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

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.