Inhibition de la bractée lors de la transition florale chez Arabidopsis thaliana ; Bract inhibition at floral transition in Arabidopsis thaliana

Continuously during their development, flowering plants produce a basic developmental unit:the phytomer. Canonical phytomers are composed of an internode and an axillary meristemsubtended by a leaf. The abrupt transition from vegetative to reproductive state remodels thecomposition of the phytomers. In most Brassicaceæ, including the model plant Arabidopsisthaliana, the reproductive phytomer looses its leaf, also called bract, producing a bractlesslateral floral meristem. However, production of flowers subtended by bracts have been reportedin specific environmental conditions, but only on the basal flowers of the inflorescence, producedduring floral transition. We show that in some natural accessions of Arabidopsis thaliana, suchbasal bract-flowers are common, yet not in the reference Col-0. Notably, in Tsu-0, bract-flowers are frequent regardless of environmental conditions. Moreover, contrary to what havebeen historically proposed, bract-flowers in Tsu-0 do not result from a conversion of branchesinto flowers. A transcriptomic analysis of shoot apices over floral transition in Tsu-0 andCol-0 reveals interesting heterochronies in the dynamic of gene expressions, although theirpotential link with bract production are still under investigation. To our knowledge, this studyfirst exposes the natural variations of transcriptomes from vegetative to flowering stages in A.thaliana. Notably, we show that gene expressions diverge the most precisely at the time offloral transition, recapitulating what have been previously described at an inter-species level.We also tried to map the genetic variations controlling bracts in Tsu-0 with both bulked F2segregant populations and Recombinants Inbred Lines. The genetic determinism of this trait iscomplex and we identified two major loci located in chromosome 1. We then crossed evidencefrom our genomic and transcriptomic data (including bract mutants) to propose some plausiblecandidate genes. From a particular case of natural variation, this study revisits the mechanismsthat ...