Melampsora allii-populina is a rust fungus (Pucciniales) that belongs to the Melampsoraceae family and is closely related to Melampsora larici-populina, the first poplar rust fungus sequenced by the Joint Genome Institute. Both rust fungi can cause damage in poplar plantations. Rust fungi are obligate biotrophs and have the most complex life cycle known in fungi with one or two alternate host species and up to five distinct spore forms (sexual and asexual). Both poplar rust fungi sequenced by JGI are heteroecious and share poplar as a telial host, on which they produce large amounts of asexual spores (urediniospores) responsible for epidemics. Interestingly, they possess different aecial hosts on which they perform sexual reproduction, i.e. Allium spp., Arum spp. and Muscari spp. (all of which are monocots) for M. allii-populina and Larix spp. (conifers) for M. larici-populina.
The genome of M. allii-populina was sequenced in the
frame of the JGI
1000 Fungal Genomes Project to explore the molecular bases of
host adaptation by identifying the common sets of genes that are
necessary to infect poplar and those that differ and may be
specific to infection of Allium and Larix.
Rust fungi are notorious for their large genome size compared to
other basidiomycetes. M. allii-populina represents
one of the largest fungal genomes sequenced to date, at ~336Mb.
Additionally, this genome is quite a bit larger than the two
relatives already sequenced in the Melampsoraceae family (i.e. ~110
Mb for M. larici-populina and ~190
Mb for the flax rust M. lini).
Some of this difference may be due to the sequencing platform, as
M. allii-populina is the first member of this family
sequenced with PacBio.
