title: Ethylene regulates Apple (Malus x domestica) fruit softening through a dose x time-dependent mechanism and through differential sensitivities and dependencies of cell wall-modifying genes.
abstract: In fleshy fruit species that have a strong requirement for ethylene to ripen, ethylene is synthesized autocatalytically, producing increasing concentrations as the fruits ripen. Apple fruit with the ACC OXIDASE 1 (ACO1) gene suppressed cannot produce ethylene autocatalytically at ripening. Using these apple lines, an ethylene sensitivity dependency model was previously proposed, with traits such as softening showing a high dependency for ethylene as well as low sensitivity. In this study, it is shown that the molecular control of fruit softening is a complex process, with different cell wall-related genes being independently regulated and exhibiting differential sensitivities to and dependencies on ethylene at the transcriptional level. This regulation is controlled through a dose × time mechanism, which results in a temporal transcriptional response that would allow for progressive cell wall disassembly and thus softening. This research builds on the sensitivity dependency model and shows that ethylene-dependent traits can progress over time to the same degree with lower levels of ethylene. This suggests that a developmental clock measuring cumulative ethylene controls the fruit ripening process.
authors.affiliation: The New Zealand Institute for Plant & Food Research Ltd, Private Bag 92169, Auckland 1142, New Zealand.
authors.forename: Hilary S
authors.initials: HS
authors.lastname: Ireland
authors.forename: Kularajathevan
authors.initials: K
authors.lastname: Gunaseelan
authors.forename: Ratnasiri
authors.initials: R
authors.lastname: Muddumage
authors.forename: Emma J
authors.initials: EJ
authors.lastname: Tacken
authors.forename: Jo
authors.initials: J
authors.lastname: Putterill
authors.forename: Jason W
authors.initials: JW
authors.lastname: Johnston
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Schaffer
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D002473:Cell Wall / Q000235:genetics* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005030:Ethylenes / Q000494:pharmacology*; D005638:Fruit / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D027845:Malus / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D010937:Plant Growth Regulators / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors
chemical_list: D005030:Ethylenes; D010937:Plant Growth Regulators; D010940:Plant Proteins; D011956:Receptors, Cell Surface; C083750:ethylene receptors, plant; D000594:Amino Acid Oxidoreductases; C059460:1-aminocyclopropane-1-carboxylic acid oxidase
keywords: Cell wall; Cumulative ethylene; Malus; Ripening; Softening