Family HETERODERIDAE

                                   Rev. 10/14/23

Classification:

      Tylenchida
       Tylenchina
        Tylenchoidea

         Heteroderidae Filip'ev & Schuurmans Stekhoven, 1941
   

Synonyms:
      Meloidogynidae (Skarbilovich, 1959)
      Meloidoderidae (Golden, 1971)
      Ataloderidae (Wouts, 1973)

Nematode genera in the family Heteroderidae can be divided into two major groups: the cyst nematodes in which the famale body becomes a hard-walled cyst, and the cystoid nematodes in which the body wall of the female does not harden (Subbotin et al., 2017).

Cyst Nematodes	Cystoid Nematodes
Afenestrata (=Heterodera)	Atalodera
Betulodera	Bellodera
Cactodera	Camelodera
Globodera	Cryphodera
Heterodera	Ekphymatodera
Punctodera	Hylonema
Vittatidera	Meloidodera
	Rhizonemella
	Sarisodera
	Thecavermiculatus (=Atalodera)
	Verutus

Morphology and Anatomy:

• Sedentary obligate parasites of roots, forming galls in some cases.
• Marked sexual dimorphism, body vermiform and slender in second-stage juveniles, robust in males, and inflated in females.  Labial region and cephalic framework well developed, especially in males and juveniles, secondarily reduced in females. 
• Stylet robust; cone half the length of total stylet. 
• Dorsal esophageal gland opening close to base of stylet. 
• Median esophageal bulb usually large, with strong valves. 
• Esophageal glands overlapping intestine ventrally and also laterally. 

Female:

• Sedentary in root tissues.
• Globose (exception: Verutus with sausage-shaped females). 
• Vulva generally terminal or subterminal (exception: Verutus and Meloidodera where equatorial).  Two genital branches, amphidelphic or prodelphic.  Columned uterus with three rows of cells.
• Eggs laid in a gelatinous matrix (exception: Verutus) or totally or partially retained within female body of which the cuticle may be transformed (cysts). 

Male:

• Vermiform.  Metamorphosis within juvenile cuticle (exception: Verutus). 
• No caudal alae (exception: Bursadera). 
• Tail short or absent. 

Second stage juveniles:

• Tail conical, with long hyaline posterior part. 
• Phasmids anterior to half tail length.

Two sub-families:

General Characteristics of cyst nematode genera

Feeding:

Large sectors of the developing root, including areas that would have become vascular tissue are transfomed into syncytia (Heteroderinae) or giant cells (Meloidogyninae).  Syncytia and giant cells have many plastids, mitochondria, ribosomes, increased rough endoplasmic reticulum and enlarged lobed nuclei. 

Cell wall protruberances increase the surface area of the cell membrane for flow of solutes from the xylem to the syncytium - the transfer cell configuration (Endo, 1975).

More than 50 genes are upregulated to some extent in the development of giant cells (Meloidogyne) and syncytia (Heterodera/Globodera) (Gheysen and Fenoll, 2002). Both types of feeding cells have the genome amplified as a result of multiple shortened cell cycles; but the processes differ. Giant-cells go through repeated (acytokinetic) mitosis.  Syncytia undergo repeated S-phase endoreduplication without mitosis or nuclear division. 

The eukaryotic cell cycle has four stages.: 1. Nuclear DNA is replicated during synthesis phase (S-phase). 2. DNA synthesis is followed by an interval called the G2 phase (G=gap). 3.  Mitosis occurs, the nucleus divides (M-phase). 4.  The interval between the completion of mitosis and the beginning of DNA synthesis is the G1-phase,  In normal cell division, the cell divides (cytokinesis) after the mitosis phase. In the root-knot nematode (Meloidogyne) feeding site there is repeated nuclear division (S and M phases of the cell cycle) but no cell division; this is called acytokinetic mitosis or karyokinesis without cytokinesis. In the cyst nematode (Heterodera, Globodera) feeding site, the S phase of the cell cycle is activated but not the M phase.   Instead, the cells repeatedly go through the S-phase (endoreduplication) and probably through parts of the  G1 and G2 phases, but bypass mitosis.

The Cell Cycle:  modified from Gheysen and Fenell, 2002.

Since nematodes in the Heteroderidae become sedentary from the late second stage onwards (except for the metamorphosis to males), the feeding site in the plant must be maintained in a condition favorable for perhaps five or six weeks to allow the nematode to fulfill its reproductive potential.  Besides stimulation of the cell cycle events, pathogen-triggered immunity (PTI) responses, including activation of the salicylic acid pathway, must be suppressed. The salicylic acid pathway leads to production of active oxygen molecules and hypersensitive cell death.  In the Meloidogyninae, a possible candidate for effector-triggered suppression of PTI is chorismate mutase, produced in the nematode esophageal glands.  In PTI responses, chorismate is converted to salicylic acid to iniate the defense events.  Chorismate mutase from the nematode reduces chorismate, and thus salicylic acid (Smant and Jones, 2011). In Heteroderinae, the Hg30C02 effector protein of Heterodera glycines may be involved in active suppression of host defenses. The same gene occurs in H. schachtii but not in Meloidogyne spp. (Hamamouch et al., 2012).

As of 2013, some 70 proteins, many new or unknown, have been detected in nematode secretions into plant cells (Thomas Baum, pers. com.)

References:

• Gheyson, G. and C. Fenoll.  2002. Gene expression in nematode feeding sites.  Ann. Rev. Phytopathol. 40: 191-219.

• Luc, Maggenti & Fortuner, Rev. Nematol. 11:159-176 (1988)
• H. Ferris
• Hamamouch, N., Li, C., Hewezi, T., Baum, T.J., Mitchum, M.G., Hussey, R.S., Vodkin, L.O., Davis, E.L. 2012.  The interaction of the novel Hg30C02 cyst nematode effector protein with a plant b-1,3-endoglucanase may suppress host defence to promote parasitism.  Journal of Experimental Botany.
• Smant, G., Jones, J. 2011.  Suppression of plant defences by nematodes.  Chapter 13, pp 273-286. In Jones, J., Gheysen, G., Fenoll, C. (eds).  Genomics and Molecular Genetics of Plant-Nematode Interactions.  Springer, NY.
• Subbotin, S.A., Jerry Akanwari, Chau N. Nguyen, Ignacio Cid del Prado Vera, John J. Chitambar, Renato N. Inserra and Vladimir N. Chizhov. 2017. Molecular characterisation and phylogenetic relationships of cystoid nematodes of the family Heteroderidae (Nematoda: Tylenchida). Nematology 19:1065-1081.

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