Reticulate leaves and stunted roots are independent phenotypes pointing at opposite roles of the phosphoenolpyruvate/phosphate translocator defective in cue1 in the plastids of both organs.
Phosphoenolpyruvate (PEP) serves not only as a high energy carbon compound in glycolysis, but it acts also as precursor for plastidial anabolic sequences like the shikimate pathway, which produces aromatic amino acids (AAA) and subsequently secondary plant products. After conversion to pyruvate, PEP can also enter de novo fatty acid biosynthesis, the synthesis of branched-chain amino acids, and the non-mevalonate way of isoprenoid production. As PEP cannot be generated by glycolysis in chloroplasts and a variety of non-green plastids, it has to be imported from the cytosol by a phosphate translocator (PT) specific for PEP (PPT). A loss of function of PPT1 in Arabidopsis thaliana results in the chlorophyll a/b binding protein underexpressed1 (cue1) mutant, which is characterized by reticulate leaves and stunted roots. Here we dissect the shoot- and root phenotypes, and also address the question whether or not long distance signaling by metabolites is involved in the perturbed mesophyll development of cue1. Reverse grafting experiments showed that the shoot- and root phenotypes develop independently from each other, ruling out long distance metabolite signaling. The leaf phenotype could be transiently modified even in mature leaves, e.g. by an inducible PPT1RNAi approach or by feeding AAA, the cytokinin trans-zeatin (tZ), or the putative signaling molecule dehydrodiconiferyl alcohol glucoside (DCG). Hormones, such as auxins, abscisic acid, gibberellic acid, ethylene, methyl jasmonate, and salicylic acid did not rescue the cue1 leaf phenotype. The low cell density1 (lcd1) mutant shares the reticulate leaf-, but not the stunted root phenotype with cue1. It could neither be rescued by AAA nor by tZ. In contrast, tZ and AAA further inhibited root growth both in cue1 and wild-type plants. Based on our results, we propose a model that PPT1 acts as a net importer of PEP into chloroplast, but as an overflow valve and hence exporter in root plastids.
Department of Botany II, Cologne Biocenter, University of Cologne Cologne, Germany ; Lophius Biosciences Regensburg, Germany.
Pia
P
Staehr
Department of Botany II, Cologne Biocenter, University of Cologne Cologne, Germany ; Quintiles GmbH Neu-Isenburg, Germany.
Tanja
T
Löttgert
Lehrstuhl für Botanik, Wissenschaftszentrum Weihenstephan, Technische Universität München Munich, Germany.
Alexander
A
Christmann
Department of Botany II, Cologne Biocenter, University of Cologne Cologne, Germany.
Stephan
S
Krueger
Institut für Biochemie der Pflanzen, Heinrich-Heine-Universität Düsseldorf Düsseldorf, Germany.
Christian
C
Rosar
Laboratory of Growth Regulators, Centre of the Region Haná for Biotechnological and Agricultural Research, Institute of Experimental Botany, Palacký University Olumouc, Czech Republic.
Jakub
J
Rolčík
Laboratory of Growth Regulators, Centre of the Region Haná for Biotechnological and Agricultural Research, Institute of Experimental Botany, Palacký University Olumouc, Czech Republic.
Ondřej
O
Novák
Laboratory of Growth Regulators, Centre of the Region Haná for Biotechnological and Agricultural Research, Institute of Experimental Botany, Palacký University Olumouc, Czech Republic.
Miroslav
M
Strnad
Department of Botany II, Cologne Biocenter, University of Cologne Cologne, Germany.
Kirsten
K
Bell
Institut für Biochemie der Pflanzen, Heinrich-Heine-Universität Düsseldorf Düsseldorf, Germany ; Cluster of Excellence on Plant Sciences Düsseldorf, Germany.
Andreas P M
AP
Weber
Department of Botany II, Cologne Biocenter, University of Cologne Cologne, Germany ; Cluster of Excellence on Plant Sciences Düsseldorf, Germany.
Ulf-Ingo
UI
Flügge
Department of Botany II, Cologne Biocenter, University of Cologne Cologne, Germany.
Rainer E
RE
Häusler
phosphate translocator; phosphoenolpyruvate; plastids; reticulate mutants; secondary metabolism