The expression of the large rice FK506 binding proteins (FKBPs) demonstrate tissue specificity and heat stress responsiveness

The FK506 binding proteins (FKBPs) are abundant and ubiquitous proteins belonging to the large peptidyl prolyl cis-trans isomerase superfamily. In this study we have identified and characterized the expression of three large FKBPs in rice: the rice rFKBP64, rFKBP65 and rFKBP75. These FKBPs contain three FKBP12-like domains and a tetratricopeptide repeat (TPR) domain. The expression of the rice FKBPs was found to be regulated by heat stress in various organs. The expression of rFKBP64 at RNA level was elevated by heat stress in roots and shoots and low in mature leaves. The expression of rFKBP65 was detected at the RNA level only after heat stress in all cultivars whereas at the protein level there were differences in the expression between the rice cultivars. The rFKBP75 was expressed at the RNA in all tissues before and after heat stress and the rFKBP75 protein appears to be more abundant after heat stress. The only FKBP to be expressed in seeds was the rFKBP75 which was higher in the embryos and endosperm of dry seeds then in the same organs separated from imbibed seeds, indicating that the protein is important in the steps of seed maturation. In this study we have characterized three large rice FKBPs and have demonstrated that rice FKBPs are heat stress induced and differentially expressed in various tissues indicating specific physiological functions.