Abstract
To identify new regulator of cellular morphogenesis, we isolated loss-of-function mutants of Arabidopsis thaliana, ibo1. The ibo1 mutations caused local outgrowth in the middle of hypocotyl epidermal cells, resulting in the formation of a protuberance reminiscent in appearance of a root hair. The protuberances in ibo1 were preferentially induced in the non-stoma cell files. Double mutant analysis indicated that TTG1-dependent epidermal patterning is required for protuberance formation in ibo1, suggesting IBO1 functions downstream of epidermal cell specification. Pharmacological and genetic analysis demonstrated that ethylene promotes protuberance formation in ibo1, implying that IBO1 acts antagonistically with ethylene to suppress radial outgrowth. IBO1 encodes a NIMA-related protein kinase. The ibo1-1 mutation completely abolished kinase activity of IBO1. Intracellular localization of IBO1 showed that IBO1 associated with cortical microtubules. These results suggest that IBO1 suppresses ectopic outgrowth in epidermal cells through the organization of microtubules.
