Articles
BIOLOGICAL FEATURES, POSITIONAL CLONING AND FUNCTIONAL VALIDATION OF THE MA GENE FOR COMPLETE-SPECTRUM RESISTANCE TO ROOT-KNOT-NEMATODES IN PRUNUS
Article number
1084_2
Pages
33 – 38
Language
English
Abstract
Stone fruit crops Prunus spp. grown under Mediterranean climates are severely damaged by root-knot nematodes (RKN) Meloidogyne spp.
Breeding for RKN resistant-rootstocks is a promising control alternative to nematicide ban.
Resistance (R) genes have been identified and mapped in plums (Ma and Rjap), peach (RMia) and almond (RMja). Among those genes, Ma from Myrobalan plum has been shown to confer a complete-spectrum, high-level and heat-stable resistance to both mitotic (M. arenaria, M. incognita, M. javanica and M. enterolobii) and meiotic (M. floridensis) RKN. The Ma gene triggers a hypersensitive-like reaction (HLR) characterized by the total absence of galls.
In plants carrying Ma, nematode attacks induce the development of subterminal lateral rootlets replacing primary terminal apices and providing an active resistance response to HLR damage.
Sustainability of resistance conferred by Ma has been challenged in multi-year experiments applying a high and continuous nematode inoculum pressure by co-cultivation of RKN-infested susceptible tomato plants together with Prunus plants carrying Ma or, for comparison, with R tomato plants carrying the Mi-1 reference gene.
Galling and virulent nematode individuals have been observed in Mi-1 resistant tomatoes but not in Ma-carrying Prunus plants.
High resolution mapping from over 3000 segregants for the positional cloning of the Ma locus in accession P.2175 showed that Ma belongs to a cluster of three TIR-NB-LRR genes (TNL1 to TNL3) including a pseudogene (TNL2) and a truncated gene (TNL3). Using A. rhizogenes transformed hairy roots and composite plants, the candidate gene TNL1, comprising the genomic sequence preceded by its native promoter region (15.3 kb), has been functionally validated as Ma as it conferred the same complete-spectrum and high-level resistance as in the donor clone P.2175. The full-length cDNA (2048 deduced aa) of Ma is the longest of all R genes cloned to-date due to its huge C-terminal post-LRR (PL) region.
Breeding for RKN resistant-rootstocks is a promising control alternative to nematicide ban.
Resistance (R) genes have been identified and mapped in plums (Ma and Rjap), peach (RMia) and almond (RMja). Among those genes, Ma from Myrobalan plum has been shown to confer a complete-spectrum, high-level and heat-stable resistance to both mitotic (M. arenaria, M. incognita, M. javanica and M. enterolobii) and meiotic (M. floridensis) RKN. The Ma gene triggers a hypersensitive-like reaction (HLR) characterized by the total absence of galls.
In plants carrying Ma, nematode attacks induce the development of subterminal lateral rootlets replacing primary terminal apices and providing an active resistance response to HLR damage.
Sustainability of resistance conferred by Ma has been challenged in multi-year experiments applying a high and continuous nematode inoculum pressure by co-cultivation of RKN-infested susceptible tomato plants together with Prunus plants carrying Ma or, for comparison, with R tomato plants carrying the Mi-1 reference gene.
Galling and virulent nematode individuals have been observed in Mi-1 resistant tomatoes but not in Ma-carrying Prunus plants.
High resolution mapping from over 3000 segregants for the positional cloning of the Ma locus in accession P.2175 showed that Ma belongs to a cluster of three TIR-NB-LRR genes (TNL1 to TNL3) including a pseudogene (TNL2) and a truncated gene (TNL3). Using A. rhizogenes transformed hairy roots and composite plants, the candidate gene TNL1, comprising the genomic sequence preceded by its native promoter region (15.3 kb), has been functionally validated as Ma as it conferred the same complete-spectrum and high-level resistance as in the donor clone P.2175. The full-length cDNA (2048 deduced aa) of Ma is the longest of all R genes cloned to-date due to its huge C-terminal post-LRR (PL) region.
Publication
Authors
D. Esmenjaud, C. Van Ghelder, J. Polidori , S. Khallouk, H. Duval
Keywords
major gene, resistance, root-knot nematode, positional cloning, Prunus
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