Ethylene-Stimulated Nutations Do Not Require ETR1 Receptor Histidine Kinase Activity

Abstract

Ethylene influences the growth and development of plants through the action of receptors that have homology to bacterial two-component receptors. In bacteria these receptors function via autophosphorylation of a His residue in the kinase domain followed by phosphotransfer to a conserved Asp residue in a response regulator protein. In Arabidopsis, two of the five receptor isoforms are capable of His kinase activity. However, the role of His kinase activity and phosphotransfer is unclear in ethylene signaling. A previous study showed that ethylene stimulates nutations of the hypocotyl in etiolated Arabidopsis seedlings that are dependent on the ETR1 receptor isoform. The ETR1 receptor is the only isoform in Arabidopsis that contains both a functional His kinase domain and a receiver domain for phosphotransfer. Therefore, we examined the role that ETR1 His kinase activity and phosphotransfer plays in ethylene-stimulated nutations.

Keywords: ethylene; histidine kinase; nutations; phosphotransfer; receptors; signal transduction; two component signalling.

Figure 1

Ethylene stimulates nutations of etr1-7 seedlings transformed with a kinase-inactivated ETR1 transgene. The hypocotyl angles for four etr1-7 mutants transformed with a kinase-inactivated genomic ETR1 transgene (gETR1(G₂)) are shown. Transformants were obtained from Eric Schaller and have been described previously. In this and the following figure, etiolated Arabidopsis seedlings were imaged from the side at 15 min intervals while growing along a vertically orientated agar plate and the hypocotyl angle measured as described previously. Black and gray lines are used to help distinguish the movements of individual seedlings. All seedlings were grown in the presence of 5 µM AVG to block biosynthesis of ethylene by the seedlings. Seedlings were grown in air for 2 h prior to treatment with 10 µL L⁻¹ ethylene ().

Figure 2

Ethylene stimulates nutations of etr1-6 etr2-3 ein4-4 seedlings transformed with an ETR1 transgene mutated at Asp₆₅₉. The hypocotyl angles from seven etr1-6 etr2-3 ein4-4 triple mutants transformed with an ETR1 transgene mutated at Asp₆₅₉ (getr1[D]) are shown in two panels. One seedling in (A) (black) had no measurable nutations while one in (B) (black) had very small nutations.