Characterization of root cells of anl2 mutant in Arabidopsis thaliana.

A mutation in the ANTHOCYANINLESS2 (ANL2) gene of Arabidopsis thaliana causes the formation of several extra cells called intervening cells (IV cells) between the cortical and epidermal layers of the primary root. The origin and character of IV cells were examined. Microscopic observation of serial sections of the root tissue showed that IV cells developed from epidermal cells, and the outer cells overlying the epidermal cells developed into epidermal-like cells. The IV cells expressed the marker gene for cortical cells, which indicated that the IV cells were cortical in nature. IV cells were primarily observed in a cleft between two cortical cells or between a cortical and an IV cell, which suggests the involvement of positional information between cortical and epidermal cells. Ectopic root hairs were formed, and the expression patterns of β-glucuronidase driven by the GL2 and CPC promoters were irregular in the primary root of the anl2 mutant. These results indicate that ANL2 is required for the maintenance of epidermal cell lineage.