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The Calvin-Benson cycle is not directly linked to transitory starch biosynthesis by means of phosphoglucose isomerase in plants exposed to microbial volatiles

AuthorsBahaji, Abdellatif ; Sánchez-López, Ángela María ; Li, Jun ; Baroja-Fernández, Edurne ; Muñoz Pérez, Francisco José ; Montero, Manuel ; Ovecka, Miroslav ; Pozueta Romero, Javier
Issue DateJul-2013
CitationXIII Congresso Luso-Espanhol de Fisiologia Vegetal (2013)
AbstractIt is widely considered that starch is the end-product of a pathway exclusively taking place in the chloroplast that is linked to the Calvin-Benson cycle by means of the plastidial phosphoglucose isomerase (pPGI). Genetic evidence showing that starch biosynthesis occurs solely by this pathway has been obtained with mutants impaired in pPGI (Yu et al. 2000, Niewiadomski et al. 2005). However, mounting evidence has been compiled previewing the occurrence of starch biosynthetic pathways bypassing pPGI and involving the cytosolic compartment. Studies carried out in our laboratory have shown that volatile compounds emitted by microorganisms promote accumulation of exceptionally high levels of starch in leaves and the expression of the plastidial glucose-6-phosphate/Pi translocator GPT2 (Ezquer et al. 2010, Li et al. 2011). To investigate the role of pPGI in this phenomenon, we characterized pPGI null ppgi Arabidopsis mutants cultured in the presence or absence of volatiles emitted by the plant pathogen Alternariaalternata. These studies revealed that, in the absence of fungal volatiles (FVs), ppgi leaves have reduced photosynthetic capacity and growth, delayed flowering, and accumulate 10-15% of the wild type starch, phenotypes that were reverted by the ectopic expression of pPGI. Most importantly, FVs-treated ppgi and ppgi/gpt2 leaves accumulated exceptionally high starch levels in the chloroplasts of mesophyll cells. The overall data presented in this work show that, when plants are exposed to microbial volatiles(i) the Calvin-Benson cycle is not directly linked to starch biosynthesis by means of pPGI, (ii) GPT2 does not provide cytosolic carbon to the chloroplast for its subsequent conversion into starch, and (iii) either cytosolic glucose-1-phosphate and/or ADP-glucose enter the chloroplast to be subsequently converted into starch. We propose that pPGI plays a role in providing glucose-6-phosphate to theoxidative pentose phosphate pathway in the night, but plays a minor role, if any in leaf starch biosynthesis during the light.
DescriptionTrabajo presentado en el XIII Congresso Luso-Espanhol de Fisiologia Vegetal, celebrado en Lisboa del 24 al 28 de julio de 2013.
Appears in Collections:(IDAB) Comunicaciones congresos
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