Starch Granule Initiation in Arabidopsis Requires the Presence of Either Class IV or Class III Starch Synthases.
Szydlowski, Nicolas | Ragel, Paula | Raynaud, Sandy | Lucas, M Mercedes | Roldán, Isaac | Montero, Manuel | Muñoz, Francisco José | Ovecka, Miroslav | Bahaji, Abdellatif | Planchot, Véronique | Pozueta-Romero, Javier | d'Hulst, Christophe | Mérida, Angel | Unité de Glycobiologie Structurale et Fonctionnelle UMR 8576 (UGSF) ; Université de Lille-Centre National de la Recherche Scientifique (CNRS) | Instituto de Bioquimica Vegetal y Fotosintesis (IBVF) ; Consejo Superior de Investigaciones Cientificas = Spanish National Research Council (CSIC) | Unité de recherche sur les Biopolymères, Interactions Assemblages (BIA) ; Institut National de la Recherche Agronomique (INRA)
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Показать больше [+] Меньше [-]Английский. The mechanisms underlying starch granule initiation remain unknown. We have recently reported that mutation of soluble starch synthase IV (SSIV) in Arabidopsis thaliana results in restriction of the number of starch granules to a single, large, particle per plastid, thereby defining an important component of the starch priming machinery. In this work, we provide further evidence for the function of SSIV in the priming process of starch granule formation and show that SSIV is necessary and sufficient to establish the correct number of starch granules observed in wild-type chloroplasts. The role of SSIV in granule seeding can be replaced, in part, by the phylogenetically related SSIII. Indeed, the simultaneous elimination of both proteins prevents Arabidopsis from synthesizing starch, thus demonstrating that other starch synthases cannot support starch synthesis despite remaining enzymatically active. Herein, we describe the substrate specificity and kinetic properties of SSIV and its subchloroplastic localization in specific regions associated with the edges of starch granules. The data presented in this work point to a complex mechanism for starch granule formation and to the different abilities of SSIV and SSIII to support this process in Arabidopsis leaves.
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