The Ustilaginomycotina is a subdivision within the division

Basidiomycota Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basi ...

of the kingdom

Fungi 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 ...

. It consists of the classes Ustilaginomycetes and Exobasidiomycetes, and in 2014 the subdivision was reclassified and the two additional classes

Malasseziomycetes ''Malassezia'' (formerly known as ''Pityrosporum'') is a genus of fungi. It is the sole genus in family Malasseziaceae, which is the only family in order Malasseziales, itself the single member of class Malasseziomycetes. ''Malassezia'' species ...

and Moniliellomycetes added. The name was first published by Doweld in 2001; Bauer and colleagues later published it in 2006 as an

isonym An isonym, in botanical taxonomy, is a name of a taxon that is identical to another designation, and based on the same type, but published at a different time by different authors. Citation from that source follows: That is, the later isonyms ...

. Ustilagomycotina and

Agaricomycotina The subdivision Agaricomycotina, also known as the hymenomycetes, is one of three taxa of the fungal division Basidiomycota (fungi bearing spores on basidia). The Agaricomycotina contain some 20,000 species, and about 98% of these are in the clas ...

are considered to be sister groups, and they are in turn sister groups to the subdivision

Pucciniomycotina Pucciniomycotina is a subdivision of fungus within the division Basidiomycota. The subdivision contains 9 classes, 20 orders, and 37 families. Over 8400 species of Pucciniomycotina have been described - more than 8% of all described fungi. The s ...

. Ustilaginomycotina comprises 115 genera with more than 1700 species. The subdivision is mostly plant parasites on vascular plants, and the distribution of the subdivision is therefore restricted to the distribution of the host. The group is also called the true smut fungi because of the production of

teliospores Teliospore (sometimes called teleutospore) is the thick-walled resting spore of some fungi ( rusts and smuts), from which the basidium arises. Development They develop in '' telia'' (sing. ''telium'' or ''teliosorus''). The telial host is the p ...

. The name smut is still used as a term since it circumscribes the organization and life cycle of Ustilaginomycotina, but it is not a

taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

term. Ustilaginomycotina has some of the best known and studied genera of plant parasites like ''

Ustilago ''Ustilago'' is a genus of approximately 200 smut fungi parasitic on grasses. Uses ''Ustilago maydis'' is eaten as a traditional Mexican food in many parts of the country, and is even available canned. Farmers have even been known to spread th ...

'' and ''

Tilletia ''Tilletia'' is a genus of smut fungi in the Tilletiaceae family. Species in this genus are plant pathogens that affect various grasses. '' Tilletia indica'', which causes Karnal bunt of wheat, and '' Tilletia horrida'', responsible for rice ker ...

'' and it is also of great economic importance.

Morphology

Ustilaginomycotina is morphologically a highly diverse group. It consists of two states: anamorphic

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...

state and teleomorphic filamentous smut state. These two states in the life cycle can look very different.

Defining features

The Ustilaginomycotina has different ultrastructural morphologies that defines the subdivision and some of them are also used to delimit the classes in the subdivision. Cellular interaction The cellular interactions are referring to the interaction between the

hyphae 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 ...

and the host plant cells. These zones provide a useful ultrastructural character for delimiting the classes in Ustilaginomycotina. The host-interactions zones can either be local interaction zones and then characterizing the Exobasidiomycetes, or enlarged interaction zones characterizing the Ustilaginomycetes. Cellular composition Ustilaginomycotina has a distinctive cell wall composition consistent of mostly

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

and absence of

xylose Xylose ( grc, ξύλον, , "wood") is a sugar first isolated from wood, and named for it. Xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes an aldehyde functional gro ...

. This character separates the Ustilaginomycotina from Pucciniomycotina and Agaricomycotina. Septal pores The architecture of the septal pores plays an important part in delimiting the subdivision in Basidiomycotina. In contrast to the Pucciniomycotina, the Ustilaginomycotina has a septal pore with a membrane cap or it is poreless. It does not have a

dolipore Dolipore septa are specialized dividing walls between cells (septa) found in almost all species of fungi in the phylum Basidiomycota. Unlike most fungal septa, they have a barrel-shaped swelling around their central pore, which is about 0.1–0. ...

parenthesome Within the cells of some members of basidiomycetes fungi are found microscopic structures called parenthesomes or septal pore caps. They are shaped like parentheses and found on either side of pores in the dolipore septum which separates cells wit ...

as the Agaricomycotina do. 5S rRNA In 1985 Gottschalk and Blanz did a study about the 5s ribosomal

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

and distinguished two types of structures in the Basidiomycota. These two types was named the type A secondary structure and the type B secondary structure of the 5S rRNA. This is a useful tool for delimiting between the subdivisions. The Ustilaginomycetina has the type B secondary structure and they share this character with the Agaricomycotina, and it separates them from the Pucciniomycotina which has the type A secondary structure.

