Mutational loss of the prohibitin AtPHB3 results in an extreme constitutive ethylene response phenotype coupled with partial loss of ethylene-inducible gene expression in Arabidopsis seedlings.

The eer3-1 loss-of-function mutant, which was identified by screening for Arabidopsis mutant seedlings with an enhanced ethylene response, has both increased sensitivity and profound exaggeration of response to ethylene when visually assessed, yet exhibits partial ethylene insensitivity at the molecular level. The eer3-1 mutation represents a conditional allele with an ethylene-dependent phenotype that results from an amino acid substitution in the previously uncharacterized prohibitin, AtPHB3, with complete loss of EER3 function resulting in an extreme constitutive ethylene response in air. Prohibitins in other organisms have diverse roles including transcriptional regulation, with loss of prohibitin function in this capacity associated with tumour formation in mammals. Subcellular localization of AtPHB3 indicates that it is found in several cellular locations, including the nucleus and throughout the cytoplasm. Genetic analysis demonstrates that EER3 functions downstream of EIN2, since an ein2-5;eer3-2 double mutant has the same profound hypocotyl inhibition phenotype seen with the eer3-2 mutant. Based on the presented work, AtPHB3 probably functions as a positive regulator of expression of a subset of ethylene-regulated genes along with a group of genes required to maintain growth in the presence of ethylene.

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