A new P-ww allele and Ac element with high negative dosage effect and novel suppressing activity
--Jianbo Zhang and Thomas Peterson

A new P gene allele (P-ww*-12:27-3) which specifies colorless pericarp and cob glumes was derived in two steps from P-ovov-1114. The P-ww*-12:27-3 allele carries an Ac element with a very high negative dosage effect. In crosses to P-vv and the Ac tester line r-m3, both Ac transposition in pericarp and Ds excision in aleurone occurred very late. Also, P-ww*-12:27-3 suppresses the orange pericarp pigmentation specified by P-ovov-1114 (which carries Ac inserted in the P-rr intron 2) and two other P gene alleles carrying Ds elements. Thus, P-ww*-12:27-3 suppresses the expression of Ac- and Ds-induced alleles, similar to the Suppressor function of the En/Spm transposon system. Preliminary Southern blot analysis indicates that P-ww*-12:27-3 has a duplication of part of the P gene. Further molecular studies are in progress to determine what molecular changes occurred to generate the novel Ac element in P-ww*-12:27-3 from the standard Ac in P-ovov-1114.
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