Studies on the Physiological Function of Rice Cytokinin Response Regulators OsRR6 and OsRR11

Cytokinins are plant hormones that play important regulatory roles in plant developmental and physiological processes. Cytokinin signaling pathway is a multistep His-Asp phosphorelay system known as the two-component system. The type-A response regulator genes in Arabidopsis and rice are rapidly induced by exogenous cytokinin and have been characterized as cytokinin primary response genes. Some of type-A RRs in Arabidopsis and rice act as negative regulators of cytokinin responses by a feedback mechanism. It has been known that there are thirteen type-A RRs in rice and may perform partially redundant functions. Based on the phylogenetic relationship and tissue specificity, in this study, I characterized the functions of OsRR6 and OsRR11, using CRISPR/Cas9 gene-editing approach to establish Osrr6/11 mutants. Mutation rate of Osrr6/11 mutants are over 80% and mainly occurring in 1 bp deletion. Real-time qPCR analysis indicated that OsRR6 exhibits high expression and is expressed in all organs; while OsRR11 exhibits very low expression and is expressed only in the shoot. Besides, OsRR6 can be up-regulated by high temperature and drought stresses; while OsRR11 can be down-regulated by salinity and drought stresses. These results illustrated that OsRR6 and OsRR11 participate in plant responses to different stresses and may have different functions under abiotic stresses. In order to gain insight into their functions, we conduct cytokinin response analysis by using Osrr6/11 mutants. Compared to WT, Osrr6/11 mutants have more adventitious roots, delay leaf senescence and promote callus shoot regeneration. Taken together, these data suggested that OsRR6 and OsRR11 play negative role in cytokinin signaling transduction.