Table 3.
Examples of repeat-containing protein (RCP) effectors from plant-associated nematodes and insects.
| RCP (aaa) | Plant-associated organism | Host plant (relationship with host) | Repeat featuresb | Localization in planta | Part of an RCP effector family? | References |
|---|---|---|---|---|---|---|
| Gp-HYP (variesc) | Globodera pallida (plant-parasitic nematode) | Solanaceae (sedentary endoparasite of plant roots) | Three Gp-HYP effector subfamilies (Gp-HYP-1, Gp-HYP-2, and Gp-HYP-3) containing a various number of hydrophilic perfect and imperfect tandem repeats of 5–17 aa | Host apoplast | Yes | Eves-van den Akker et al., 2014 |
| Biological function: Gp-HYP effectors contribute to G. pallida parasitism, although their specific functions are unknown | ||||||
| GrCLE1 (204) | Globodera rostochiensis (plant-parasitic nematode) | Solanaceae (sedentary endoparasite of plant roots) | Four hydrophilic imperfect CLAVATA3 (CLV3)/endosperm surrounding region (ESR) (CLE)-like motif repeats of 12 aa (three identical), separated by a hydrophilic imperfect spacer repeat of 9 aa | Host apoplast | Yes | Lu et al., 2009; Guo et al., 2011; Chen et al., 2015 |
| Biological function: GrCLE1 is processed into at least three arabinosylated CLE-like peptides by host proteases. These CLE-like peptides directly bind plant receptor-like kinases (RLKs), including CLV2, BAM1, and BAM2, where they function as endogenous plant CLE peptide mimics to incite changes in plant root growth and development that facilitate parasitism | ||||||
| MAP (variesc) | Meloidogyne incognita (plant-parasitic nematode) | Broad host range (sedentary endoparasite of plant roots) | Up to nine hydrophilic imperfect CLE-like motif repeats of 14 aa. A hydrophilic imperfect Heterodera variable domain-like motif (HVLM) repeat of 15 aa is often interspersed between CLE-like motifs | Host apoplast | Yes | Semblat et al., 2001; Castagnone-Sereno et al., 2009; Vieira et al., 2011; Rutter et al., 2014 |
| Biological function: MAP effectors are possibly processed into CLE-like peptides that function as mimics of endogenous plant CLE peptides. These peptides then possibly interact with cognate host RLKs to incite changes in plant root growth and development that facilitate parasitism. HVLM repeats may function in the trafficking of MAP effectors into the host apoplast, the processing of MAP effectors to mature CLE-like peptides, and/or host specificity. MAP-1 may be recognized by the Mi-1 immune receptor of tomato, with the number/arrangement of repeats in MAP-1 correlated with avirulence of M. incognita | ||||||
| MpC002 (265) | Myzus persicae (aphid; plant pest) | Broad host range (phloem feeder) | Five hydrophilic perfect tandem repeats of 7 aa | Host vascular tissue (phloem)? | No | Bos et al., 2010; Pitino et al., 2011; Pitino and Hogenhout, 2013; Elzinga et al., 2014 |
| Biological function: MpC002 increases M. persicae fecundity on Arabidopsis thaliana, Nicotiana benthamiana, and Nicotiana tabacum through an unknown mechanism. The repeat domain is required for this increased fecundity | ||||||
| SSGP-71 (variesc) | Mayetiola destructor (Hessian fly; plant pest) | Cereals (gall-forming pest) | Typically 13 amphipathic degenerate tandem leucine-rich repeats (LRRs) of ~20–30 aa | Likely intracellular (host) | Yes | Zhao et al., 2015 |
| Biological function: SSGP-71 effectors typically contain an amino (N)-terminal cyclin-like F-box, followed by carboxyl (C)-terminal LRRs. These effectors, which interact with host Skp proteins, are suspected to mimic host F-box-LRR proteins in order to hijack the plant proteasome for the purpose of directly producing nutritive tissue, defeating plant immunity, and/or stunting plant growth. The LRR domain of SSGP-71 effectors is expected to provide target (host protein) specificity. The SSGP-71 effectors Mdes009086-RA and Mdes015365-RA are recognized by the H6 and H9 immune receptors of wheat, respectively. Unlike Mdes009086-RA, Mdes015365-RA does not possess an F-box | ||||||
| vH13 (116) | M. destructor | Three hydrophilic imperfect tandem repeats of 12 or 14 aa | Unknown | No | Aggarwal et al., 2014 | |
| Biological function: vH13 function unknown. vH13 is recognized by the H13 immune receptor of wheat | ||||||
a
Protein length in amino acids (aa).
b
Repeat hydropathy profiles were determined using the Expasy ProtScale server (http://web.expasy.org/protscale/), with default server settings.
c
The protein length varies between members of the RCP effector family.