Auxin export from proximal fruits drives arrest in competent inflorescence meristems

A well-defined set of regulatory pathways control entry into the reproductive phase in flowering plants. Conversely, little is known about the mechanisms that control the end of the reproductive phase (floral arrest), despite this being a critical process for optimising fruit and seed production. Complete fruit removal or lack of fertile fruit-set in male sterile mutants, for example male sterile1 (ms1), prevents timely floral arrest in the model plant Arabidopsis. These observations formed the basis for Hensel and colleagues model in which end-of-flowering was proposed to result from a cumulative fruit/seed-derived signal that caused simultaneous global proliferative arrest (GPA) in all inflorescences. Recent studies have suggested that end-of-flowering involves gene expression changes at the floral meristem which are at least in part controlled by the FRUITFULL-APETELA2 pathway, however there is limited understanding of how this process is controlled and the communication needed at the whole plant level. Here, we provide new information providing a framework for the fruit-to-meristem (F-M) communication implied by the GPA model. We show that floral arrest in Arabidopsis is not global and does not occur synchronously between branches, but rather that the arrest of each inflorescence is a local process, driven by auxin export from fruit proximal to the inflorescence meristem (IM). Furthermore, we show that inflorescence meristems are only competent for floral arrest once they reach a certain developmental age. Understanding the regulation of floral arrest is of major importance for the future manipulation of flowering to extend and maximise crop yields.