PASTICCINO1 (AtFKBP70) is a nuclear-localised immunophilin required duringArabidopsis thaliana embryogenesis

The PASTICCINO1 (PAS1) gene of Arabidopsis thaliana encodes a protein with homology to the FK506-binding protein (FKBP) class of immunophilins. To beg in to understand more about the possible function of PAS1, we tested some p roperties of recombinant PAS1 protein and analysed the expression of the ge ne in Arabidopsis embryos and cell cultures and in tobacco cells. In pas1-1 /+ heterozygote embryos the pas1-1 allele is expressed at very low levels i n all cells, but it is misexpressed in the pas1-1 homozygote mutant at the same stage. Anti-PAS1 affinity-purified antibodies recognise a 70 kDa prote in from dividing cell cultures of Arabidopsis. In indirect immunofluorescen ce, the same antibodies label the nuclei of dividing tobacco BY-2 cells. In a protease-coupled assay, recombinant PAS1 protein has low peptidylprolyl cis-trans isomerase (PPIase) activity, which is inhibited by the immunosupp ressive drugs FK506 and rapamycin, but not by cyclosporin. PAS1 also binds calmodulin in vitro. This data suggests the importance of the correctly reg ulated production of functional PAS1 protein, a likely nuclear-localised FK BP, for the correct development of the plant embryo. (C) 2001 Elsevier Scie nce Ireland Ltd. All rights reserved.