Abstract
For better understanding of position-dependent growth process, novel Arabidopsis ibo mutants exhibiting ectopic tip growth in hypocotyl epidermal cells were isolated. Hypocotyl epidermal cells in ibo1 underwent ectopic tip growth at the center of the cell to form a protrusion reminiscent of root hair. Similar ectopic protrusions were observed in epidermal cells in petioles and midribs of ibo1. ibo1 mutations had no adverse effects on differentiation patterns of root hairs, stomata, and trichomes. ibo1 exhibited normal expression pattern of GL2, CPC, and SHV3 family. Ectopic tip growth in ibo1 was preferentially induced in non-stomatal cell files expressing GL2 and CPC. Ectopic tip growth in ibo1 was reduced by the application of ethylene-biosynthesis inhibitor, and restored by the ethylene precursor. cpc-1 ibo1 double mutants exhibited additive phenotypes; ectopic protrusions in hypocotyls and reduced root hair formation. Possible function of IBO1 in the suppression of ectopic tip growth will be discussed.
