White rot fungi produce unique extracellular oxidative enzymes
that degrade lignin and related compounds found in explosive
contaminated materials, pesticides, and toxic wastes. To elucidate
the genetic basis of this technologically important behavior, we
have sequenced the approximately thirty million base-pair genome of
the white rot fungus Phanerochaete chrysosporium to
generate a near chromosome-level assembly using a whole genome
shotgun method. P. chrysosporium was the first
basidiomycete genome to be sequenced, and this improved assembly
provides significantly more contiguity than previously
available.
Lignin plays a key role in the carbon cycle as the most abundant
aromatic compound in nature, providing the protective matrix
surrounding the cellulose microfibrils of plant cell walls. This
amorphous and insoluble polymer lacks stereoregularity and, in
contrast to cellulose and hemicellulose, it is not susceptible to
hydrolytic attack. Although lignin is a formidable substrate, its
degradation by certain fungi was recognized and described over 125
years ago. Collectively referred to as white rot fungi (since
lignin removal often leaves a bleached appearance), these are the
only microbes capable of efficient depolymerization and
mineralization of lignin. All are basidiomycetes, a fungal group
that includes edible mushrooms, mycorrhiza, and plant pathogens
such as smuts and rust.
P. chrysosporium has been the most intensively studied
white rot fungus. White rot fungi secrete an array of peroxidases
and oxidases that act non-specifically via the generation of lignin
free radicals, which then undergo spontaneous cleavage reactions.
The non-specific nature and exceptional oxidation potential of the
enzymes has attracted considerable interest for application in
bioprocesses such as organopollutant degradation and fiber
bleaching.
P. chrysosporium has several features that might make it
very useful in biotechnology applications. First, it efficiently
depolymerizes all the major components of wood. Additionally, it
has a very high optimum temperature (about 40 °C), which means
it can grow on wood chips in compost piles, which attain a very
high temperature.
This is an improved draft assembly of P. chrysosporium,
sequenced using PacBio. The genome assembly used in the previous
annotation, Phchr3_2, has been
re-annotated using a combination of PacBio transcriptomic data
(IsoSeq) as well as new Illumina RNAseq data.
