Instability of the Arabidopsis mutant csn5a-2 caused by epigenetic modification of intronic T-DNA.

T-DNA insertion mutants play a crucial role in elucidating Arabidopsis gene function. In some cases, two or more T-DNA mutants are combined to study genetic interactions between homologous genes or genes hypothesized to act in the same pathway. We studied the significance of protein–protein interactions between CSN5A and ROP11 by crossing three independent rop11 T-DNA insertion mutants with csn5a -2, a partial loss-of-function intronic T-DNA insertion mutant. The csn5a-2 single mutant is severely stunted, but double rop11 csn5a-2 mutants were rescued and exhibited increased CSN5A transcript and protein levels. The rescued phenotype was maintained in non-Mendelian fashion when the csn5a-2 single mutant was re-isolated from the rop11-1 csn5a-2 double mutant, and was sensitive to two inhibitors of DNA methylation. Loss of kanamycin resistance was also observed in re-isolated csn5a-2 . These findings indicate that the rescue of csn5a-2 resulted from a trans T-DNA-mediated epigenetic effect on the csn5a-2 intronic T-DNA, similar to recent reports involving the intronic T-DNA mutants ag-TD , ben1-1 , and cob-6 . Thus the work reported here provides further support for the recommendation that mutants created through novel combinations of T-DNA alleles should be carefully evaluated for evidence of epigenetic modification of T-DNA before final conclusions are drawn. [ABSTRACT FROM AUTHOR]