Body of Abstract: The transition from vegetative to reproductive development (floral transition) is a costly process in annual plants requiring increased investments of metabolic resources. The Arabidopsis thaliana PHD finger protein EDM2 and RRM domain proteins EDM3 and IBM2 form chromatin-associated complexes controlling gene expression. We found distinct splice isoforms of EDM3 and IBM2 cooperate in the coordination of the floral transition with basal immune responses. These cooperating splice isoforms, termed EDM3L and IBM2L, control the intensity of basal immunity and, via a separate pathway, the timing of the floral transition. During the developmental phase prior to the floral transition expression of all EDM3 and IBM2 isoforms gradually increases, while the EDM3L and IBM2L isoforms simultaneously down-regulate expression of the floral suppressor gene FLC and promote the transition to reproductive growth. During the same time interval these EDM3 and IBM2 splice isoforms gradually suppress basal immunity against the virulent Noco2 isolate of the pathogenic oomycete Hyaloperonospora arabidopsidis and down-regulate expression of a set of defense-associated genes and immune receptor genes. We are providing clear evidence for a dynamic process coordinating in the annual plant Arabidopsis thaliana two processes competing for metabolic resources, the transition from vegetative to reproductive growth and basal immunity.