Barley grains, deficient in cytosolic small subunit of ADP-glucose pyrophosphorylase, reveal coordinate adjustment of C:N metabolism mediated by an overlapping metabolic-hormonal control
Article first published online: 10 JAN 2012
© 2011 The Authors. The Plant Journal © 2011 Blackwell Publishing Ltd
The Plant Journal
Volume 69, Issue 6, pages 1077–1093, March 2012
How to Cite
Faix, B., Radchuk, V., Nerlich, A., Hümmer, C., Radchuk, R., Emery, R.J. N., Keller, H., Götz, K.-P., Weschke, W., Geigenberger, P. and Weber, H. (2012), Barley grains, deficient in cytosolic small subunit of ADP-glucose pyrophosphorylase, reveal coordinate adjustment of C:N metabolism mediated by an overlapping metabolic-hormonal control. The Plant Journal, 69: 1077–1093. doi: 10.1111/j.1365-313X.2011.04857.x
- Issue published online: 16 MAR 2012
- Article first published online: 10 JAN 2012
- Accepted manuscript online: 18 NOV 2011 10:26AM EST
- Received 15 August 2011; revised 14 November 2011; accepted 15 November 2011; published online 10 January 2012.
- ADP-glucose pyrophosphorylase;
- endosperm development;
- storage proteins;
- metabolic regulation
The barley Risø16 mutation leads to inactivation of cytosolic ADP-Glc pyrophosphorylase, and results in decreased ADP-Glc and endospermal starch levels. Here we show that this mutation is accompanied by a decrease in storage protein accumulation and seed size, which indicates that alteration of a single enzymatic step can change the network of storage metabolism as a whole. We used comprehensive transcript, metabolite and hormonal profiling to compare grain metabolism and development of Risø16 and wild-type endosperm. Despite increased sugar availability in mutant endosperm, glycolytic intermediates downstream of hexose phosphates remained unchanged or decreased, while several glycolytic enzymes were downregulated at the transcriptional level. Metabolite and transcript profiling also indicated an inhibition of the tricarboxylic acid cycle at the level of mitochondrial nicotinamide adenine dinucleotide (NAD)-isocitrate dehydrogenase and an attendant decrease in alpha-ketoglutarate and amino acids levels in Risø16, compared with wild type. Decreased levels of cytokinins in Risø16 endosperm suggested co-regulation between starch synthesis, abscisic acid (ABA) deficiency and cytokinin biosynthesis. Comparative cis-element analysis in promoters of jointly downregulated genes in Risø16 revealed an overlap between metabolic and hormonal regulation, which leds to a coordinated downregulation of endosperm-specific and ABA-inducible gene expression (storage proteins) together with repression by sugars (isocitrate dehydrogenase, amylases). Such co-regulation ensured that decreased carbon fluxes into starch lead to a coordinated inhibition of glycolysis, amino acid and storage proteins biosynthesis, which is useful in the prevention of osmotic imbalances and oxidative stress due to increased accumulation of sugars.