Identification and characterisation of broad spectrum disease resistance mutants in Arabidopsis

Activation tagging was employed in conjunction with the reporter gene line PR-1::LUC to uncover novel systemic acquired resistance (SAR) mutants. The mutant screen employed imaging for constitutive LUC expression or the absence of LUC expression after induction with the salicylic acid (SA) functional analogue, benzo (1,2,3) thiadiazole (BTH). A set of three mutants displaying constitutive LUC activity were selected for further characterisation. These mutants were subsequently named activated disease resistance 2,3 and 6 (adr2, adr3 and adr6), and showed constitutive PRI expression. Furthermore, all three mutants were resistant to the virulent oomycete pathogen Peronospora parasitica Noco2 and adr3 to the virulent bacterial pathogen Pseudomonas syringae pv. Tomato (DC3000). Genetic and molecular analysis indicated that two of these mutants were not tagged (adr2, adr6) and that plasmid rescue of adr3 gene was not a straightforward technique, therefore cloning was attempted using a map-based approach, adr2 maps to chromosome 5, whereas adr3 and adr6 map to chromosomes 4 and 1 respectively. Genetic analysis indicated that adr2 and adr6 are recessive mutations and define single genes. Although adr3 maps as a single mutation, its mode of inheritance is yet unidentified. Double mutants were produced between adr mutants and SA-, JA- and ET- insensitive mutants. Epistasis analysis and mapping data suggest that the adr mutants define three novel loci. Therefore they will provide new genetic tools for dissecting broad-spectrum resistance mechanisms.