Abstract Background In Arabidopsis , ETO1 (ETHYLENE-OVERPRODUCER1) is a negative regulator of ethylene evolution by interacting with AtACS5, an isoform of the rate-limiting enzyme, 1-aminocyclopropane-1-carboxylate synthases (ACC synthase or ACS), in ethylene biosynthetic pathway. ETO1 directly inhibits the enzymatic activity of AtACS5. In addition, a specific interaction between ETO1 and AtCUL3, a constituent of a new type of E3 ubiquitin ligase complex, suggests the molecular mechanism in promoting AtACS5 degradation by the proteasome-dependent pathway. Because orthologous sequences to ETO1 are found in many plant species including tomato, we transformed tomato with Arabidopsis ETO1 to evaluate its ability to suppress ethylene production in tomato fruits. Results Transgenic tomato lines that overexpress Arabidopsis ETO1 ( ETO1 -OE) did not show a significant delay of fruit ripening. So, we performed yeast two-hybrid assays to investigate potential heterologous interaction between ETO1 and three isozymes of ACC synthases from tomato. In the yeast two-hybrid system, ETO1 interacts with LE-ACS3 as well as AtACS5 but not with LE-ACS2 or LE-ACS4, two major isozymes whose gene expression is induced markedly in ripening fruits. According to the classification of ACC synthases, which is based on the C-terminal amino acid sequences, both LE-ACS3 and AtACS5 are categorized as type 2 isozymes and possess a consensus C-terminal sequence. In contrast, LE-ACS2 and LE-ACS4 are type 1 and type 3 isozymes, respectively, both of which do not possess this specific C-terminal sequence. Yeast two-hybrid analysis using chimeric constructs between LE-ACS2 and LE-ACS3 revealed that the type-2-ACS-specific C-terminal tail is required for interaction with ETO1. When treated with auxin to induce LE-ACS3 , seedlings of ETO1 -OE produced less ethylene than the wild type, despite comparable expression of the LE-ACS3 gene in the wild type. Conclusion These results suggest that ETO1 family proteins specifically interact with and negatively regulate type 2 ACC synthases. Our data also show that Arabidopsis ETO1 can regulate type 2 ACS in a heterologous plant, tomato.
Despite its simple two-carbon structure, the olefin ethylene is a potent modulator of plant growth and development ([Ecker, 1995][1]). The plant hormone ethylene is involved in many aspects of the plant life cycle, including seed germination, root hair development, root nodulation, flower senescence
Reb1p is a DNA binding protein of Saccharomyces cerevisiae that has been implicated in the activation of transcription by polymerase (Pol) II, in the termination of transcription by Pol I, and in the organization of nucleosomes. Studies of the transcriptional control of the REB1 gene have led us to identify three Reb1p binding sites in the 5′ region of the its gene, termed A, B, and C, at positions −110, −80, and +30 with respect to transcription initiation. In vitro, Reb1p binds to the three sites with the relative affinity of A ≥ C > B. Kinetic parameters suggest that when both A and C sites are present on the same DNA molecule, the C site may recruit Reb1p for the A site. In vivo the A and B sites each contribute to the transcription activity ofREB1 in roughly additive fashion. Mutation of both A and B sites abolishes transcription. On the other hand, the C site is a negative element, reducing transcription by 40%. In cells overexpressing Reb1p, the C site reduces transcription by more than 80%. This effect can be transposed to another transcription unit, demonstrating that the effect of Reb1p binding at the C site does not depend on interaction with upstream Reb1p molecules. Relocation of the C site to a position 105 bp downstream of the transcription initiation site abolishes its effect, suggesting that it does not act as a conventional attenuator of transcription. We conclude that binding of Reb1p at the C site hinders formation of the initiation complex. This arrangement of Reb1p binding sites provides a positive and negative mechanism to autoregulate the expression of REB1. Such an arrangement could serve to dampen the inevitable fluctuation in Rep1p levels caused by the intermittent presence of its mRNA within an individual cell.
The rate and plane of cell division and anisotropic cell growth are critical for plant development and are regulated by diverse mechanisms involving several hormone signaling pathways.Little is known about peptide signaling in plant growth; however, Arabidopsis thaliana POLARIS (PLS), encoding a 36-amino acid peptide, is required for correct root growth and vascular development.Mutational analysis implicates a role for the peptide in hormone responses, but the basis of PLS action is obscure.Using the Arabidopsis root as a model to study PLS action in plant development, we discovered a link between PLS, ethylene signaling, auxin homeostasis, and microtubule cytoskeleton dynamics.Mutation of PLS results in an enhanced ethylene-response phenotype, defective auxin transport and homeostasis, and altered microtubule sensitivity to inhibitors.These defects, along with the short-root phenotype, are suppressed by genetic and pharmacological inhibition of ethylene action.PLS expression is repressed by ethylene and induced by auxin.Our results suggest a mechanism whereby PLS negatively regulates ethylene responses to modulate cell division and expansion via downstream effects on microtubule cytoskeleton dynamics and auxin signaling, thereby influencing root growth and lateral root development.This mechanism involves a regulatory loop of auxin-ethylene interactions.
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