Functional characterization of a novel transport protein regulating cytokinin activity in plants

• Applicant: Professor Dr. Tomás Werner
• Subject Area: Plant Cell and Developmental Biology
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 239463989

The phytohormone cytokinin is an important regulator of plant growth and the major steps of its metabolism and signal transduction have been disclosed in recent years. Other regulatory mechanisms involved in cytokinin functioning are yet to be discovered. Cytokinin deficiency causes complex phenotypic alterations such as retarded shoot and enhanced root growth. In order to uncover new elements required for the proper activity of the cytokinin system, we previously screened for suppressor alleles that reverse the shoot development of cytokinin-deficient 35S:CKX1 transgenic Arabidopsis plants. The isolated recessive mutant allele rock1 (repressor of cytokinin deficiency 1) is effectively suppressing cytokinin deficiency caused by overexpression of different CKX isoforms. ROCK1 encodes an as yet uncharacterized putative membrane transport protein with a low sequence homology to nucleotide-sugar transporters. This gene has presumably no paralogs in Arabidopsis. ROCK1-GFP fusion protein is retained in the endoplasmic reticulum by a C-terminal dilysine motif. A strong overexpression causes lethality during the early seedling stage. The cytokinin metabolism was changed in rock1 and ROCK1-overexpressing plants, suggesting a role of ROCK1 in cellular cytokinin homeostasis. The first goal of this project is to decipher the cellular function of ROCK1 protein and to identify its transport substrate(s). The second goal is to unravel the genetic context of ROCK1 activity by isolating second-site suppressor alleles of rock1. To this end, we performed a phenotype-based forward genetic screen for Arabidopsis mutants that lost the repressing rock1-activity on the cytokinin deficiency in 35S:CKX1 plants. The isolated mutant candidates will be closely characterized and the respective causal sequence variants identified by mapping.

• DFG Programme: Research Grants