PII is induced by WRINKLED1 and fine-tunes fatty acid composition in seeds of Arabidopsis thaliana

Abstract

The Pll protein is an integrator of central metabolism and energy levels. In Arabidopsis, allosteric sensing of cellular energy and carbon levels alters the ability of Pll to interact with target enzymes such as N-acetyl-L-glutamate kinase and heteromeric acetyl-coenzyme A carboxylase, thereby modulating the biological activity of these plastidial ATP- and carbon-consuming enzymes. A quantitative reverse transcriptase-polymerase chain reaction approach revealed a threefold induction of the At G LB 1 gene (At4g01900) encoding Pll during early seed maturation. The activity of the At G LB 1 promoter was consistent with this pattern. A complementary set of molecular and genetic analyses showed that WRINKLED1, a transcription factor known to induce glycolytic and fatty acid biosynthetic genes at the onset of seed maturation, directly controls AtGLBI expression. Immunoblot analyses and immunolocalization experiments using anti-PII antibodies established that Pll protein levels faithfully reflected AtGLBI mRNA accumulation. At the subcellular level, Pll was observed in plastids of maturing embryos. To further investigate the function of Pll in seeds, comprehensive functional analyses of two pll mutant alleles were carried out. A transient increase in fatty acid production was observed in mutant seeds at a time when Pll protein content was found to be maximal in wild-type seeds. Moreover, minor though statistically significant modifications of the fatty acid composition were measured in pll seeds, which exhibited decreased amounts of modified (elongated, desaturated) fatty acid species. The results obtained outline a role for Pll in the fine tuning of fatty acid biosynthesis and partitioning in seeds. © 2010 Blackwell Publishing Ltd.