COURSE TEACHERDR. A.S. KRISHNAMOORTHY

STUDENTMOHAMMED FAISAL P

INTRODUCTION

Ascomycota are fungi which possess an ascus, containing ascospores, formed after karyogamy and meiosis.

The ascomycota is the largest phylum of fungi having almost 45 % of the desribed species.

Now, with the merger of the Deuteromycetes another 20% of the described species have been assed to this group.

(Taylor, 1995)

Domain – Eukarya

Kingdom – Fungi

Development of asci

Archiascomycetes includes 11 orders of which four orders are very important

Family Taphrinaceae

Genus Taphrina

Species T. deformans, T. maculans

Taphrina deformans hyphae growing in intercellular spaces secrete polysaccharide-degrading enzymes, such as cellulase, causing partial dissolution of the host cell wall.

This process also results in changes in the plasma membrane.

T. deformans also produces the auxin indole-3-acetic acid from L-tryptophan via indole-3-pyruvic acid and indole-3-acetaldehyde.

This process is thought to be responsible for the hyperplastic effect of the infection.

Ascomyces deformans Berk., (1860)Exoascus amygdali Jacz., (1926)Exoascus deformans (Berk.) Fuckel, (1870)Taphrina amygdali (Jacz.) Mix, (1936) 

Disease cycle of peach leaf curl and plum pocket caused by Taphrina sp.

• In liquid cultures, especially on media containing tryptophane, considerable quantities of the auxin-type phytohormone indole acetic acid (IAA) have been demonstrated.

• A number of different cytokinins are also produced by several species of Taphrina in culture

(Kern & Naef-Roth, 1975; Tudzynski, 1997)

The classification of the Schizosaccharomycetales has been the subject of controversial discussions, but the emerging consensus is that there is only one genus with three species, S. japonicus, S. octosporus and S. pombe.

(Barnett et al., 2000).

Grow as saprotrophic yeasts which reproduce asexually by fission, i.e. by division of a vegetative cell into two daughter cells of equal size.

Schizosaccharomyces is therefore called the fission yeast

Schizosaccharomyces octosporus.(a) Vegetative cells, showing transverse division, conjugating

(b) Four- and eight-spored asci.

The life cycle of the homothallic yeast Schizosaccharomyces octosporus.

The cytoskeleton and the cell cycle in Schizosaccharomyces pombe

Consist of 8 familes and 75 genera

Characterized by direct development of asci from the zygote, lack mycelium and absence of ascomata

Pseudomycelium – hyphae consisting of cells formed by budding

8 families are

• About 10-16 species of Saccharomyces are currently recognized

(Barnett et al., 2000; Kirk et al., 2001)

• S. cerevisiae, which in many ways is the most important fungus yet discovered.

• About 25 strains of S. cerevisiae exist, and these have different physiological properties which are relevant to their biotechnological applications

Saccharomycetaceae

Sketch of a budding yeast cell

Life cycle of S. cerevisiae

The structure of the mating type idiomorphs a (top) and α (bottom) of Saccharomyces cerevisiae

The two alleles differ only in their central (Y) regions which contain parts of two genes a1and a2 or a1and a2.The function of a2 is unknown.In diploid cells,the lack of expression of a1 and the formation of a dimeric α2/a1 protein suppresses the expression of mating type-specific proteins including hormones and their receptors

(Annual Reviews of Genetics, 32, 1989)

• Alcoholic fermentation mainly by Saccharomyces cerevisiae. This is the oldest and yet still the most important area of biotechnology, with about 1011 l of beer and 3X1010 l ofwine produced worldwide each year

(Oliver, 1991; Kurtzman & Sugiyama, 2001)

• Bread-making. About 1.5 X 106 tons of fresh cells of S. cerevisiae are produced worldwide per annum for use in the production of bread dough

Applications of Saccharomyces

• Single-cell protein (SCP). This term describes the conversion of low-cost substrates into protein- rich biomass of unicellular organisms.

• Vitamin production. Riboflavin (vitamin B2) is produced industrially.

• Production of recombinant proteins, e.g. enzymes, or clinically relevant molecules such as antigens, insulin and epidermal growth factor.

Expression systems for heterologous proteins, i.e. proteins of interest whose gene has been linked to the promoter sequence of the producing organism.

• Single family

• Protomycetaceae comprising of five genera

• Attack flowering plant and cause lesions and galls

• Special characeter is formation of vesicle - synascus

Life cycle of Protomyces macrosporus

Compiled from Alexopoulos et al (1996), Sugiyama (1998) and Landvik et al (2003)

Filamentous ascomycetes (informally called euascomycetes) are the most evolved members of phylum Ascomycota

Traditionally segregated based on morphology of ascomata

rDNA sequences has shown the division into classes to be untenable

Study of these class are made know in order of alphabetical sequence as their evolutionary relationships are not clear.

