Role of High Mobility Group B protein HmbA, orthologue of yeast Nhp6p, in Aspergillus nidulans

The mammalian HMGB1 protein belongs to the high-mobility-group B (HMG-B) family, which is not only architectural but also functional element of the chromatin. The fungal counterpart of HMGB1 was identified in Saccharomyces cerevisiae as Nhp6p and the pleiotropic physiological functions of this protein were thoroughly studied during the last decades. Although filamentous Ascomycete fungi also possess the orthologues of Nhp6p, their physiological functions, apart from their role in the sexual development, have not been investigated, yet. Here we study the physiological functions of the Nhp6p orthologue HmbA from Aspergillus nidulans in the primary and secondary metabolism, stress tolerance, hypha elongation and maintenance of polarized growth through the analysis of hmbA deletion mutant. We also revealed that the endochitinase ChiA acts in the cell wall remodelling and contributes to polar growth. Additionally, by conducting heterologous expression studies, we further demonstrated that HmbA and Nhp6p is interchangeable for several functions. We hypothesized that the fully complemented functions might predominantly depend on the DNA binding ability of the HmbA and Nhp6p proteins rather than on the interaction of these HMG-B proteins with other functional protein components of the chromatin.