Epigenetic floral homeotic mutation in pD991-AP3-derived T-DNA-tagged lines for CTP:Phosphorylcholine cytidylyltransferase (CCT) Genes: The homeotic mutation of the cct1-1 allele is enhanced by the cct2 allele and alleviated by CCT1 overexpression

The apetala3 (ap3)-like homeotic mutation (ap3-HM) is recognized among pD991-AP3-derived Arabidopsis thaliana T-DNA-tagged lines carrying the -448 to +47 region of AP3 in their T-DNA. In the corresponding mutant lines for CTP:phosphorylcholine cytidylyltransferase genes, cct1-1 and cct2 (Inatsugi et al. 2009), some flowers of cct1-1 (F4) and many flowers of cct1-1 cct2 (F3) showed ap3-HM, and all flowers of cct1-1 (F5) and cct1-1 cct2 (F4) became increasingly homeotic. In contrast, cct2 flowers were normal for all generations tested. These results demonstrated that ap3-HM is linked to the cct1-1 allele and is enhanced by the cct2 allele. The ap3-HM in cct mutants was inversely correlated with AP3 transcript levels in enriched flower buds. Bisulfite sequencing revealed severe methylation within endogenous AP3 promoter regions in cct1-1 (F3; -317 to -2) and cct1-1 cct2 (F3; -473 to -2), but wild-type (Wassilevskaja) and cct2 plants showed no corresponding methylation. The ap3-HM in cct1-1 cct2 mutants was fully rescued by expressing a PISTILLATA promoter–AP3 construct, and was better alleviated in the F₁ offspring of a cross with the CCT1-overexpressing mutant cct1-2 (Columbia) than with the wild type. We discuss possible links between expression of CCT and suppression of ap3-HM.