The genetics of variable states of the En controlling element system in Zea mays L.
Controlling elements insert into gene loci and interrupt the functioning of genes. The gene function is restored when the element is excised from the locus. In a developing maize kernel, such restoration of gene activity for anthocyanin production results in a spotted aleurone phenotype where each colored spot represents a single mutational (excision) event. Th spots vary in size and number depending on the timing and frequency of excisions;In the En(Spm)-I two-unit controlling element system, the excisions of the receptor element I are triggered by the regulatory element En(Spm). The resulting spotted pattern, as defined by the size and frequency of spots, depends on the state of these elements;In this study, changes in state I and En(Spm) are investigated among mutable alleles a-m-1 5719A-1, a-m-1 5996-4, a-m-1 6078, a-m-2 7977B and a-m-2 8004. The putative changes in state are identified and confirmed by appropriate genetic crosses;Several changes in state of I and En(Spm) are confirmed in each of the five mutable cultures. The new states of I differed in their response to En(Spm) and/or in their basic allele phenotype (-En or Spm). Among a-m-2 7977B cultures, a unique change in state of I discriminated En from Spm which otherwise are functionally similar;The new states of En or Spm arose as a result of changes from an active to another active state or to an inactive state. In some cases, however, reversions to the original state occurred, indicating that they are changes in phase of activity;In addition to these changes in state, some unusual phenotypes appeared among a-m-1 5719A-1, a-m-1 5996-4 and a-m-1 6078 cultures. These phenotypes and their inheritance patterns suggest novel gene control mechanisms.