Molecular and functional characterization of Brassica BREVIPEDICELLUS orthologs involved in inflorescence architecture

The diversity of inflorescence architecture in angiosperms relates to attracting pollinators and allowing the effective dispersal of seeds. Molecular understanding of the genetic factors regulating inflorescence architecture from the model system of Arabidopsis could provide critical insights for addressing this developmental process/pathway in a closely related crop species like Brassica napus L. Towards this objective, we have isolated and characterized the orthologs of the homeobox gene BREVIPEDICELLUS (BP) in three Brassica species, B. napus (BnBP), Brassica rapa L. (BrBP), and Brassica oleracea L. (BoBP). These Brassica orthologs show a high degree of conservation at the nucleotide and amino acid level, including the homeodomain and the intron positions. The B. napus ortholog complemented the Arabidopsis by null allele and overexpression of BnBP in B. napus transgenic lines resulted in altered leaf phenotypes. Together, these results suggest that Brassica BP genes are functional orthologs of Arabidopsis BP. Ectopic expression of AS2, a negative regulator of BP encoding a LOB domain transcription factor, in transgenic B. napus produced compact inflorescence architecture reminiscent of the loss-of-function by mutant phenotype described previously in Arabidopsis. These results provide evidence in support of BP as a potential target gene for modifying inflorescence architecture in Brassica crop species. Key words: architecture, ASYMMETRIC LEAVES2, Brassica, BREVIPEDICELLUS, homeobox genes, inflorescence. La diversite de l'architecture des inflorescences chez les angiospermes a des effets sur l'attraction des pollinisateurs et permet une bonne dispersion des graines. La comprehension moleculaire des facteurs genetiques reglant l'architecture des inflorescences a partir de l'Arabidopsis pourrait offrir un apercu critique pour etudier ce processus/sentier du developpement, chez une espece cultivee tres voisine comme le Brassica napus L. A cet effet, les auteurs ont isole et caracterise les orthologues du gene de la sequence homeotique BREVIPEDICELLUS (BP) chez trois especes de Brassica: B. napus (BnBP), Brassica rapa L. (BrBP) et Brassica oleracea L. (BoBP). Ces orthologues de Brassica montrent une importante conservation a l'echelle des nucleotides et des acides amines, incluant l'homeodomaine et les positions des introus. L'orthologue du B. napus complemente l'allele nul hp de l'Arabidopsis et on observe une surexpression du BnBP chez les lignees transgeniques du B. napus, conduisant a des phenotypes aux feuilles modifiees. Pris dans leur ensemble, ces resultats suggerent que les genes Brassica BP constituent des orthologues fonctionnels de 'Arabidopsis BP. L'expression ectopique du AS2, un regulateur negatif des BP codant pour un facteur de transcription du domaine LOB chez le B. napus produit une inflorescence compacte rappelant le phenotype mutant de perte de fonction hp, deja decrit chez l'Arabidopsis. Ces resultats demontrent que la BP constitue un gene cible potentiel pour la modification de l'architecture florale chez les especes cultivees de Brassica. Mots-cles: aechitecture, ASYMMMETRIC LEAVES2, Brassica, BREVIPEDICELLUS, gene de sequence homeotique, inflorescence. [Traduit par la Redaction]
Introduction The body plan in animals is laid out during embryogenesis and is elaborated during growth and development. In plants, although the apical and basal polarity of the body plan [...]