Integrating flowering and stress responses in Arabidopsis through KH-domain genes

Plant reproductive success largely relies on flowering under favorable conditions. However, stress factors have forced plants to acquire adaptive strategies to coordinate floral timing and stress responses through key genetic elements. RNA-binding proteins with K-homology (KH) domains are emerging as versatile regulators of an increasing number of plant developmental processes, including flowering and stress acclimation. In Arabidopsis thaliana, FLK and HOS5 encode multifaceted KH-domain proteins associated with transcription and cotranscriptional operations. FLK facilitates floral transition by repressing FLC, the central flowering inhibitor, while both KH-genes have been involved in abiotic stress and defense against pathogens. Our genetic and molecular data identify HOS5 as a novel flowering regulator that, together with FLK, represses FLC. Our transcriptomics results reveal that, in addition, FLK and HOS5 cooperatively repress numerous stress-responsive genes. Consistent with this, flk hos5 double mutant plants exhibit elevated levels of stress-induced gene activities and enhanced resistance to abiotic stress and pathogenic fungi. The coordinated repression of FLC and stress-induced genes by FLK and HOS5 suggests that these KH proteins are part of a cotranscriptional regulatory hub key for orchestrating flowering time and environmental adaptation responses.