(Berbee and Taylor, 1999)

Orders and families

Largest order of phyllum Ascomycota, 58 familes and 711 genera and 4774 species.

Ascospores are septate

two important families

•Mycosphaerella is one of the largest genera of ascomycetes, containing over 2000 described species

(Corlett, 1991)

• Several related Ascochyta-type anamorphs infect legumes, causing diseases such as blight of chickpea (A. rabiei), foot rot and blight of peas (A. pinodes), and leaf and pod spot of broad beans (A. fabae) and peas (A. pisi).

• The pseudothecial state, where present, is now called Didymella (formerly Mycosphaerella).

Conidia and Ascomata

Symptoms of Mycosphaeralla

Family - Venturiaceae

The mycelium in living tissues is located only between the cuticle and the epidermal cells.

There, it produces short, erect, brownish conidiophores that give rise to several, one- or two-celled, Spilocaea-type conidia of rather characteristic shape

Genus Venturia

Species V. inaequalis

Life cycle of Venturia inaequalis

• 13 families and 2000 species

• One important family

• Members of families produce stalked apothecia which grow from stromata located within the colonized host plant tissue.

• In Sclerotinia the apothecia arise from a seed like sclerotium which, though formed in host tissue, fall off to lie in the soil.

• The conidial stage is represented by Botrytis.

• Monilinia forms apothecia on mummified and stromatized fruits; the conidial stage is Monilia

Family - Sclerotiniaceae

GENUS - Sclerotinia Sclerotia of

the fungus

inside a

tomato stem

Sclerotia of

the fungus

inside a

tomato stemStem rot or

white mould

in pepper

Stem rot or

white mould

in pepper

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Disease cycle of Sclerotinia

• The mycelium produces chains of elliptical Monilia- type conidia on hyphal branches arranged in tufts (sporodochia).

• The fungus also produces microconidia (spermatia) in chains on bottle-shaped condiophores.

• The sexual stage, the apothecium, originates from pseudosclerotia formed in mummified fruit buried partly or wholly in the soil or debris.

Monilinia fructicola

Symptoms caused by Monilinia on peach

The life cycle of Monilinia fructicola

Black Mildew Black mildew is widespread in bamboo stands, especially in humid tropical areas with closed canopy

Cobweb-like to powdery black patches appear on the upper surfaces of mature leaves.

As the infection develops, the upper leaf surface becomes densely coated with a black powdery growth of fungal hyphae

Meliola fabri parasitic on Castanopsis fabri and Meliola hosagoudarii parasitic on Tutcheria microcarpa

• Ceratocystis fimbriata, causing canker diseases on cacao, coffee, stone fruits

• Includes opperculate discomycetes.

• 17 families and 177 genera

• Families are Ascobolaceae, Helvellaceae, Morchella, Otideaceae, Pezizaceae amd Tuberaceae

• Ascobolus is the type genus, having 50 species most of which forms apothecia on dung of herbivore animals

MORPHOLOGY OF Ascobolus sps

Ascobolus immersusAscobolus furfuraceus

• Single family – Phyllachoraceae and 42 genera

• The anamorphs are coelomycetous mitosporic fungi.

• 2 important genera

Order - Phyllachorales

PhyllachoraPhyllachora

GlomerellaGlomerella

• G. cingulata causing many anthracnose diseases and bitter rot of apples; anthracnose of mango, banana its anamorphic stage is Colletotrichum gloeosporioides

Genus – Glomerella

• Forms perithecia or clestothecia

• Asci are cylinderical or clavate

• Conidia stage is absent or sometimes spermatial

• Most are saprobes

• 8 families two are important– Cheatomiaceae– Sordariaceae

• Beaked or ostiolate perithecia with ornamental hairs

• Asci are spherical or globose

• Anamorphs are absent

• Genus – Cheatomium – cellulose degarding fungi

• 80 species are recorded.

Family - Cheatomiaceae

• Most species of Sordaria are cellulolytic.

• Perithecia are common on the dung of herbivores and occasionally on other substrata such as seeds and plant remains, while a few species are reported from soil.

• Sordaria fimicola is especially common on horse dung and has been widely used in experiments on nutrition, the physiology of fruiting, spore liberation and genetics.

FAMILY - SORDARIACEAE

a) L.S. Perithecium. (b) Ascus apex. (c) Ascospore showing mucilaginous epispore.

• There are about 12 species of Neurospora, mostly growing on soil.

• Neurospora has been widely used in genetic and biochemical studies

• The development of auxotrophic mutants deficient in successive steps of arginine biosynthesis led to the proposition of the ‘one- gene-one-enzyme’ hypothesis by Beadle and Tatum (1941) who were awarded the Nobel Prize in 1958.

• The loci of over 1000 genes have been mapped (Perkins et al., 2000)

• complete genome of N. crassa has now been sequenced. It is haploid and has seven chromosomes.

Genus - Neurospora

Life cycle and mating types in Neurospora

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