Genetics of the Unfolded Protein Response in Fungi

Unfolded Protein Response and Scaffold Independent Pheromone MAP Kinase Signaling Control Verticillium dahliae Growth, Development, and Plant Pathogenesis

“…This mutant strain was used for ectopic reintegration of the entire HAC1 gene ( HAC1-C ). Hac1-dependent gene expression levels of the ER chaperone Bip1, a conserved UPR target gene in yeast and filamentous fungi [ 18 ], were determined by quantitative reverse transcription PCR. V. dahliae BIP1 ( VDAG_JR2_Chr3g10940a ) was identified as homolog of the Aspergillus nidulans BipA encoding gene with high amino acid sequence identity of ~76% for the 666 aa protein.…”

“…It mediates expression of genes involved in ER stress relief [ 12 , 13 , 14 , 15 ]. Un- or misfolded proteins in the ER lumen are perceived either by direct interaction with transmembrane receptors such as yeast Ire1 or by interaction of these proteins with the heat shock protein Bip1/Kar2, which dissociates from Ire1 [ 16 , 17 , 18 ]. The cytoplasmic endoribonuclease domain of Ire1 is responsible for unconventional splicing of the mRNA encoding the basic leucine zipper (bZIP) transcription factor Hac1 [ 19 , 20 ].…”

“…Pathogenicity of the smut fungus depends on activation of the UPR after invasion of the plant surface [ 33 , 57 ]. When activated prior to entering the plant cell, the UPR inhibits filamentous growth and virulence by reduction of the pheromone response MAPK pathway activity through dephosphorylation of the MAPK Kpp2, which is mediated by the dual-specificity phosphatase Rok1 [ 18 , 58 ]. In this fungus, rok1 deficient mutant strains displayed increased filamentation and a hyper-virulent phenotype with increased appressorium formation on maize plants.…”