Twin Sectors caused by Alternative Transpositions in Maize
During development of the maize ear, mutations may occur during cell division. These mutations can form twin sectors, or a sector of the maize ear that has a different coloration or pattern in the pericarp, seed coat, of the maize ear.
We studied the effects of Activator (Ac) transposon (a chromosomal segment that can undergo transposition) in the development of twin sectors on maize ears containing the allele P1-ovov454. This allele conditions orange-variegated pericarp and cob due to the presence of the Ac transposon in the p1 gene which controls kernel pericarp color. We screened for ears with multi-kernel dark red/orange sectors twinned with sectors of colorless pericarp. From this visual screen, we identified 6 different twin sectors on two maize ears. A series of screening PCR tests were developed to classify the type of structural changes present in each case. Then the junctions of the Ac transposon and flaking DNA were amplified by PCR and sequenced. Based on the results, we determined the structure of each new allele and proposed a mechanism of origin for most cases. Some were formed by simple Ac transposition, while others were generated by more complex recombination events.
These findings showed that twin sectors develop in parallel with adjacent sectors, in addition to demonstrating how gene structure and gene expression can be altered by the Ac transposable element during ear development.