Classification

Historic classification

In 1847 Tulasne and Tulasne divided the so-called smut fungi into two groups called Ustilaginacceae and Tilletiaceae. Traditionally morphological characters of the basidia was used for the delimitation of the smut fungi group, but after a thorough investigation of the

ultrastructural Ultrastructure (or ultra-structure) is the architecture of cells and biomaterials that is visible at higher magnifications than found on a standard optical light microscope. This traditionally meant the resolution and magnification range of a co ...

characters the group was revised. With the use of

electron microscopy An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...

, Bauer et al. 1997 found two separates lines of the smut fungi, namely the

Microbotryales The Microbotryales are an order of fungi in the Microbotryomycetes class of the Basidiomycota. The order contains 2 families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity ...

(which is now moved to Puzziniomycotina) and the Ustilaginomycetes. Within the Ustilaginomycetes they identified three lineages: the Entorrhizomycetidea, Ustilaginomycetidae and the Exobasidiomycetidae.

Modern classification

Ustilaginomycotina consists of both anamorphic

species and teleomorphic filamentous smuts. These two states can look very different and is not always easy to connect. The two different states has therefore produced different names on the same species. With the use of both morphological characters and molecular data, the subdivision is now reclassified and many of the species has been renamed by the 'One Fungus = One Name' principle.' By looking at ultrastructural morphological structures like host-parasite interactions, the septal pore apparatus and molecular sequence analysis a new classification was proposed. Here Ustilaginomycotina consisted of the three classes Ustilaginomycetes, Exobasidiomycetes and Entorrhizomycetes. But, the presence of Entorrhizomycetes was questioned and are now considered as incertae sedis in the

. In 2014 a new multiple gene sequence analysis showed that two additional classes, forming two independent deep lineages should be recognized as classes in the subdivision:

and Moniliellomycetes.

Ecology

Distribution

Since Ustilaginomycotina is mostly plant parasites, the group is restricted to the host species of

vascular plants Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They al ...

, and mainly on

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

and monocots. This encompasses a geographical distribution in both tropical, temperate and arctic regions. Most species are highly host-specific and this may be a product of

coevolution In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well ...

with different angiosperm lineages. This is supported by studies that shows that some

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

lineages in the Ustilaginomycotina are restricted to monophyletic lineages in the angiosperms. But not all taxa in Ustilaginomycotina are host-specific, some have a broad host range and others have also made a host jump to other vascular plants and not only monocots in the angiosperms.

Role in the environment

Ustilaginomycotina have an array of plant pathogens, and some are parasitizing on economically important species like wheat, barley and corn. In some cases the yield loss is minimal, in other the crops has to be quarantined. Some of the galls produced by the smuts is considered as a delicacy in some parts of the world. ''Malassezia'' lineages also causes harm on human skin. ''

Ustilago maydis Corn smut is a plant disease caused by the pathogenic fungus ''Ustilago maydis'' that causes smut on maize and teosinte. The fungus forms galls on all above-ground parts of corn species. It is edible, and is known in Mexico as the delicacy ''h ...

'' ''

Malassezia ''Malassezia'' (formerly known as ''Pityrosporum'') is a genus of fungi. It is the sole genus in family Malasseziaceae, which is the only family in order Malasseziales, itself the single member of class Malasseziomycetes. ''Malassezia'' species ...

Life cycle

The life cycle of the subdivision is dimorphic and it consists of two phases in the life cycle. One saprobic

haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

phase and a parasitic ( biotrophic)

dikaryotic The dikaryon is a cell nucleus, nuclear feature which is unique to certain fungi. (The green alga ''Derbesia'' had been long considered an exception, until the heterokaryotic hypothesis was challenged by later studies.) Compatible cell-types can fus ...

phase. The saprobic phase is initiated by the production of haploid yeasts, which fuses with another spore and produce the n+n hyphae which will infect the host. The infection happens with the production of a structure called an

appressorium An appressorium is a specialized cell typical of many fungal plant pathogens that is used to infect host plants. It is a flattened, hyphal "pressing" organ, from which a minute infection peg grows and enters the host, using turgor pressure capable ...

, which is generated by a specialized cell used to penetrate the host

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

. Inside the host, the fungi will produce hyphae and another specialized structure called haustoria. This will take nutrition from the plant, and is a parasitic feature. Almost all of the Ustilaginomycotina will then sporulate inside the host, and this happens with the spore becoming thick-walled and will separate, now called a teliospore. The teliospore is the most conspicuous part of the individual and represent the smut syndrome. This teliospore is a specialized resting spore that can survive outside their host. The teliospore is released from the host, and it will produce a diploid basidium and the cycle starts over. Species from the subdivision obtained from the nature will often be in the yeast-like state.

References

External links

Tree of Life Ustilaginomycotina
{{Taxonbar, from=Q1204312 Taxa described in 2001