Escobar / Fenoll Plant Nematode Interactions

A View on Compatible Interrelationships
1. Auflage 2015
ISBN: 978-0-12-417180-0
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, Band Volume 73, 440 Seiten

Reihe: Advances in Botanical Research

Advances in Botanical Research publishes in-depth and up-to-date reviews on a wide range of topics in plant sciences. Currently in its 73rd volume, the series features several reviews by recognized experts on all aspects of plant genetics, biochemistry, cell biology, molecular biology, physiology and ecology. This thematic volume features reviews on molecular and developmental aspects of the compatible plant-nematode interaction.ÿ The contributors all actively work in the field of molecular genetics and genomics of plant parasitic nematodes and nematode feeding sites.ÿ Reviews focus on molecular and physiological aspects of nematode feeding site development and includes specific chapters on nematode effectors as well as plant responses. - Publishes in-depth and up-to-date reviews on a wide range of topics in plant sciences - This volume features reviews of the fast moving field of compatible interaction between plants and sedentary endo-parasitic nematodes - A strong focus on molecular and physiological aspects of nematode feeding site development and includes specific chapters on nematode effectors as well as plant responses

Autoren/Hrsg.

Escobar, Carolina

Fenoll, Carmen

Leseproben

Chapter Two Introductory Chapter on the Basic Biology of Cyst Nematodes
Holger Bohlmann     Department of Crop Sciences, Division of Plant Protection, University of Natural Resources and Life Sciences, Tulln, Austria
E-mail: [e-mail] Abstract
Cyst nematodes are a group of sedentary, biotrophic plant pathogenic nematodes. Their life cycle starts with the hatching of juveniles, often induced by metabolites exuded from the roots of their host plants. They invade the roots with the help of the stylet and cell wall degrading enzymes produced in the subventral gland cells and move intracellularly to the central cylinder where they induce a feeding site with effectors produced mainly in the dorsal gland cell. Starting from the initial syncytial cell, several hundred root cells are incorporated into a syncytium by local cell wall dissolutions. This syncytium is the only source of nutrients for the cyst nematodes which they take up through their stylet and a feeding tube produced in the syncytium at the tip of the stylet. Males become mobile again after the fourth moult and leave the roots to mate with females. The females stay attached to their feeding site during their whole life and produce hundreds of eggs after mating. The majority of eggs will be contained in the female body. When the female dies, its body will harden and become the cyst which protects the eggs. Cysts can survive in the soil for many years until the new generation of juveniles will hatch again under favourable conditions. Keywords
Globodera; Hatching; Heterodera; Stylet; Syncytium 1. Introduction
Nematodes are widely distributed on earth and occur in almost all ecosystems. They can be free living, feeding on bacteria (such as the model organism Caenorhabditis elegans) or fungi or live as parasites of animals and plants. Animal parasites include, for instance, entomopathogenic nematodes which are used in plant protection against insect pests (Dillman & Sternberg, 2012). They can also cause important diseases of animals and humans. Ascaris lumbricoides may be found in more than 1 billion people (Dold & Holland, 2011). The guinea worm (Dracunculus medinensis), whose females can become as long as 80 cm, was traditionally removed by pulling it out from the wound and wind it up on a wooden stick (Muller, 1971). Some think that this is what is shown on the Rod of Asclepius, the medical symbol. Decraemer and Hunt (2006) have reported that 4100 species are regarded as plant parasitic nematodes which occur mainly on the roots of their host plants. Since plant parasitic nematodes live usually belowground and may not always induce obvious symptoms on the aboveground plant parts, it is clear that many more species are still to be discovered. According to their life style they can be divided into migratory and sedentary parasites. Molecular phylogenetic studies have revealed that the parasitic life style in these groups has evolved independently several times (Holterman et al., 2009). Cyst nematodes and root knot nematodes are the main groups of the sedentary parasites. Nematodes belong to the phylum nematoda with the cyst nematodes in the order Tylenchida. Cyst nematodes are found in the subfamily Heterodeninae which was formerly placed in the family Heteroderidae (Evans & Rowe, 1998) with 6 genera and a total of 99 species. The largest genus Heterodera had 67 species and Globodera 12. Now, with increasing use of molecular markers in systematics, the cyst nematodes (subfamily Heterodeninae) have been placed in the family Hoplolaimidae with currently 8 genera with 115 species in the subfamily Heterodeninae: Heterodera, Globodera, Cactodera, Punctodera, Dolichodera, Betulodera, Paradolichodera