Figure 10.
Schematic model for molecular mechanisms of dominance relationships at the pollen side. (A) In the case where S1 is dominant over S2, dominant transcripts of SP11, S1-SP11, are specifically expressed in the S1S2 heterozygote. However, S2-SP11 transcripts are not detected in the S1S2 heterozygote on RNA gel blot analysis. The results demonstrate that the dominance relationship at the pollen side is regulated at the transcriptional level. (B) In the dominant S allele, small RNA, termed Smi (SP11 methylation inducer), is specifically produced, and its nucleotide sequence is highly similar to the promoter region of the recessive SP11 gene. This small RNA induces the methylation of recessive SP11, and represses the recessive SP11 at the transcriptional level.