Characterization of TCP genes in Arabidopsis thaliana

TCP genes comprise a large family of genes that have been implicated in a diverse range of plant developmental pathways ranging from lateral branching (Doebley et al, 1997) to organ symmetry (Luo et al, 1999) and leaf curvature (Nath et al, 2003; Palatnik et al, 2003). I studied three closely related Arabidopsis TCP genes, one of which was recovered in an enhancer trap screen to identify downstream targets of the regulator of inflorescence architecture, BREVIPEDICELLUS (Douglas and Riggs, 2005). The enhancer trap marker line served as a reporter for TCP15 expression. Data mining has revealed a possible link between TCP15 and the hormone auxin. Using the DR5::GUS molecular reporter for auxin accumulation I found that TCP15 and the related TCP14 genes limit auxin maxima in seedling and reproductive tissues and that auxin transport is necessary for correct TCP15 expression. The closely related TCP8 gene was found to regulate leaf shape as demonstrated by decreased leaf index values. The rounder leaves of tcp8 plants also exhibited increased adaxial trichome and stomatal densities resulting in significantly decreased spacing between adjacent cells. tcp8 leaves showed increased serration density suggesting that TCP8 limits marginal outgrowth. Vein patterning was also perturbed in the mutants. Vein loops were rounder and smaller, and decreased loop subdivision indicated that vein patterning is retarded in the mutant. TCP8 evokes organ-specific effects on vascular patterning as mutant rosette leaves showed increased vascular complexity, whereas mutant cauline leaves showed decreased vein complexity. These results suggest that TCP8 is necessary for correct leaf development. The Arabidopsis genome contains 24 TCP genes, many of which have not been characterized. Studies of these genes will lead to the identification of additional factors necessary to control plant architecture and enable us to optimize plant growth and yield using genetic engineering.Ph