Centrin association with the flagellar apparatus in spores of Phytophthora cinnamomi

Antibodies raised against the calcium-binding protein centrin, were used to identify and localise centrin containing structures in the flagellar apparatus of zoospores and cysts of the oomycete Phytophthora cinnamomi. Immunoblotting of extracts from zoospores indicates that the P. cinnamomi centrin homologue is a 20 kDa protein. Immunofluorescence microscopy with anti-centrin antibodies reveals labelling in the flagella, the basal body connector and co-localisation along the microtubular R1 root (formerly called AR3) that runs from the right side of the basal body of the anterior flagellum into the anterior of the zoospore close to the ventral surface. The centrin (R1^cen) and tubulin components of the R1 root split into four loops on the right hand side of the ventral groove and rejoin along the left hand side of the groove. The R1 root continues down the left hand side of the zoospore past the basal bodies and parallel to the R4 root. We propose that at least in P. cinnamomi there is no R2 root. Immunogold labelling confirms that centrin is a component of the basal body connector complex. When the zoospores become spherical during encystment, the R1^cen pivots by approximately 90 ° with respect to the nucleus.