Improved leaf and flower longevity by expressing the etr1-1 allele in Pelargonium zonale under control of FBP1 and SAG12 promoters

Abstract

The ethylene receptor etr1-1 (ETHYLENE RESPONSE 1) mutant gene from Arabidopsis thaliana, with its expression under the control of either the Petunia floral binding protein FBP1 promoter or the Arabidopsis senescence-specific SAG12 gene promoter, was introduced into Pelargonium zonale cv. ‘Katinka’. The heterologous expression of these transgenes and the response of flowers and leaves to exogenous ethylene were then studied. Transgenic etr1-1 lines grown in the greenhouse did not differ morphologically or physiologically from nontransformed plants nor was the rooting ability of cuttings affected. Reverse transcription (RT)-PCR revealed that transcripts from an FBP1 promoter were present from green tissue to the roots, whereas the SAG12 promoter was only active in processes associated with aging or senescence of flower petals and leaves. The sensitivity to ethylene exposure was markedly reduced by using both promoter constructs. Flower petals from nontransformed controls were fully senescent 4 days after ethylene exposure, while more than 90% of the flower petals from FBP1-promoter lines and over 50% of the flower petals from SAG12-promoter lines remained unchanged, without showing any signs of wilting or any response to ethylene. However, ethylene sensitivity of leaves was only delayed in the best lines but not suppressed through etr1-1 expression. Foliage displayed less intense leaf yellowing and wilting, which were similar for both promoter variants compared to wild type controls.