Primary multistep phosphorelay activation comprises both cytokinin and abiotic stress responses in Brassicaceae

Abstract

AbstractMultistep phosphorelay (MSP) signaling integrates hormonal and environmental signals to control plant development and adaptive responses. The type-ARESPONSE REGULATORs(RRAs), the downstream members of the MSP cascade and cytokinin primary response genes, are supposed to mediate primarily the negative feedback regulation of (cytokinin-induced) MSP signaling. However, the transcriptional data suggest the involvement ofRRAsin stress-related responses as well. By employing evolutionary conservation with the well-characterizedArabidopsis thaliana RRAs, we identified 5 and 38 novel putativeRRAsinBrassica oleraceaandBrassica napus, respectively. Our phylogenetic analysis suggests the existence of gene-specific selective pressure, maintaining the homologs ofARR3, ARR6,andARR16as singletons during the evolution ofBrassica oleraceaandBrassica rapa. We categorizedRRAsbased on the kinetics of their cytokinin-mediated upregulation and observed both similarities and specificities in this type of response across Brassicaceae. Using bioinformatic analysis and experimental data demonstrating the cytokinin responsiveness ofArabidopsis-derivedTCSv2reporter, we unveil the mechanistic conservation of cytokinin-mediated upregulation ofRRAsinBrassica rapaandBrassica napus. Notably, we identify partial cytokinin dependency of cold stress-inducedRRAtranscription, thus corroborating the role of cytokinin signaling in the crop adaptive responses.HighlightsWe identifiedBrassicahomologs ofArabidopsistype-A response regulators (RRAs), demonstrate existence of selective pressure preventing severalRRAsmultiplication during Brassicaceae evolution and describe cytokinin dependency of cold-inducedRRAsupregulation.