Transgene inactivation inPetunia hybrida is influenced by the properties of the foreign gene

Abstract

Petunia mutant RL01 was transformed with maize A1 and gerbera gdfr cDNAs, which both encode dihydroflavonol-4-reductase (DFR) activity. The same Agrobacterium vector and the same version of the CaMV 35S promoter were used in both experiments. Transformation with the cDNAs resulted in production of pelargonidin pigments in the transformants. However, the A1 and gdfr transformants showed clearly different phenotypes. The flowers of the primary A1 transformants were pale and showed variability in pigmentation during their growth, while the flowers of the gdfr transformants showed intense and highly stable coloration. The color difference in the primary transformants was reflected in the expression levels of the transgenes as well as in the levels of anthocyanin pigment. As previously reported by others, the instability in pigmentation in the A1 transformants was more often detected in clones with multiple copies of the transgene and was associated with methylation of the 35S promoter and of the transgene cDNA itself. In the gdfr transformants, the most intense pigmentation was observed in plants with multiple transgenes in their genome. Only rarely was partial methylation of the 35S promoter detected, while the gdfr cDNA always remained in an unmethylated state. We conclude that the properties of the transgene itself strongly influence the inactivation process. The dicotyledonous gdfr cDNA with a lower GC content and fewer possible methylation sites is more 'compatible' the genomic organization of petunia and this prevents it being recognized as a foreign gene and hence silenced by methylation.

Generation of pink flower varieties from blue Torenia hybrida by redirecting the flavonoid biosynthetic pathway from delphinidin to pelargonidin

“…These results reconfirm that pelargonidin production is an effective way to change flower color toward orange or bright red, as shown previously in petunia (Elomaa et al 1995;Meyer et al 1987;Tanaka et al 1995;Tsuda et al 2004), tobacco (Nakatsuka et al 2007), and Osteospermum (Seitz et al 2007). Our results confirm that downregulation of the F3Ј5ЈH and F3ЈH genes is insufficient and that addition of a suitable the proper DFR gene is necessary to generate a metabolic flux toward pelargonidin.…”

“…intense flower color than the maize gene in petunia (Elomaa et al 1995). Downregulation of the F3ЈH gene and expression of the rose DFR gene in red petunia accumulating cyanidin results in an orange petunia producing pelargonidin (Tsuda et al 2004).…”

“…The pelargonium DFR gene is a useful molecular tool to engineer pelargonidin-accumulating plants. The gerbera DFR gene is more efficient than the maize DFR for pelargonidin accumulation in petunia (Elomaa et al 1995). Selection of a suitable plant as a gene source is also important for successful redirection of a pathway.…”

Pathogen-induced expression of a cecropin A-melittin antimicrobial peptide gene confers antifungal resistance in transgenic tobacco

“…Similar correlation is observed in plants where the win3.12T promoter directed the expression of the GUS reporter gene (Yevtushenko et al, 2004). Other reports have shown that transgene copy number can have positive (Gendloff et al, 1990;Elomaa et al, 1995), negative (Finnegan and McElroy, 1994), or no effect (Peach and Velten, 1991) on transgene expression. Although an increased copy number has often been associated with transgene silence (for review see Finnegan and McElroy, 1994), the highest number of transgene insertions in plants in this study had no inhibitory effect on the accumulation of CEMA transcripts.…”

Expression analysis of dihydroflavonol 4-reductase genes in Petunia hybrida

“…The petals and anthers of the resultant transgenic petunia plants were salmon pink and contained pelargonidin (Tanaka et al, 1995). Elomaa et al (1995) concluded that the properties of the transgene itself strongly influenced the inactivation process.…”