Abstract
The multiprotein-bridging factor 1 (MBF1) gene family is well known in archaea, non-lichenized fungi, plants, and animals, and contains stress tolerance-related genes. Here, we identified four unique mbf1 genes in the lichenized fungi Endocarpon spp. A phylogenetic analysis based on protein sequences showed the translated MBF1 proteins of the newly isolated mbf1 genes formed a monophyletic clade different from other lichen-forming fungi and Ascomycota groups in general, which may reflect the evolution of the biological functions of MBF1s. In contrast to the lack of function reported in yeast, we determined that lysine114 in the deduced Endocarpon pusillum MBF1 protein (EpMBF1) had a specific function that was triggered by environmental stress. Further, the Endocarpon-specific C-terminus of EpMBF1 was found to participate in stress tolerance. Epmbf1 was induced by a number of abiotic stresses in E. pusillum and transgenic yeast, and its stress-resistant ability was stronger than that of the yeast mbf1. These findings highlight the evolution and function of EpMBF1 and provide new insights into the co-evolution hypothesis of MBF1 and TATA-box-binding proteins.
Highlights
Multiprotein-bridging factor 1 (MBF1) is a transcriptional co-activator
We identified additional homologs of multiprotein-bridging factor 1 (MBF1) in lichens and we investigated whether changes in the amino acid sequence of MBF1 unique to the desert lichen Endocarpon pusillum Hedw. affect stress tolerance, which is an important hypothesized function of these proteins[13,17]
A BLASTP analysis of the deduced amino acid sequence revealed that Endocarpon pusillum MBF1 protein (EpMBF1) shared 46% and 41% identities with the MBF1 sequences of Fusarium verticillioides (GenBank: EWG40545.1) and S. cerevisiae (GenBank: BAA33217.1), respectively
Summary
Multiprotein-bridging factor 1 (MBF1) is a transcriptional co-activator. MBF1 acts as a linker between TATA-box-binding proteins (TBPs) and sequence-specific transcription factors to activate transcription of downstream genes[1]. The HTH domain is responsible for the functional activity of MBF1, and differences in the N- and C-termini do not affect the main activities of MBF1 proteins[3,4]. A compensatory change analysis found that the yMBF1D112K mutant [D112 changed to lysine (K)112] did not interact with yTBP in yeast[5] This site (D112 in yMBF1) is conserved in this position in most fungal MBF1s6, while the D is replaced by glutamic acid (E) in plant and animal MBF1s. Mbf1s from Arabidopsis, invertebrates, and vertebrates were capable of complementing the yeast Δmbf[1] mutant[14,15] These findings suggested that the MBF1 domain for binding basic transcription factors www.nature.com/scientificreports/. It is intriguing to understand the functions of the mbf[1] gene of E. pusillum and determine if the MBF1 protein family undergoes environmental selection during the evolutionary process
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