''Magnaporthe rhizophila'' is a fungus species in the family
Magnaporthaceae. These dark mycelial fungi are common
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s of cereal and grass roots.
Rice blast
''Magnaporthe grisea'', also known as rice blast fungus, rice rotten neck, rice seedling blight, blast of rice, oval leaf spot of graminea, pitting disease, ryegrass blast, Johnson spot, neck blast, wheat blast, and Imochi (Japanese:稲熱) is a ...
is one disease known to be caused by M. rhizophila and presents with vascular discoloration in the host organism.
The fungus lives best in drier humid conditions, explaining why it is most often found in the soils of Australia, South Africa, and the Southeastern United States.
Development
Similar to other
ascomycota
Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...
, the lifecycle of ''M. rhizophila'' is split into two parts: the sexual and asexual stages.
The sexual lifestage is characterized by a globose (400-500 um wide)
fruit-like body that contains the sexual spores, called a
perithecia
An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are mos ...
, which occurs in either singles or multiples. Perithecia are flask-like shaped and contain asci, which are septated,
unitunicate
An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or ...
stalks of 8
ascospore
An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or s ...
s. The ascospores are biseriate, fusiform, and slightly curved or helical when naive.
The perithecia is lined with cells called the peridium and has accessory structures called periphyses and paraphyses that surround the outside and inside of the structure, respectively. Paraphyses inside the perithecia dissolve once asci reach maturity. The asexual lifestage is characterized by asexual
conidial structures (6-20x2-6 um).
Conidiophores
A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to ...
are either simple or branched.
Compared to the fruiting bodies of other Magnaporthe species, ''rhizophila'' is considered faster growing (0.8 cm/d at 28 °C)
with slightly longer and wider conidial cells.
''M. rhizophila'' is
homothallic Homothallic refers to the possession, within a single organism, of the resources to reproduce sexually; i.e., having male and female reproductive structures on the same thallus. The opposite sexual functions are performed by different cells of a si ...
, so it is self-fertile and can mate with similar mating types within its own mycelia.
Ecology
''Magnaporthe rhizophila'' is considered a
necrotrophic
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...
parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
because it relies on the nutrients and support of other organisms to thrive. It is a
heterotroph
A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
since it is unequipped to sequester energy on its own, hence its symbiotic behavior. Magnaporthacaea are family-specific soil-borne parasites of
Gramineae
Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and ...
; ''rhizophila'' specifically colonizes the roots of millet.
Spores from ''M. rhizophila'' are dispersed by natural manners such as wind, water, and animals. These spores then settle in soil where they grow and mature through asexual life cycles until it is optimal for the hyphae to resume a sexual cycle and a host organism is near. ''Rhizophila'' is only root-infecting; however many of its Magnaporthe relatives are both soil and aerial-infecting.
The fungus has an
appressorium structure which functions to elicit
effector
Effector may refer to:
*Effector (biology), a molecule that binds to a protein and thereby alters the activity of that protein
* ''Effector'' (album), a music album by the Experimental Techno group Download
* ''EFFector'', a publication of the El ...
hormones to increase host susceptibility (2 clade-specific types of small specific proteins (SSP)
).
Lignitubers have been considered a response by host cells after infection as a response to fungal invasion.
However, ''rhizophila'' kills host cells in 5–6 weeks.
''M. rhizophila'' has darkly pigmented
hypha
A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.
Structure
A hypha consists of one or ...
e, composing
mycelia
Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates ...
that has a gray-brown color, darker than species in the rest of its family.
It is able to be cultured in vitro and survives on PDA (potato dextrose agar) plates.
Geographical distribution
''Magnaporthe rhizophila'' does not necessarily require much water to survive, localizing in drier humid regions of
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
,
South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
, and the
Southeastern United States
The Southeastern United States, also referred to as the American Southeast or simply the Southeast, is a geographical region of the United States. It is located broadly on the eastern portion of the southern United States and the southern por ...
.
Genetics
From data derived from genetic testing, it was found that ''M. rhizophila'' originated in South Africa. Fungal fossils demonstrated that the phyla diverged 31 million years ago from other
Sordariomycetes
Sordariomycetes is a class of fungi in the subdivision Pezizomycotina (Ascomycota), consisting of 28 orders, 90 families, 1344 genera. Sordariomycetes is from the Latin sordes (filth) because some species grow in animal feces, though growth habit ...
, and the
phylogeny
A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...
diverged 21 million years ago from
pezizomycotina
Pezizomycotina make up most of the Ascomycota fungi and include most lichenized fungi too. Pezizomycotina contains the filamentous ascomycetes and is a subdivision of the Ascomycota (fungi that form their spores in a sac-like ''ascus''). It is mo ...
.
Magnaporthe species are grouped into three divergent
clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
s;
rhizophila is in clade classification D along with ''M. poae'' and ''G. incrustans''. ''Rhizophila'' belongs to the Magnaporthe family based on its ascospore morphology; however, it has been considered for the ''
Gaeumannomyces'' because they also produce
phialophora-like
anamorphs
In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota:
*Teleomorph: the sexual reproductive stage (morph), typically a fruiting body.
*Anamorph: an ase ...
instead of
sympodial
Sympodial growth is a bifurcating branching pattern where one branch develops more strongly than the other, resulting in the stronger branches forming the primary shoot and the weaker branches appearing laterally. A sympodium, also referred to a ...
pyricularia.
''M. rhizophila'' is the only known Magnaporthe species with a phialophora anamorph.
Given these similarities between families, ''M. rhizophila'' is highly
hybridized with other species among these groups.
The ''M. rhizophila'' genome is composed of 5.8%
transposable element
A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Transp ...
s, lower than other species in its family.
References
{{Taxonbar, from=Q10575280
Magnaporthales