[Cloning of a rice male sterility gene by a modified MutMap method]

A pollen defective male sterile rice mutant, osms55, was isolated from an elite indica cultivar HHZ using EMS (ethyl methanesulfonate) mutagenesis strategy. Genetic analysis showed that osms55 was controlled by a single recessive gene. Genome-wide SNP analysis using the high-throughput Illumina Infinium iSelect SNP (50 K) microarray technology indicated that the genetic makeup of osms55 is the same as wild type (WT) HHZ. Using a modified MutMap method, we successfully identified a mutation in the LOC_Os02g40450 (MER3) gene that is co-segregated with the male sterility phenotype. The mutation is located at the intron splice-recognition site, leading to a 15 nucleotide deletion in the fifth exon. Different from the published MutMap method that aligns the mutant pool DNA sequence with the assembled WT genome, the method used in this study was to align the re-sequencing data of the mutant pool DNA and WT HHZ with the Nipponbare reference genome. The resulting SNPs of mutant/Nipponbare and WT HHZ/Nipponbare were further compared to determine the candidate mutant gene. This modified method does not need an assembled WT genome as reference and thus is more cost-effective and widely applicable.