Du gène à la fleur

National audienceAu-delà de l'expérimentation in vitro, l'expérimentation sur ordinateur devrait permettre de mieux comprendre les conditions de croissance des plantes

Floral stem cell termination involves the direct regulation of AGAMOUS by PERIANTHIA

In Arabidopsis, the population of stem cells present in young flower buds is lost after the production of a fixed number of floral organs. The precisely timed repression of the stem cell identity gene WUSCHEL (WUS) by the floral homeotic protein AGAMOUS (AG) is a key part of this process. In this study, we report on the identification of a novel input into the process of floral stem cell regulation. We use genetics and chromatin immunoprecipitation assays to demonstrate that the bZIP transcription factor PERIANTHIA (PAN) plays a role in regulating stem cell fate by directly controlling AG expression and suggest that this activity is spatially restricted to the centermost region of the AG expression domain. These results suggest that the termination of floral stem cell fate is a multiply redundant process involving loci with unrelated floral patterning functions

Using mechanics in the modelling of meristem morphogenesis

International audienceno abstrac

Flux-Based Transport Enhancement as a Plausible Unifying Mechanism for Auxin Transport in Meristem Development

Plants continuously generate new organs through the activity of populations of stem cells called meristems. The shoot apical meristem initiates leaves, flowers, and lateral meristems in highly ordered, spiralled, or whorled patterns via a process called phyllotaxis. It is commonly accepted that the active transport of the plant hormone auxin plays a major role in this process. Current hypotheses propose that cellular hormone transporters of the PIN family would create local auxin maxima at precise positions, which in turn would lead to organ initiation. To explain how auxin transporters could create hormone fluxes to distinct regions within the plant, different concepts have been proposed. A major hypothesis, canalization, proposes that the auxin transporters act by amplifying and stabilizing existing fluxes, which could be initiated, for example, by local diffusion. This convincingly explains the organised auxin fluxes during vein formation, but for the shoot apical meristem a second hypothesis was proposed, where the hormone would be systematically transported towards the areas with the highest concentrations. This implies the coexistence of two radically different mechanisms for PIN allocation in the membrane, one based on flux sensing and the other on local concentration sensing. Because these patterning processes require the interaction of hundreds of cells, it is impossible to estimate on a purely intuitive basis if a particular scenario is plausible or not. Therefore, computational modelling provides a powerful means to test this type of complex hypothesis. Here, using a dedicated computer simulation tool, we show that a flux-based polarization hypothesis is able to explain auxin transport at the shoot meristem as well, thus providing a unifying concept for the control of auxin distribution in the plant. Further experiments are now required to distinguish between flux-based polarization and other hypotheses