Mucor rouxii Rho protein characterization and its posible role in polarized growth

SILVIA ARGIMON; FIORELLA GALELLO; ELBA PEREYRA; SILVIA ROSSI; SILVIA MORENO

ANTON LEEUW INT. J. G.

SPRINGER

Año: 2007 vol. 91 p. 237 - 251

0003-6072

We have already shown that protein kinase A of the medically important zygomycete Mucor rouxii participates in fungal morphology through cytoskeletal organization. As a first step towards finding the link between protein kinase A and cytoskeletal organization we here show the cloning of the Rho1 gene and the characterization of its protein product. The Rho1 protein primary sequence shows 70-85 % identity with fungal Rho1 or mammalian RhoA. Two protein kinase A phosphorylation sequences in adequate context are predicted. The over-expressed Rho1 fully complements a Saccharomyces cerevisiae null mutant. The endogenous protein is identified by western blot against a developed antibody and by ADP-ribosylation. Localization in germlings is visualized by immunofluorescence; the protein shows to be localized in patches in the mother cell surface and excluded from the germ tube. Measurement of Rho1 expression during germination indicates that Rho1, at both mRNA and protein levels, correlates with differentiation and not with growth. Rho1 has been shown to be the regulatory protein of the b-1,3-glucan synthase complex in fungi in which b-1,3-glucans are major components of the cell wall. Even though glucans have not been detected in zygomycetes, caspofungin, an echinochandin known to be an inhibitor of b-1,3-glucan synthase complex, is shown here to have a negative effect on growth and to produce an alteration on morphology when added to Mucor rouxii growth culture medium. This result has an important impact on the possible participation of b-1,3-glucans on the regulation of morphology of zygomycetes.