SOMATIC INACTIVATION AND REACTIVATION OF AC ASSOCIATED WITH CHANGES IN CYTOSINE METHYLATION AND TRANSPOSASE EXPRESSION

Several metastable Ac alleles at the maize p locus were identified tha t produced novel pericarp variegation patterns. From the transmission analysis of pericarp sectors, we show that Ac inactivation is a somati c process. Ac excision from P and transactivation of an unlinked Ds wa s delayed or absent in plants with metastable Ac alleles. These decrea ses in Ac activity were correlated to increases in cytosine methylatio n at specific sites near the start of Ac transcription (open reading f rame a; ORFa) and at sites in some flanking P sequence. Reactivation o f inactive alleles was accompanied by decreased methylation of A c and P sequences. Using a competitive polymerase chain reaction assay, ste ady state levels of ORFa transcript were quantitatively compared among the various metastable alleles. We propose that changes in the methyl ation profile of Ac correspond to changes in Ac activity through the d ifferential accumulation of Ac transcript.