Expression profiling of a lesion mimic genotype, splNF4050-8, that confers blast resistance in rice

Lesion mimic mutants in rice are widely known as spotted leaf (spl) mutants, of which several genotypes exhibit enhanced resistance to different races of Magnaporthe grisea. Besides naturally occurring spotted leaf mutants, tissue culture-induced reverse genetic repositories also act as sources of lesion mimic mutants in rice. We systematically evaluated a large collection of Tos17 mutant panel lines, developed and maintained at the National Institute of Agrobiological Sciences, Tsukuba, Japan, for their reaction to three different races of M. grisea and identified a lesion mimic mutant, NF4050-8, that showed lesions similar to naturally occurring spl5 mutant and enhanced resistance to all three blast races tested. Microarray analysis of ~44,000 rice genes in NF4050-8 with Nipponbare as control during the progressive lesion appearance stage revealed significant up-regulation of numerous defense/pathogenesis-related genes as well as several WRKY domain-containing genes and down-regulation of haem peroxidase gene. Subsequent real-time PCR analysis of WRKY45 and PR1b genes in NF4050-8 and spl5 suggested possible constitutive activation of a defense signaling pathway downstream of Salicylic Acid (SA) but independent of NH1 in these mutant lines of rice. Overall design: We used Agilent rice oligo microarrays to identify putative defense/pathogenesis-related genes. Leaf tissues of the rice genotypes Nipponbare and NF4050-8 were used in the study. Two replications of microarray experiments were carried out by hybridizing the cRNA from control and progressive lesion appearance stage on 4 x 44k microarray.