Frequent loss of the En transposable element after excision and its relation to chromosome replication in maize (Zea mays L.).

A model of En transposition during chromosome replication is presented following a study of somatic events associated with the transposition of En in the endosperm tissue of the maize kernel. Two supporting assays, the excision and the postexcision events, were used in following these events. The excision of the En transposon has been monitored in the starch-producing endosperm tissue by using the wx-844 autonomously mutable allele, and events after excision have been monitored by using various reporter alleles of the En-1 (Spm-dSpm) system. The initial observations revealed an unusually large amount of loss of the En transposon following its excision from the wx-844 allele. Subsequent analysis of the somatic events using the a2-m1 reporter allele to monitor the dosage of En suggested that the large amount of loss would result from the transposition of En during chromosome replication. Transposition of En from a replicated segment of the chromosome to another site that has also undergone replication explains most of the somatic events observed.