Abstract
Ethylene influences many aspects of plant growth and development. The biosynthesis of ethylene is highly regulated by a variety of internal and external cues. A key target of this regulation is 1-aminocyclopropane-1-carboxylic acid (ACC) synthases (ACS), generally the rate-limiting step in ethylene biosynthesis, which is regulated both transcriptionally and post-transcriptionally. Prior studies have demonstrated that cytokinin and brassinosteroid (BR) act as regulatory inputs to elevate ethylene biosynthesis by increasing the stability of ACS proteins. Here, we demonstrate that several additional phytohormones also regulate ACS protein turnover. Abscisic acid, auxin, gibberellic acid, methyl jasmonic acid, and salicylic acid differentially regulate the stability of ACS proteins, with distinct effects on various isoforms. In addition, we demonstrate that heterodimerization influences the stability of ACS proteins. Heterodimerization between ACS isoforms from distinct subclades results in increased stability of the shorter-lived partner. Together, our study provides a comprehensive understanding of the roles of various phytohormones on ACS protein stability, which brings new insights into crosstalk between ethylene and other phytohormones, and a novel regulatory mechanism that controls ACS protein stability through a heterodimerization of ACS isoforms.
Highlights
The gaseous hormone ethylene influences a wide range of plant growth and development processes as well as stress responses, which are in part conferred by crosstalk with other phytohormones (Abeles et al, 1992, Vanstraelen and Benkova, 2012, Van de Poel et al, 2015) .Ethylene is derived from the amino acid methionine and converted to ethylene via two intermediates, S-adenyl methionine (AdoMet) and 1-aminocyclopropane-1-carboxylic acid (ACC) (Yang and Hoffman, 1984)
Auxin, gibberellic acid, methyl jasmonic acid, and salicylic acid differentially regulate the stability of ACC synthases (ACS) proteins, with distinct effects on various isoforms
Our study provides a comprehensive understanding of the roles of various phytohormones on ACS protein stability, which brings new insights into crosstalk between ethylene and other phytohormones, and a novel regulatory mechanism that controls ACS protein stability through a heterodimerization of ACS isoforms
Summary
Ethylene is derived from the amino acid methionine and converted to ethylene via two intermediates, S-adenyl methionine (AdoMet) and 1-aminocyclopropane-1-carboxylic acid (ACC) (Yang and Hoffman, 1984). S-adenyl methionine synthase (AdoMet synthase) converts methionine to AdoMet, which is subsequently converted to ACC by ACC synthases (ACS). Ethylene is made from ACC by ACC oxidases, a member of the oxygenase/oxidase superfamily of enzymes (John, 1991, Bidonde et al, 1998, Ryle and Hausinger, 2002). The conversion of AdoMet to ACC is generally the rate-limiting step of the pathway and is catalyzed by a family of ACS enzymes. Type-2 ACS proteins contain the Target of ETO1 (TOE) domain that serves as a binding site for the E3 ligases, Ethylene Overproducer 1
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