The Fate ofACCin Higher Plants

Abstract

The fate of 1‐aminocyclopropane‐1‐carboxylate (ACC), generated by the activity of ACC synthase (ACS), is reviewed. In higher plants, ACC undergoes two known fates – the first being malonylation to form malonyl‐ACC (M‐ACC), and the role of this conjugation step as a reversible one to generate free ACC is considered. The second fate is oxidation to form ethylene and HCN. The metabolism of HCN by β‐cyanoalanine synthase (β‐CAS) is considered, including an emerging view of a role for HCN as a signalling compound in plants. For ethylene biosynthesis, the identification of the first candidate gene –pTOM13– with the demonstration of an authentic ethylene‐forming enzyme activity,in vivo, led to a very active research period concerned with the subsequent cloning of ACC oxidase (ACO) genes from a wide variety of plant species and the characterization of the biochemical properties of the enzyme. Together, these studies have contributed to the central conclusion that the ACO gene family is, in most plant species examined, comprised of (usually) 3–5 members that display differential expression in response to developmental and environmental cues. Further, there is growing evidence that ACO (and not ACS) can be the limiting step in terms of ethylene biosynthesis in certain physiological processes. Finally, the evolution of ACO is considered as the key development in the inheritance of the ACC‐dependent ethylene biosynthetic pathway in higher plants.

Ethylene and 1-Aminocyclopropane-1-carboxylate (ACC) in Plant–Bacterial Interactions

“…The plant produced ACC is converted to ET by the action of the enzyme ACO, which is also encoded by a multigene family in higher plants ( Dorling and McManus, 2012 ; Ruduś et al, 2013 ). In Arabidopsis , a total of five ACO genes are found, however only ACO2 and ACO4 have been studied in detail ( Gómez-Lim et al, 1993 ; Raz and Ecker, 1999 ; Ramonell et al, 2002 ; Raghavan et al, 2006 ; Linkies et al, 2009 ).…”

“…These studies revealed that ACO is induced in several plant tissues by numerous treatments, such as, wounding, ethrel (a liquid compound that is transformed into ET), Fe 2+ , 2,4-dichlorophenoxyacetic acid and ACC. Likewise, several studies have demonstrated the induction of ACO gene expression by biotic and abiotic stresses, phytohormone treatments (including ET) and developmental and ontological cues in other plant species (reviewed by Dorling and McManus, 2012 ).…”

“…Like ACS, the ACO enzyme isoforms are expressed under tissue specific conditions and different translational regulation mechanisms control their production ( Dorling and McManus, 2012 ). In addition, ACO expression can also be affected by post-transcriptional and post-translational regulatory mechanisms ( Datta et al, 2015 ).…”

Ethylene-induced transcriptional and hormonal responses at the onset of sugarcane ripening

“…The ethylene biosynthetic pathway is accomplished in mainly two rate-limiting steps coordinated by ACS (converts SAM, S-adenosylmethionine, to ACC) and ACO (converts ACC to ethylene) 43 . Genes encoding both enzymes belong to multigene families, whose transcription exhibit temporal-spatial pattern depending on external and internal stimuli 43 .…”

“…The ethylene biosynthetic pathway is accomplished in mainly two rate-limiting steps coordinated by ACS (converts SAM, S-adenosylmethionine, to ACC) and ACO (converts ACC to ethylene) 43 . Genes encoding both enzymes belong to multigene families, whose transcription exhibit temporal-spatial pattern depending on external and internal stimuli 43 . The transcriptional regulation of ACS and ACO influences ethylene emission 43 , particularly the increase in ACO expression accompanied by protein accumulation or high enzyme activity is a strong indicator of auto-regulation of ethylene production within a tissue 43 44 .…”