Two Arabidopsis Mutants That Overproduce Ethylene Are Affected in the Posttranscriptional Regulation of 1-Aminocyclopropane-1-Carboxylic Acid Synthase1

Abstract

The Arabidopsis mutants eto1 (ethylene overproducer) and eto3 produce elevated levels of ethylene as etiolated seedlings. Ethylene production in these seedlings peaks at 60 to 96 h, and then declines back to almost wild-type levels. Ethylene overproduction in eto1 and eto3 is limited mainly to etiolated seedlings; light-grown seedlings and various adult tissues produce close to wild-type amounts of ethylene. Several compounds that induce ethylene biosynthesis in wild-type, etiolated seedlings through distinct 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) isoforms were found to act synergistically with eto1 and eto3, as did the ethylene-insensitive mutation etr1 (ethylene resistant), which blocks feedback inhibition of biosynthesis. ACS activity, the rate-limiting step of ethylene biosynthesis, was highly elevated in both eto1 and eto3 mutant seedlings, even though RNA gel-blot analysis demonstrated that the steady-state level of ACS mRNA was not increased, including that of a novel Arabidopsis ACS gene that was identified. Measurements of the conversion of ACC to ethylene by intact seedlings indicated that the mutations did not affect conjugation of ACC or the activity of ACC oxidase, the final step of ethylene biosynthesis. Taken together, these data suggest that the eto1 and eto3 mutations elevate ethylene biosynthesis by affecting the posttranscriptional regulation of ACS.

The eto1, eto2, and eto3 Mutations and Cytokinin Treatment Increase Ethylene Biosynthesis in Arabidopsis by Increasing the Stability of ACS Protein

“…The eto2 mutation does not increase the steady state level of ACS5 mRNA, which suggests that the mutation acts post-transcriptionally (Vogel et al, 1998). Furthermore, in both eto1 and eto3 , the steady state levels of all of the ACS transcripts examined were not significantly higher than those observed in wild-type seedlings, although the level of ACS activity from eto1 and eto3 etiolated seedlings was highly increased (Woeste et al, 1999). These results suggest that these mutants also are affected in the posttranscriptional regulation of ACS.…”

“…Previous studies of the ethylene-overproducing mutants eto1 and eto3 suggested that these mutations affect the post-transcriptional regulation of ACS (Woeste et al, 1999). To learn more about the mechanism by which ACS is regulated at the post-transcriptional level, the ETO3 gene was cloned using a map-based approach.…”

Mutation ofE1-CONJUGATING ENZYME-RELATED1Decreases RELATED TO UBIQUITIN Conjugation and Alters Auxin Response and Development

“…Intriguingly, CUL3 can be RUB modified (Figueroa et al, 2005) and is a component of a ubiquitin-protein ligase that can include ETO1, which targets ACS5 for ubiquitin-dependent degradation (Wang et al, 2004). ACS enzyme activity (Woeste et al, 1999) and ACS5 protein levels (Wang et al, 2004) are enhanced in eto1 mutants, and it will be interesting to learn whether ACS5 is similarly stabilized in ecr1, rce1, or rub mutants. It remains mysterious why axr1 displays opposite ethylene phenotypes, ethylene resistance (Timpte et al, 1995) and less ethylene production than wild type (Bostick et al, 2004), compared to other RUB pathway mutants.…”

Multifunctional acetyl‐CoA carboxylase 1 is essential for very long chain fatty acid elongation and embryo development in Arabidopsis

“…Ethylene biosynthesis is reported to be downregulated through 1-aminocyclopropane-1-carboxylate malonylation (Guo et al, 1993). This pathway does not seem to interfere with embryo development, since ethylene overproducer mutants exhibit normal embryo development (Woeste et al, 1999). Waxes that contain VLCFA are deposited once embryo morphogenesis is achieved and therefore are unlikely to be involved.…”