MUTATION IN THE ARABIDOPSIS PASTICCINO1 GENE, WHICH ENCODES A NEW FK506-BINDING PROTEIN-LIKE PROTEIN, HAS A DRAMATIC EFFECT ON PLANT DEVELOPMENT

The pasticcino (pas) mutants of Arabidopsis thaliana are a new class o f plant developmental mutants; members of this class show ectopic cell proliferation in cotyledons, extra layers of cells in the hypocotyl, and an abnormal apical meristem. This phenotype is correlated with bot h cell division and cell elongation defects. There are three complemen tation groups of pas mutants (pas1, pas2, and pas3, with, respectively 2, 1, and 4 alleles), Here we describe in more detail the pas1-1 alle le, which was obtained by insertional mutagenesis. The PAS1 gene has b een cloned and characterized; it encodes an immunophilin-like protein similar to the p59 FK506-binding protein (FKBP52). PAS1 is characteriz ed by an FKBP-like domain and three tetratricopeptide repeat units. Al though the presence of immunophilins in plants has already been demons trated, the pas1-1 mutant represents the first inactivation of an FKBP -like gene in plants. PAS1 expression is altered in pas1 mutants and i n the pas2 and pas3 mutants. The expression of the PAS1 gene is increa sed in the presence of cytokinins, a class of phytohormones originally discovered because of their ability to stimulate cell division. These results are of particular relevance as they show for the first time t hat an FKBP-like protein plays an important role in the control of pla nt development.