| Ethylene regulates seed germination (Ecker, 1995), seedling growth, leaf and petal abscission, fruit ripening and organ senescence in plants (Gamble et al., 2002). Five ethylene receptors exist in Arabidopsis thaliana, however, only two of these receptors, ETR1 and ERS1, have putative histidine-kinase domains (Gamble et al., 2002). The histidine-kinase domain is at the carboxy-terminus, while the ethylene binding domain is located at the amino-terminus (Bleeker and Kende, 2000). The etr1-1 mutant plants confer dominant ethylene insensitivity and their seeds experience difficulty in germinating (Ecker, 1995). In this project, a chimeric gene was constructed, whereby the transmembrane and GAF encoding domains of ETR1 were attached to the histidine-kinase encoding domain of ERS1. Site-directed mutagenesis was then performed on this gene to imitate the single base pair change that is found within the transmembrane encoding domain of the etr1-1 mutant allele. This chimeric gene was transformed into wild-type Arabidopsis plants. The transformed plants containing the single point mutation that imitated the etr1-1 mutant demonstrated a need for up to an additional five weeks in order to bolt. These mutants also demonstrated dwarf and semidwarf phenotypes with reduced rosette diameters as well as reduced stock heights at maturity. These mutants are similar to the gibberellic acid deficient mutants gai, sly and pkl that are either GA insensitive or have reduced GA biosynthesis (Fridborg et al., 1999). This may indicate that there is cross-talk between the ethylene and GA signal transduction pathways. |
