Modular architecture and evolution of the map-1 gene family in the root-knot nematode Meloidogyne incognita

Abstract

In eukaryotes, repeat proteins (i.e. proteins that contain a tandem arrangement of repeated structural elements) are often considered as an extra source of variability, and gains and losses of repeats may be an important force driving the evolution and diversification of such proteins, that could allow fast adaptation to new environments. Here, we report genomic sequences of the MAP-1 protein family from of the asexual, plant-parasitic nematode Meloidogyne incognita. The encoded proteins exhibited highly conserved repeats of 13 and 58 aa, and variation in the number and arrangement of these repeats in the MAP-1 proteins was correlated with nematode (a)virulence, suggesting a possible role in the specificity of the plant-nematode interaction. Search in the complete genome sequence of M. incognita confirmed that a small gene family encoding proteins harboring conserved 58 and 13 aa-repeats is present in this nematode, and that the repetitive region of these proteins is modular. Both gene duplication and intragenic gain and loss of repeats have contributed to the complex evolutionary history of the map-1 gene family, and active selection pressure of the plant host probably induced recent additional gene loss, finally resulting in the present-day gene and repeat diversity observed among nematode lines. The genomic differences characterized here between avirulent and virulent individuals are assumed to reflect, at the DNA level, the adaptive capacity of these asexual root-knot nematodes.

Plant-nematode Interactions: From Genomics to Metabolomics

“…For example, M. incognita secreted map-1.2 protein shows specifically increased expression in Mi-1 resistant tomato lines. It suggests that the map-1.2 might be a putative avirulent (Avr gene) response to Mi gene (Castagnone-Sereno et al, 2009). A similar effect has been shown for H. glycines chorismate mutase (Hg-cm-1) in soybean cultivars.…”

“…A similar effect has been shown for H. glycines chorismate mutase (Hg-cm-1) in soybean cultivars. But still the plant targets for both these Avr candidate genes and their particular function are unknown (Bekal et al, 2003;Lambert et al, 2005;Castagnone-Sereno et al, 2009). However, another M. incognita gene, Cg-1, was confirmed as an Avr gene corresponding to the Mi-1 resistance gene in tomato (Gleason et al, 2008).…”

Functional roles of effectors of plant-parasitic nematodes

“…MAP-1 is a protein (whose sequence is characterised by internal repetitive motifs of 13 and 58 amino acids) secreted from the amphids in avirulent populations of M. incognita (Semblat et al, 2001). Map-1 belongs to a small gene family, specific to RKNs and only found in avirulent lines of the three Meloidogyne species that are controlled by the tomato resistance gene Mi-1 (Castagnone-Sereno et al, 2009;Semblat et al, 2001). It has been suggested that MAP-1 could be involved in early recognition steps mediated by Mi-1 and that the specificity of the plant-nematode interaction could be related to the variation in the number or arrangement of repeats in the proteins.…”

How Durable is Root Knot Nematode Resistance in Tomato?

“…2A). The best example is MAP-1, RKN effector proteins which were identified in near-isogenic lines of M. incognita selected on plants carrying Mi-1 resistance gene (Semblat et al 2001), and subsequently, showed correlation to nematode avirulence (Castagnone-Sereno et al 2009), indicating ETI response in association with the R-gene Mi-1 (Fig. 2A).…”