Characterization of two ethylene receptors PhERS1 and PhETR2 from petunia: PhETR2 regulates timing of anther dehiscence.

Two cDNAs (PhERS1 and PhETR2) encoding ethylene receptor homologues were cloned and characterized from petunia. Genomic Southern blot analysis revealed that small families of PhERS1-related and PhETR2-related genes exist in petunia. PhERS1 and PhETR2 are constitutively expressed in stem, flower bud, flower, and roots, with a very low level in leaves. High levels of both PhERS1 and PhETR2 transcripts were detectable in petunia leaves treated with exogenous ethylene, while only PhETR2 mRNA increased after wounding and salt treatment. Arabidopsis plants transformed with a site-mutated PhERS1 in the potential ethylene-binding domain exhibited partial ethylene insensitivity, suggesting that the function of this domain is conserved in the two species. Transgenic petunia plants with decreased PhERS1 expression caused by double-stranded RNA inhibition (dsRNAi) exhibited the wild-type phenotype, but showed increased mRNA levels of PhETR2. This suggests functional compensation between the two genes. Antisense suppression of PhETR2 in petunia led to stomium degeneration and anther dehiscence before anthesis, indicating that PhETR2 regulates synchronization of anther dehiscence with flower opening. Tandem affinity purification (TAP)-tagged PhERS1 was transiently expressed in Nicotiana benthamiana leaves. Gel filtration analysis showed that TAP-PhERS1 forms an approximately 300 kDa protein complex in vivo.