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Published on February 20, 2008; 10.1104/pp.107.112698

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Received November 6, 2007
Accepted February 15, 2008

Transcriptional and metabolic adjustments in AGPase deficient bt2 maize kernels

Magalie Cossegal , Pierre Chambrier , Sylvie Mbelo , Sandrine Balzergue , Marie-Laure Martin-Magniette , Annick Moing , Catherine Deborde , Virginie Guyon , Pascual Perez , and Peter Rogowsky *

RDP, UMR 5667 INRA-CNRS-ENSL-UCBL, IFR128 BioSciences Lyon-Gerland, ENS-Lyon, 46 Allee d'Italie, F-69364 Lyon Cedex 07, France; URGV, UMR1165 INRA-CNRS-UEVE, 2 rue Gaston Cremieux, F-91057 Evry Cedex, France; Pole Metabolome de la Plateforme Genomique Fonctionnelle Bordeaux, IFR BVI, BP 81, F-33883 Villenave d'Ornon, France; Biogemma SAS, Laboratoire de Biologie Cellulaire et Moleculaire, 8 rue des freres Lumiere, F-63028 Clermont-Ferrand Cedex 2, France; INRA UMR AgroParisTech/INRA MIA 518, 16 rue Claude Bernard, F-75231 Paris Cedex 05, France

* Corresponding author; email: peter.rogowsky{at}ens-lyon.fr.

During the cloning of monogenic recessive mutations responsible for defective kernel phenotypes in a Mutator induced maize 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. RT-PCR 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, while 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 days after pollination (DAP) mutant kernels were plumper than wildtype ones, 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 wildtype and bt2-H2328 kernels at mid-development (35 DAP) with the 18K GeneChip® Maize Genome Array led 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 (PCA) of 1H-NMR metabolic profiles confirmed the impact of the bt2-H2328 mutation on these pathways and revealed that the bt2-H2328 mutation did not affect exclusively 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).




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T. L. Slewinski, Y. Ma, R. F. Baker, M. Huang, R. Meeley, and D. M. Braun
Determining the Role of Tie-dyed1 in Starch Metabolism: Epistasis Analysis with a Maize ADP-Glucose Pyrophosphorylase Mutant Lacking Leaf Starch
J. Hered., August 22, 2008; (2008) esn062v1.
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