Extensive sampling of basidiomycete genomes demonstrates inadequacy of the white-rot/brown-rot paradigm for wood decay fungi

TLDR

Wood decay fungi are traditionally classified as white rot, which degrades all cell wall components including lignin, or brown rot, which preserves lignin, and genomic studies show white‑rot species possess multiple lignin‑degrading peroxidases and extensive cellulose‑degrading enzymes. The study aimed to test whether the white/brown‑rot classification adequately describes fungal wood decay by analyzing 33 fungal genomes. The authors examined 33 fungal genomes to assess their lignin‑degrading and cellulose‑degrading enzyme repertoires. Some species lack lignin‑degrading peroxidases yet retain the cellulose‑degrading apparatus typical of white rot and appear to degrade lignin in wood wafer assays, demonstrating that the white‑rot versus brown‑rot paradigm fails to capture the diversity of fungal wood decay mechanisms.

Abstract

Significance Wood decay fungi have historically been characterized as either white rot, which degrade all components of plant cell walls, including lignin, or brown rot, which leave lignin largely intact. Genomic analyses have shown that white-rot species possess multiple lignin-degrading peroxidases (PODs) and expanded suites of enzymes attacking crystalline cellulose. To test the adequacy of the white/brown-rot categories, we analyzed 33 fungal genomes. Some species lack PODs, and thus resemble brown-rot fungi, but possess the cellulose-degrading apparatus typical of white-rot fungi. Moreover, they appear to degrade lignin, based on decay analyses on wood wafers. Our results indicate that the prevailing paradigm of white rot vs. brown rot does not capture the diversity of fungal wood decay mechanisms.