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Characterization of the phosphoenolpyruvate carboxylase gene family in grasses (Poaceae)

Besnard G., Pinçon G., D'Hont A., Robert C., Rondeau P., Hoarau J.Y., Offmann B.G., Rouch C., Cadet F.. 2003. In : IVth Molecular biology workshop, Montpellier, France, 7-11 April 2003 [Abstracts]. Montpellier : CIRAD-CA, p. 2-2. Molecular Biology Workshop. 4, 2003-04-07/2003-04-11, Montpellier (France).

Phosphoenolpyruvate carboxylases (PEPCs) are encoded by an oligogenic family. A few isoforms have been described in grasses, mainly in sorghum and maize. One of them (C4 PEPC) is involved in the C4 photosynthetic pathway. In order to characterize the PEPC gene family in grasses, DNA fragments encoding PEPCs were isolated on a representative sample Of C4 grasses using PCR-based cloning. A phylogenetic study revealed the existence of four main PEPC gene lineages in grasses and particularly in sugarcane. Moreover this analysis suggests that grass C4 PEPC has likely derived from a root pre-existing isoform in an ancestral species. Moreover, in the phylogenetic tree, C4 PEPC genes gathered in only one clade and species relationships deduced from this isoform were similar to those described using orthologous nuclear or chloroplastic genes. This suggests that the C4 isoform should have appeared only once during grass evolution. According our data, the hypothesis of multiple C4 photosynthesis appearances in Poaceae is then challenged. Using the Northerndot-blot method, we studied the expression of the four PEPC gene classes in the sugarcane cultivar R570. We confirmed that transcript accumulation of the C4 PEPC gene (ppc-C4) mainly occurs in green leaves and is light induced. We also showed that another member (ppc-aR) is more highly transcribed in roots. The constitutive expression for a previously characterized gene (ppc-aL2) was confirmed. Lastly, transcript accumulation of the fourth PEPC gene class (ppc-aL1) was not revealed. Length polymorphism in non coding regions for three PEPC gene lineages enabled us to develop STS PEPC markers in sugarcane. We analyzed the segregation of PEPC fragments in R570 self-pollinated progenies. We revealed co-segregating fragments for two PEPC gene lineages. Our results supported that diversification of PEPC genes should have been associated to polyploidization events but also to duplications probably in tandem. (Texte intégral)

Mots-clés : poaceae; phosphoenolpyruvate carboxylase; gène; identification

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