Pause-and-stop: The effects of osmotic stress on cell proliferation during early leaf development in Arabidopsis and a role for ethylene signaling in cell cycle arrest

Despite its relevance for agricultural production, environmental stress-induced growth inhibition, which is responsible for-significant yield reductions, is only poorly understood. Here, we investigated the molecular mechanisms underlying cell-cycle inhibition in young proliferating leaves of the model plant Arabidopsis thaliana when subjected to mild osmotic stress. A detailed cellular analysis demonstrated that as soon as osmotic stress is sensed, cell cycle progression rapidly arrests,-but cells are kept in a latent ambivalent state allowing a quick recovery (pause). Remarkably, cell cycle arrest coincides with-an increase in 1-aminocyclopropane-1-carboxylate levels and the activation of ethylene signaling. Our work showed that-ethylene acts on cell cycle progression via inhibition of cyclin-dependent kinase A activity independently of EIN3 transcriptional-control. When the stress persists, cells exit the mitotic cell cycle and initiate the differentiation process (stop).-This stop is reflected by early endore duplication onset, in a process independent of ethylene. Nonetheless, the potential to-partially recover the decreased cell numbers remains due to the activity of meristemoids. Together, these data present a-conceptual framework to understand how environmental stress reduces plant growth.