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BMC Plant Biol. 2012; 12: 102.
Published online Jul 8, 2012. doi:  10.1186/1471-2229-12-102
PMCID: PMC3409070
The plastid-localized pfkB-type carbohydrate kinases FRUCTOKINASE-LIKE 1 and 2 are essential for growth and development of Arabidopsis thaliana
Jonathan Gilkerson,1,2,3 Juan Manuel Perez-Ruiz,3,4 Joanne Chory,3,4 and Judy Calliscorresponding author1,2
1Department of Molecular and Cellular Biology, University of California, 1 Shields Avenue, Davis, CA, 95616, USA
2Plant Biology Graduate Group, University of California, Davis, CA, 95616, USA
3Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA, 92037, USA
4Howard Hughes Medical Institute, The Salk Institute for Biological Studies, La Jolla, CA, 92037, USA
corresponding authorCorresponding author.
Jonathan Gilkerson: jgilkerson/at/salk.edu; Juan Manuel Perez-Ruiz: jperez/at/salk.edu; Joanne Chory: jchory/at/salk.edu; Judy Callis: jcallis/at/ucdavis.edu
Received April 17, 2012; Accepted July 8, 2012.
Abstract
Background
Transcription of plastid-encoded genes requires two different DNA-dependent RNA polymerases, a nuclear-encoded polymerase (NEP) and plastid-encoded polymerase (PEP). Recent studies identified two related pfkB-type carbohydrate kinases, named FRUCTOKINASE-LIKE PROTEIN (FLN1 and FLN2), as components of the thylakoid bound PEP complex in both Arabidopsis thaliana and Sinapis alba (mustard). Additional work demonstrated that RNAi-mediated reduction in FLN expression specifically diminished transcription of PEP-dependent genes.
Results
Here, we report the characterization of Arabidopsis FLN knockout alleles to examine the contribution of each gene in plant growth, chloroplast development, and in mediating PEP-dependent transcription. We show that fln plants have severe phenotypes with fln1 resulting in an albino phenotype that is seedling lethal without a source of exogenous carbon. In contrast, fln2 plants display chlorosis prior to leaf expansion, but exhibit slow greening, remain autotrophic, can grow to maturity, and set viable seed. fln1 fln2 double mutant analysis reveals haplo-insufficiency, and fln1 fln2 plants have a similar, but more severe phenotype than either single mutant. Normal plastid development in both light and dark requires the FLNs, but surprisingly skotomorphogenesis is unaffected in fln seedlings. Seedlings genetically fln1-1 with dexamethasone-inducible FLN1-HA expression at germination are phenotypically indistinguishable from wild-type. Induction of FLN-HA after 24 hours of germination cannot rescue the mutant phenotype, indicating that the effects of loss of FLN are not always reversible. Examination of chloroplast gene expression in fln1-1 and fln2-1 by qRT-PCR reveals that transcripts of PEP-dependent genes were specifically reduced compared to NEP-dependent genes in both single mutants.
Conclusions
Our results demonstrate that each FLN protein contributes to wild type growth, and acting additively are absolutely essential for plant growth and development.
Keywords: pfkB-type carbohydrate kinase, FLN, Chloroplast transcription, pTAC complex, Arabidopsis thaliana
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