Understanding how plants adapt to stressing conditions, and what the genetic bases of this adaptation are, is essential to accurately predict plant behaviors in response to environmental changes. Plants in nature and crop fields are simultaneously exposed to numerous environmental stresses that could exert significant selection. As a consequence, plants have adapted their development to a remarkable large range of environmental conditions including biotic and abiotic stresses. Preserving plant growth and development in the climatic change context is a real challenge. It is well-established that a large part of plant development plasticity is related to changes in cell cycle activity, as shown by robust relationships between organ size and their cell number in different species and many environmental scenarios. Identification of the molecular basis controlling cell cycle plasticity could foster a better understanding of how plants respond to their environment. In addition, it could be a potential source of adaptation to stressing conditions by manipulating cell cycle regulation. The molecular network acting at the G1-to-S cell cycle transition is reported as a crucial limiting factor when cell cycle is lengthened by environmental stresses. Abiotic stresses induce the expression of cyclin-dependent kinase inhibitors (CKI) that reduce cyclin-dependent kinase (CDK) activities, reduce cell proliferation and thus, plant growth. In the CKI-stress project, we will focus on this family of genes mainly because some of them have previously been identified as major control of the cell cycle progression in response to stresses. Several complementary genetic and molecular approaches will be combined with the aim to allow a better understanding of the plant CKI role and function in plant stress responses. In particular we will focus our work on salt, drought and temperature stresses. Arabidopsis will be used as a model system to take advantage of available or potential genetic material as well as an automated platform for reproducible phenotyping of plant responses to stress. Multiple loss-of-function mutants affected on KRPs and SIM-related members known to be stress-induced will be subjected to abiotic stress conditions and analysed with a multi-scale phenotyping approach from cellular processes (cell division, endoreduplication…) to whole plant regulation (leaf expansion, floral transition…). These phenotypical analyses will be completed by molecular and biochemical approaches to reveal post-translational regulations on SIM/SMRs in stress responses, including “degron” mapping of selected SIM/SMRs and the identification of novel E3s involved in SIM/SMRs turnover. Thus we aim to identify all members of the SIM/SMR family involved in these abiotic stress responses. Moreover, we will investigate how these genes are regulated by the gibberellin-regulated DELLA proteins and also by ABA or other stress hormones that impact on cell proliferation.