Progeny of @entity286 line 2853.6, which carries a @entity3639 phosphotransferase (SPT) gene interrupted by the @entity2829 element Activator (Ac), were selected for @entity3639 resistance (Spr) because of germinal Ac excision. Some events gave rise to Spr alleles that were unstable and exhibited a mottled phenotype on @entity3639 -containing medium due to somatic loss of SPT function. This instability was most pronounced in one particular line, Spr12F. Other Spr alleles rarely exhibited silencing of SPT. @entity3639 -sensitive, homozygous Spr12F plants were recovered, and crosses were performed with other, more stable Spr lines. A high proportion of the resulting heterozygous progeny were silenced for SPT expression. The silenced state was heritable even after the Spr12F allele segregated away. No correlation could be made between silencing and methylation of the SPTgene. Structural analysis of allele Spr12F showed that the SPT gene from which Ac had excised was flanked by direct repeats of Ac. A search was carried out among 110 additional Spr alleles for new independent unstable alleles, and four were identified. All of these alleles also carried an SPT gene flanked by direct repeats of Ac. Thus, there is a strong correlation between this structure and instability of SPT expression.

Epigenetic instability and trans-silencing interactions associated with an SPT::Ac T-DNA locus in XXXX .

@entity3639 :: ('MESH:D013307', 'Chemical') :: ['streptomycin', 'Streptomycin'] @entity286 :: ('4097', 'Species') :: ['tobacco'] @entity2829 :: ('4577', 'Species') :: ['maize']
@entity286 :: (4097,Species) :: ['tobacco']
