Proteins localized to peroxisomes, particularly those expressed under specific conditions
or in low abundance, are often undetected by routine proteomics methods due to detection
sensitivity limits. In silico identification and experimental validation of peroxisomal
targeting signals (PTSs) offer a reliable alternative. We demonstrate that SYM, a
non-canonical plant PTS-1 signal, functions similarly in Aspergillus nidulans , as
GFP tagged with a SYM C-terminal tripeptide localizes to peroxisomes. One of two native
A. nidulans proteins with C-terminal SYM tripeptide shows weak peroxisomal localization
alongside cytoplasmic presence, indicating that only a subset of proteins with non-canonical
signals access peroxisomes. In silico analysis of 1,010 fungal genomes identified
diverse SYM-proteins with variable functions, suggesting that non-canonical PTS-1
signals may evolve spontaneously. Two-thirds of SYM-proteins are predicted to localize
to specific intracellular compartments other than the peroxisome. We propose that
despite their predicted localization, these proteins possessing SYM as a non-canonical
peroxisomal signal might also have peroxisomal presence. Among SYM-proteins, pectinesterases,
known plant pathogen virulence factors, were frequent. Notably, 25% of fungal pectinesterases
harbor non-canonical PTS-1 signals, suggesting that partial peroxisomal localization
of pectinesterases has evolved convergently. This suggests that partial peroxisomal
localization may enhance protein functional flexibility, contributing to the organism’s
adaptability.
