Abstract
After a vegetative phase, plants initiate the floral transition in response to both environmental and endogenous cues to optimize reproductive success. During this process, the vegetative shoot apical meristem (SAM), which was producing leaves and branches, becomes an inflorescence SAM and starts producing flowers. Inflorescences can be classified in two main categories, depending on the fate of the inflorescence meristem: determinate or indeterminate. In determinate inflorescences, the SAM differentiates directly, or after the production of a certain number of flowers, into a flower, while in indeterminate inflorescences the SAM remains indeterminate and produces continuously new flowers. Even though indeterminate inflorescences have an undifferentiated SAM, the number of flowers produced by a plant is not indefinite and is characteristic of each species, indicating that it is under genetic control. In Arabidopsis thaliana and other species with indeterminate inflorescences, the end of flower production occurs by a regulated proliferative arrest of inflorescence meristems on all reproductive branches that is reminiscent of a state of induced dormancy and does not involve the determination of the SAM. This process is controlled genetically by the FRUITFULL-APETALA2 (FUL-AP2) pathway and by a correlative control exerted by the seeds through a mechanism not well understood yet. In the absence of seeds, meristem proliferative arrest does not occur, and the SAM remains actively producing flowers until it becomes determinate, differentiating into a terminal floral structure. Here we show that the indeterminate growth habit of Arabidopsis inflorescences is a facultative condition imposed by the meristematic arrest directed by FUL and the correlative signal of seeds. The terminal differentiation of the SAM when seed production is absent correlates with the induction of AGAMOUS expression in the SAM. Moreover, terminal flower formation is strictly dependent on the activity of FUL, as it was never observed in ful mutants, regardless of the fertility of the plant or the presence/absence of the AG repression exerted by APETALA2 related factors.
Highlights
IntroductionReproductive success depends on the ability to produce seeds that ensure the perpetuation of the species
For most plants, reproductive success depends on the ability to produce seeds that ensure the perpetuation of the species
As the FUL-AP2 pathway genetically controls the length of the flowering phase, we decided to assess if the FUL-AP2 module had a role in the determination of the fate of the inflorescence meristem and the formation of the terminal structure
Summary
Reproductive success depends on the ability to produce seeds that ensure the perpetuation of the species. Seed production is related to the number of flowers produced by the plant during the reproductive phase, and dependent on the activity of the inflorescence meristems that produce the flowers. Inflorescences have been classified in two major categories based on the fate of the inflorescence meristem: determinate or indeterminate Determinate inflorescences are those where the shoot apical meristem (SAM) differentiates directly, or after the production of a certain number of flowers, into a flower. The end of the reproductive phase in determinate inflorescences is established by the final differentiation of the inflorescence SAM, determining the final number of flowers and seeds produced per shoot. The length of the reproductive phase and the number of flowers produced by indeterminate inflorescences is finite, despite the undifferentiated nature of the SAM, which does not produce any terminal structure. In indeterminate inflorescences, the number of flowers produced before SAM arrest is usually distinctive for each species and/or ecotype, suggesting a genetic control of the length of the reproductive phase
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