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Localization and activity of the calcineurin catalytic and regulatory subunit complex at the septum is essential for hyphal elongation and proper septation in Aspergillus fumigatus
Author(s) -
Juvvadi Praveen Rao,
Fortwendel Jarrod R.,
Rogg Luise E.,
Burns Kimberlie A.,
Randell Scott H.,
Steinbach William J.
Publication year - 2011
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2011.07886.x
Subject(s) - biology , calcineurin , aspergillus fumigatus , protein subunit , microbiology and biotechnology , nuclear transport , nuclear export signal , biochemistry , gene , cell nucleus , cytoplasm , medicine , transplantation
Summary Calcineurin, a heterodimer composed of the catalytic (CnaA) and regulatory (CnaB) subunits, plays key roles in growth, virulence and stress responses of fungi. To investigate the contribution of CnaA and CnaB to hyphal growth and septation, Δ cnaB and Δ cnaA Δ cnaB strains of Aspergillus fumigatus were constructed. CnaA colocalizes to the contractile actin ring early during septation and remains at the centre of the mature septum. While CnaB's septal localization is CnaA‐dependent, CnaA's septal localization is CnaB‐independent, but CnaB is required for CnaA's function at the septum. Catalytic null mutations in CnaA caused stunted growth despite septal localization of the calcineurin complex, indicating the requirement of calcineurin activity at the septum. Compared to the Δ cnaA and Δ cnaB strains, the Δ cnaA Δ cnaB strain displayed more defective growth and aberrant septation. While three Ca 2+ ‐binding motifs in CnaB were sufficient for its association with CnaA at the septum, the amino‐terminal arginine‐rich domains (16‐RRRR‐19 and 44‐RLRKR‐48) are dispensable for septal localization, yet required for complete functionality. Mutation of the 51‐KLDK‐54 motif in CnaB causes its mislocalization from the septum to the nucleus, suggesting it is a nuclear export signal sequence. These findings confirm a cooperative role for the calcineurin complex in regulating hyphal growth and septation.