AUTHOR=Staehr Pia , Löttgert Tanja , Christmann Alexander , Krueger Stephan , Rosar Christian , Rolčík Jakub , Novák Ondřej , Strnad Miroslav , Bell Kirsten , Weber Andreas P. M. , Flügge Ulf-Ingo , Häusler Rainer E. 

TITLE=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

JOURNAL=Frontiers in Plant Science

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2014.00126

DOI=10.3389/fpls.2014.00126

ISSN=1664-462X

ABSTRACT=<p>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 <italic>de novo</italic> 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 <italic>Arabidopsis thaliana</italic> results in the c<italic>hlorophyll a/b binding protein underexpressed1</italic> (<italic>cue1</italic>) 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 <italic>cue1</italic>. 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, <italic>e.g</italic>. by an inducible <italic>PPT1</italic>RNAi approach or by feeding AAA, the cytokinin <italic>trans</italic>-zeatin (<italic>t</italic>Z), 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 <italic>cue1</italic> leaf phenotype. The <italic>low cell density1</italic> (<italic>lcd1</italic>) mutant shares the reticulate leaf-, but not the stunted root phenotype with <italic>cue1</italic>. It could neither be rescued by AAA nor by <italic>t</italic>Z. In contrast, <italic>t</italic>Z and AAA further inhibited root growth both in <italic>cue1</italic> 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.</p>