A rice spotted leaf gene, SpI7, encodes a heat stress transcription factor protein

A rice spotted leaf (lesion-mimic) gene, SpI7, was identified by map-based cloning. High-resolution mapping with cleaved amplified polymorphic sequence markers enabled us to define a genomic region of 3 kb as a candidate for SpI7 We found one ORF that showed high similarity to a heat stress transcription factor (HSF). Transgenic analysis verified the function of the candidate gene for SpI7: leaf spot development was suppressed in spI7 mutants with a wild-type SpI7 transgene. Thus, we conclude that SpI7 encodes the HSF protein. The transcript of spI7 was observed in mutant plants. The levels of mRNAs (SpI7 in wild type and spI7 in mutant) increased under heat stress. Sequence analysis revealed only one base substitution in the HSF DNA-binding domain of the mutant allele, causing a change from tryptophan to cysteine.