Mosaic analysis of GL2 gene expression and cell layer autonomy during the specification of Arabidopsis leaf trichomes.

Homozygous glabra2 (gl2) mutant Arabidopsis thaliana Landsberg erecta plants with only a few rudimentary single spiked trichomes on the leaf margin were transformed with a genomic clone of GL2, resulting in partial restoration of the normal leaf trichome phenotype. The introduced GL2 transgene was configured as part of an FLP recombinase-responsive gene switch, which permitted visibly marked gl2 mutant clonal sectors to be generated by FLP recombinase-mediated deletion of the GL2 transgene with concomitant activation of a previously silent beta-glucuronidase (GUS) marker gene. GUS marked sectors extending through all three leaf cell layers (L1, L2, and L3) displayed the anticipated gl2 mutant phenotype, whereas immediately adjacent unmarked tissue, and unmarked tissues overlaying GUS sectors restricted to the L2 and/or L3 cell layers, retained the GL2 restored phenotype. These data support the view that the GL2 gene product acts in a region-autonomous manner within a single cell layer and indicate that GL2 gene expression in the L1 layer is sufficient for GL2-directed outgrowth of trichomes.