Recessive and dominant mutations in the ethylene biosynthetic gene ACS 5 of Arabidopsis confer cytokinin insensitivity and ethylene overproduction, respectively

We identified a set of cytokinin-insensitive mutants by using a screen based on the ethylene-mediated triple response observed after treatment with low levels of cytokinins. One group of these mutants disruptsACS5 , a member of theArabidopsis gene family that encodes 1-aminocyclopropane-1-carboxylate synthase, the first enzyme in ethylene biosynthesis. The ACS5 isoform is mainly responsible for the sustained rise in ethylene biosynthesis observed in response to low levels of cytokinin and appears to be regulated primarily by a posttranscriptional mechanism. Furthermore, the dominant ethylene-overproducing mutanteto2 was found to be the result of an alteration of the carboxy terminus ofACS5 , suggesting that this domain acts as a negative regulator of ACS5 function.