Genetic analysis in rice of disease resistance to Magnaporthe grisea

J.B. Morel, S. Alidor, D. Arnal, N. Atoui, V. Chalvon, S. Gaillard, C. Loussert, G. Mascre, E. Vergne, M.H. Lebrun, D. Tharreau, J.L. Nottéghem
INRA-CIRAD-ENSAM Centre de Montpellier, UMR BGPI CIRAD TA 40/02, Avenue d'Agropolis - 34398 Montpellier Cedex 05

In contrast to dicots, only a few genetic regulators of disease resistance in Monocots have been identified. Our goal is to dissect and identify general regulators of resistance to rice blast (caused by Magnaporthe grisea). For this purpose, GUS and GFP enhancer trap T-DNA rice lines (produced in the Génoplante programs) are screened for altered susceptibility to a virulent isolate of M. grisea (~200 lines/week). Three main phenotypes are selected: enhanced disease resistance (EDR), enhanced disease susceptibility (EDS) and lesion simulating disease (LSD). In addition to this visual screening, GUS induced enhancer traps have been detected. From more than 8000 lines screened, 105 show altered susceptibility (1.5%) and most lines display phenotypes typical of enhanced resistance. When assayed, the mutant lines also show altered resistance to different isolates of M. grisea, suggesting that the identified mutations affect central steps of the disease resistance transduction pathway. Using a high throughput DNA procedure, the identified mutants are subsequently mass-genotyped for the T-DNA insertion as well as for the Tos17 retrotransposon which is activated during the transformation steps. Based on this analysis, it appears that separate insertion lines are probably deriving from the same cell multiplied in vitro (clonal events). This analysis also showed that for 35 lines analyzed, 11 are not tagged by either the T-DNA nor new insertions of Tos17. In a separate screen, enhancer trap lines responsive to methyl jasmonate and/or salycilate, two know signaling molecules, are detected. Further biological and molecular analysis of the différent lines will be presented.











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