| During development, pattern formation is an important process by which individual cells have their position specified and interpret this positional information by undergoing a particular cell differentiation. To better understand the mechanism specifying position, I have used Arabidopsis thaliana to study genes involved in floral patterning.;perianthia (pan) was recognized mainly by its extra organ mutant phenotype, in which flowers were transformed from tetramerous, to largely pentamerous, a characteristic of flowers of ancestral plants. In addition to its function in establishing floral organ number, PAN is also involved in carpel development. PAN encodes a member of the basic region/leucine zipper class of transcription factors. In situ hybridization and immunolocalization revealed that its expression pattern is primarily correlated with floral organ initiation. The near absence of a phenotype in transgenic plants overexpressing PAN and the contrast between the broad expression of PAN and the specificity of its mutant phenotype suggest that its activity may be regulated post-translationally or by the presence of partner proteins. PAN was proposed to play a role in the switch from pentamerous to tetramerous flowers during the evolution of flower form in the mustard family.;A small gene family composed of three highly homologous genes, TOT1, TOT2, and TOT3, were isolated as potential targets of PAN by using differential display. These genes are up-regulated by PAN and encode products with similarity to a putative ABA-responsive protein. One way to elucidate the biological role of these potential target genes is to get their loss-of-function or reduction-of-function mutants. Double-strand RNA (dsRNA)-mediated gene silencing, which has been observed in a number of organisms, was successfully applied to four Arabidopsis genes, AGAMOUS, CLAVATA3, APETALA1, and PAN, with well-characterized functions in flower development. Use of dsRNA interference with TOT genes demonstrated these target genes are involved in the same pathway as PAN to specify floral organ patterning. The discovery of TOT genes reveals a possible role of ABA signal transduction in determination of floral organ number and carpel development. |
