Flower color modification through co-overexpression of the VtF3′5′H and RhNHX genes in Rosa hybrida

Roses ( Rosa hybrida ) are a highly merchandised flower but lack blue varieties. Overexpression of the flavonoid 3′,5′-hydroxylase ( F3′5′H ) gene can increase the accumulation of blue pigment (delphinidin anthocyanin). However, sometimes the effect of F3′5′H gene alone is inadequate for producing blue flowers. Furthermore, the internal environment of the cell, such as an increase in pH, can also help the conversion of anthocyanins to blue pigments. Nonetheless, genetic engineering methods can simultaneously introduce multiple genes at the same time to regulate the development of blue pigments to achieve the ultimate breeding goal of producing blue color in roses. In the present study, to simultaneously adjust the accumulation of delphinidin and vacuolar pH, we introduced the Viola tricolor flavonoid 3′,5′-hydroxylase ( VtF3′5′H ) and Rosa hybrida Na+/H+ exchanger ( RhNHX ) genes into the white rose line “KR056002” using Agrobacterium -mediated transformation. The quantitative real time polymerase chain reaction (qRT-PCR) results showed that the heterologous genes in the transgenic lines were highly expressed in petals and leaves, and simultaneously promoted the expression of related anthocyanin synthesis structural genes. Obvious color changes were observed in both petals and young leaves, especially when petals changed from white to red-purple. The formation of delphinidin was not detected in the petals of control plants, whereas the petals of transgenic lines had higher delphinidin content (135–214 μg/l) and increased pH value (0.45–0.53) compared with those of control plants. Key message The introduction of heterologous VtF3′5′H and RhNHX genes into rose plants can affect the flower color by regulating the expression of anthocyanin synthesis pathway genes and internal cellular mechanisms.