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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Transcriptional and Metabolic Adjustments in ADP-Glucose Pyrophosphorylase-Deficient bt2 Maize Kernels^1,[W]

Reproduction et Développement des Plantes, UMR 879 INRA-CNRS-ENSL-UCBL, IFR128 BioSciences Lyon-Gerland, F–69364 Lyon cedex 07, France (M.C., P.C., S.M., P.R.); Unité de Recherche en Génomique Végétale, UMR 1165 INRA-CNRS-UEVE, F–91057 Evry cedex, France (S.B., M.-L.M.-M.); Pôle Métabolome de la Plateforme Génomique Fonctionnelle Bordeaux, IFR BVI, F–33883 Villenave d'Ornon, France (A.M., C.D.); Biogemma SAS, Laboratoire de Biologie Cellulaire et Moléculaire, F–63028 Clermont-Ferrand cedex 2, France (V.G., P.P.); and INRA UMR AgroParisTech/INRA MIA, F–75231 Paris cedex 05, France (M.-L.M.-M.)

During the cloning of monogenic recessive mutations responsible for a defective kernel phenotype in a Mutator-induced Zea mays mutant collection, we isolated a new mutant allele in Brittle2 (Bt2), which codes for the small subunit of ADP-glucose pyrophosphorylase (AGPase), a key enzyme in starch synthesis. Reverse transcription-polymerase chain reaction experiments with gene-specific primers confirmed a predominant expression of Bt2 in endosperm, of Agpsemzm in embryo, and of Agpslzm in leaf, but also revealed considerable additional expression in various tissues for all three genes. Bt2a, the classical transcript coding for a cytoplasmic isoform, was almost exclusively expressed in the developing endosperm, whereas Bt2b, an alternative transcript coding for a plastidial isoform, was expressed in almost all tissues tested with a pattern very similar to that of Agpslzm. The phenotypic analysis showed that, at 30 d after pollination (DAP), mutant kernels were plumper than wild-type kernels, that the onset of kernel collapse took place between 31 and 35 DAP, and that the number of starch grains was greatly reduced in the mutant endosperm but not the mutant embryo. A comparative transcriptome analysis of wild-type and bt2-H2328 kernels at middevelopment (35 DAP) with the 18K GeneChip Maize Genome Array led to the conclusion that the lack of Bt2-encoded AGPase triggers large-scale changes on the transcriptional level that concern mainly genes involved in carbohydrate or amino acid metabolic pathways. Principal component analysis of ¹H nuclear magnetic resonance metabolic profiles confirmed the impact of the bt2-H2328 mutation on these pathways and revealed that the bt2-H2328 mutation did not only affect the endosperm, but also the embryo at the metabolic level. These data suggest that, in the bt2-H2328 endosperms, regulatory networks are activated that redirect excess carbon into alternative biosynthetic pathways (amino acid synthesis) or into other tissues (embryo).

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Peter Rogowsky (peter.rogowsky{at}ens-lyon.fr).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.112698

^* Corresponding author; e-mail peter.rogowsky{at}ens-lyon.fr.

Received November 6, 2007; accepted February 15, 2008; published February 20, 2008.

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