Distinct roles of phytochromes A and B in Aspergillus fumigatus in environmental sensing and pathogenicity

Phytochromes are red-light receptors that regulate gene expression in
response to light and temperature in plants, bacteria, and fungi. In the opportunis
tic pathogenic fungus Aspergillus fumigatus, two putative phytochromes—FphA and
FphB—were characterized to assess any roles in virulence. Spectroscopic analysis of E.
coli-expressed proteins showed that FphA is photoconvertible and functionally similar
to its A. nidulans ortholog, whereas FphB is photoinactive. Therefore, only FphA could
rescue an A. nidulans fphA-deletion mutant. Gene deletion in A. fumigatus revealed that
loss of FphA had no effect on virulence, while deletion of FphB—alone or with FphA—
significantly increased virulence in a Galleria mellonella infection model. Transcriptomic
data linked FphB to the regulation of the neosartoricin B biosynthetic gene cluster
and the production of the prenylated nonribosomal peptide hexadehydroastechrome,
suggesting a role in regulating secondary metabolism. Localization studies showed FphA
at the mitochondria and in nuclei and FphB mainly in the cytoplasm; both proteins form
heterodimers in the cytoplasm and in nuclei. ... mehrThese findings suggest that while FphA acts
as a light and temperature sensor, FphB modulates virulence and may represent a novel
regulatory factor in fungal pathogenicity.