The Ethylene Precursor ACC Affects Early Vegetative Development Independently of Ethylene Signaling

Abstract

The plant hormone ethylene plays a pivotal role in virtually every aspect of plant development, including vegetative growth, fruit ripening, senescence, and abscission. Moreover, it acts as a primary defense signal during plant stress. Being a volatile, its immediate biosynthetic precursor, 1-aminocyclopropane-1-carboxylic acid, ACC, is generally employed as a tool to provoke ethylene responses. However, several reports propose a role for ACC in parallel or independently of ethylene signaling. In this study, pharmacological experiments with ethylene biosynthesis and signaling inhibitors, 2-aminoisobutyric acid and 1-methylcyclopropene, as well as mutant analyses demonstrate ACC-specific but ethylene-independent growth responses in both dark- and light-grown Arabidopsis seedlings. Detection of ethylene emanation in ethylene-deficient seedlings by means of laser-based photoacoustic spectroscopy further supports a signaling role for ACC. In view of these results, future studies employing ACC as a proxy for ethylene should consider ethylene-independent effects as well. The use of multiple knockout lines of ethylene biosynthesis genes will aid in the elucidation of the physiological roles of ACC as a signaling molecule in addition to its function as an ethylene precursor.

Ethylene-independent signaling by the ethylene precursor ACC in Arabidopsis ovular pollen tube attraction

“…These findings support the emerging evidence of a signaling function for ACC distinct from its role as the ethylene precursor 3 – 7 . Seed plants typically contain micromolar levels of ACC, allowing for ACC to simultaneously serve both of these functions.…”

“…Responses to ethylene are often assessed by treating plants with ACC, due to the relative ease of application and rapid conversion of ACC to ethylene 2 . However, exceptions to this rule, such as ethylene-independent ACC responses in roots [3][4][5] , guard cells 6 , and reproduction 7 have been reported. In the latter case, an Arabidopsis thaliana octuple mutant of all eight functional ACS genes was generated by expressing an artificial microRNA (amiRNA) that reduced expression of both ACS8 and ACS11 in an acs hextuple knockout mutant background 7 .…”

Ethylene signaling mediates host invasion by parasitic plants

“…Therefore, ACC as a precursor of ethylene might have a different role from ethylene and is required for haustorium formation. In line with this, ethylene signaling-independent function of ACC is known in several processes including pollen tube attraction, seed viability, and vegetative growth, proposing that ACC itself might act as a hormone (31)(32)(33). Alternatively, reduced haustorium initiation may be a consequence of auxin biosynthesis inhibition by AVG.…”

Beyond Ethylene: New Insights Regarding the Role of Alternative Oxidase in the Respiratory Climacteric

“…ACC is subsequently converted into ethylene by 1-aminocyclopropane carboxylate oxidase (ACO). ACC, long known for its role as the immediate precursor to ethylene, has recently been investigated for its potential role in ethyleneindependent regulation of growth (Polko and Kieber, 2019;Vanderstraeten et al, 2019). Following successful perception of ethylene, the hormone signal is transduced via a series of messengers to the nucleus where ethylene-responsive transcription factors (ERFs) activate downstream ripening-associated genes involved in cell wall softening, starch to sugar conversion, aroma production, and changes in pigmentation, among numerous other changes (Seymour et al, 2012;Osorio et al, 2013a;Cherian et al, 2014;Gao et al, 2020).…”