Single site mutant protein turnover6/22/2023 In the first step, methionine is converted to SAM by SAM synthases. Ethylene is synthesized from the amino acid methionine via two intermediates, S-adenosyl methionine (SAM) and 1-aminocyclopropane-1-carboxylic acid (ACC) ( Adams and Yang, 1977 Lieberman and Mapson, 1964). The pathway of ethylene biosynthesis is simple and straightforward. 1) ( Kende, 1993 Yang and Hoffman, 1984 Zarembinski and Theologis, 1994). Through the efforts of Yang and co-workers, the biosynthesis of ethylene was fully elucidated in late 1980’s ( Fig. 30 years later, Gane showed that ethylene is naturally produced by plants ( Gane, 1934). This seedling phenotype was later defined as the triple response, which is a hallmark of the ethylene response of dark-grown seedlings ( Knight et al., 1910). The pea seedlings exhibited distinctive morphology changes which include shortening of hypocotyl and root, swelling and thickening of hypocotyl, and formation of exaggerated hook. Neljubov used pea seedlings to determine that ethylene is the active component of the illuminating gas by exposing the filtered illuminating gas to pea seedlings. The Russian scientist Neljubov first demonstrated that ethylene is the responsible component caused the early defoliation of the tree nearby a leaking illuminating gas main in a small German town in the late1800’s ( Neljubov, 1901). Ethylene influences many aspects of plant growth and developmental processes, including germination, fruit ripening, flower senescence, leaf abscission, nodulation, lateral root initiation, and the response to a variety of abiotic and biotic stresses ( Abeles et al., 1992 Mattoo and Suttle, 1991). The simple gas ethylene has been recognized as a plant growth regulator for a century ( Crocker and Knight, 1908 Knight et al., 1910 Neljubov, 1901). The prospect of cross-talk between ethylene biosynthesis and other signaling pathways to control turnover of the ACS protein is also considered. In this review, recent new insight into the regulation of ACS protein turnover is highlighted, with a special focus on the roles of phosphorylation, ubiquitination, and novel components that regulate the turnover of ACS proteins. Together with molecular genetic studies suggesting the roles of post-translational modification of the ACS, newly emerging evidence strongly suggests that the regulation of ACS protein stability is an alternative mechanism that controls ethylene production, in addition to the transcriptional regulation of ACS genes. The enzyme 1-aminocyclopropane-1-carboxylic acid synthase (ACS), which catalyzes the rate-limiting step of ethylene biosynthesis, plays a central role to regulate ethylene production through changes in ACS gene expression levels and the activity of the enzyme. Biosynthesis of the phytohormone ethylene is under tight regulation to satisfy the need for appropriate levels of ethylene in plants in response to exogenous and endogenous stimuli.
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