpCK2 phosphorylation of SIG6 occurs at multiple sites, which can widely differ in their effect on the visual and/or molecular phenotype; (iii) in vivo usage of the perhaps most critical cpCK2 site defined by Ser174 requires (pre‐)phosphorylation at the n + 3 serine residue Ser177, pointing to ‘pathfinder’ kinase activity capable of generating a functional cpCK2 substrate site.