Abstract
pMADS3 is a class C floral homeotic gene of petunia that is specifically expressed in stamens and carpels. Introduction of pMADS3 partial genomic sequence resulted in ectopic expression of endogenous pMADS3 (ect-pMADS3) in some transgenic petunia lines, a novel epigenetic transcriptional regulation. Inclusion of intron 2 (4 kb) in the transgene was essential to induce ect-pMADS3 phenotype. Some T1 transformants inherited the phenotype even after the transgene segregation. Two allelic pMADS3 were often differently regulated. The epigenetic regulation transmitted between alleles as in paramutation. We found that 1-kb sub-region of pMADS3 intron 2 (region II) was responsible for the ect-pMADS3 phenotype. We also found that the region II DNA was methylated in the ect-pMADS3 lines, implying a correlation between the DNA methylation and the pMADS3 ectopic expression. We discuss about the integration of conventional and epigenetic transcriptional regulations in the floral-organ specific regulation of pMADS3.
