Isolation and Characterization of a Microsporocyte-Specific Gene, OsMSP, in Rice

A spikelet-specific cDNA clone, OsMSP (Oryza sativa meiosis serine protease), was isolated from a rice cDNA library constructed by suppression subtraction hybridization (SSH). Its expression level was significantly reduced in the thermo-sensitive genic male-sterile rice line at sterile temperature (30/26°C, day/night) compared with that at fertile temperature (23/21°C, day/night) conditions. In contrast, no significant differences were observed in the normal fertile line under the above two sets of temperature conditions. The cDNA is 2,867 bp in length with an open reading frame (ORF) encoding 837 amino acid residues. Northern blots revealed that OsMSP transcripts were specifically present in spikelets at meiosis, and reached the highest level at early microspore stage. mRNA in situ hybridization confirmed that OsMSP was a rice microsporocyte-specific gene and its expression was limited to early microspore developmental stage. BLAST and phylogenetic analyses revealed that OsMSP shared high similarities with subtilisin-like serine protease genes from other organisms at both nucleotide and amino acid levels.