Aviezer-Hagai, K., Department of Plant Sciences, Tel Aviv University, Tel Aviv, Israel
Skovorodnikova, J., Department of Plant Sciences, Tel Aviv University, Tel Aviv, Israel
Galigniana, M., Instituto de Investigaciones Bioquimicas, Fundacion Instituto Leloir Buenos Aires, Buenos Aires, Argentina
Farchi-Pisanty, O., Department of Plant Sciences, Tel Aviv University, Tel Aviv, Israel
Maayan, E., Department of Plant Sciences, Tel Aviv University, Tel Aviv, Israel
Bocovza, S., Department of Plant Sciences, Tel Aviv University, Tel Aviv, Israel
Efrat, Y., Department of Plant Sciences, Tel Aviv University, Tel Aviv, Israel
Von Koskull-Döring, P., Institute of Molecular Bio Sciences, Goethe University, Frankfurt, Germany
Ohad, N., Department of Plant Sciences, Tel Aviv University, Tel Aviv, Israel
Breiman, A., Department of Plant Sciences, Tel Aviv University, Tel Aviv, Israel

The plant co-chaperones FK506-binding proteins (FKBPs) are peptidyl prolyl cis-trans isomerases that function in protein folding, signal transduction and chaperone activity. We report the characterization of the Arabidopsis large FKBPs ROF1 (AtFKBP62) and ROF2 (AtFKBP65) expression and protein accumulation patterns. Transgenic plants expressing ROF1 promoter fused to GUS reporter gene reveal that ROF1 expression is organ specific. High expression was observed in the vascular elements of roots, in hydathodes and trichomes of leaves and in stigma, sepals, and anthers. The tissue specificity and temporal expression of ROF1 and ROF2 show that they are developmentally regulated. Although ROF1 and ROF2 share 85% identity, their expression in response to heat stress is differentially regulated. Both genes are induced in plants exposed to 37°C, but only ROF2 is a bonafide heat-stress protein, undetected when plants are grown at 22°C. ROF1/ROF2 proteins accumulate at 37°C, remain stable for at least 4 h upon recovery at 22°C, whereas, their mRNA level is reduced after 1 h at 22°C. By protein interaction assays, it was demonstrated, that ROF1 is a novel partner of HSP90. The five amino acids identified as essential for recognition and interaction between the mammalian chaperones and HSP90 are conserved in the plant ROF1-HSP90. We suggest that ROF/HSP90 complexes assemble in vivo. We propose that specific complexes formation between an HSP90 and ROF isoforms depends on their spatial and temporal expression. Such complexes might be regulated by environmental conditions such as heat stress or internal cues such as different hormones. © 2006 Springer Science+Business Media B.V.