and Vittatidera (Turner & Subbotin, 2013). The number of cyst nematode species will certainly increase in the future. The far largest genus is still Heterodera with now 82 species, which, together with the genus Globodera (12 species) contains many species of global agronomic importance. Accordingly, most of what we know about cyst nematodes comes from research on Heterodera schachtii, the sugar beet cyst nematode, and Heterodera glycines, the soybean cyst nematode and from the potato cyst nematodes, Globodera rostochiensis (called the “golden nematode” because the females have a yellow or golden colour) and Globodera pallida (called the “pale potato cyst nematode” because the females are cream coloured). Other cyst nematodes on important crop plants (reviewed by Nicol et al., 2011) include Heterodera oryzicola, Heterodera elachista, Heterodera oryzae and Heterodera sacchari on rice and Heterodera zeae, Heterodera avenae and Punctodera chalcoensis on maize. Cereal cyst nematodes are a global problem in wheat-producing countries. The cereal cyst nematode complex includes several closely related species, especially H. avenae, but also Heterodera filipjevi and Heterodera latipons (Nicol, Elekcioglu, Bolat, & Rivoal, 2007). 2. Morphology
A detailed description of cyst nematode morphology and ultrastructure is given by Zunke and Eisenback (1998). In brief, juvenile cyst nematodes (Figure 1) are vermiform and measure between 330 and 700 µm while the males are approximately twice as large, between 450 and 1700 µm. Mature Globodera females are nearly round while females of Heterodera species have a lemon-shaped body. They vary in length from 300 to 990 µm and in width from 200 to 810 µm. Juveniles have a dome-shaped head region and a tapering tale. The body is covered with an elastic cuticle which is secreted by the hypodermis and may be coated with proteins, carbohydrates and lipids which could be important in the suppression or evasion of host defences (Curtis, 2007). Robertson et al. (2000) cloned a gene from Globodera rostochiensis which encoded a peroxidase. The protein, although lacking a signal peptide, was detected on the surface of juveniles and might be involved in protection against plant defence responses such as the production of reactive oxygen induced through the damage caused by the migrating juvenile. During infection of Arabidopsis roots by H. glycines juveniles the root cells produced hydrogen peroxide which could be detected histochemically (Waetzig, Sobczak, & Grundler, 1999). During moulting, the old cuticle is removed and a new cuticle is formed. Nematodes lack a skeleton and the cuticle is therefore important to maintain the shape, together with the hydroskeleton formed by the inner pseudocoelom which is lined by longitudinal muscle cells. Movement is accomplished by alternating contraction of the ventral and dorsal muscle cells. Other specialized muscle cells exist at the mouth to move the stylet, at the oesophagus, and along the digestive tract and the reproductive system.
Figure 1 Longitudinal view (LV) through the anterior region. Insert: LV showing a closed valve or end apparatus within a dorsal gland ampulla and the open valve or end apparatus within one of a pair of subventral gland ampullae (Endo, 1984). Copyright 1984 by the Helminthological Society of Washington, used with permission. Nematodes have a simple central nervous system with a major anterior, circumpharyngeal nerve ring in the head region and dorsal and ventral nerve cords which are connected by commissures. It controls mainly movement and some sensory functions, such as host finding and penetration by the infective juveniles and locating the females for mating in case of the males. Females stay attached to their feeding site and have probably very limited sensory perceptions. The head region contains the main chemoreceptor sense organs, the amphids. They are cup shaped with a cavity formed by sheath cells which contains the dendrites of the amphidial neurons. In case of C. elegans the function of all 12 amphidial neurons is known in detail. They are specialized for the reception of different stimuli (Bargmann, 2006). In case of cyst nematodes or other plant pathogenic nematodes we are far away from such a detailed knowledge but we can assume that the amphids are also involved in chemoreception of different semiochemicals which might be sex pheromones or substances exuded from plant roots. Amphids also produce secretions which might contain effectors involved in the suppression of host plant defence reactions. It was also found that amphid secretions are involved in producing the feeding plug which seals the plant cell wall where the nematode inserts its stylet (Endo, 1978; Sobczak, Golinowski, & Grundler, 1999). Secretions produced in amphids might also contain avirulence proteins (see below) since it was found that one protein produced in amphids was only found in an avirulent line but not in virulent lines of the root knot nematode Meloidogyne incognita (Semblat, Rosso, Hussey, Abad, & Castagnone-Sereno, 2001). In addition to the amphids the...