Dissecting the role of climacteric ethylene in kiwifruit (Actinidia chinensis) ripening using a 1-aminocyclopropane-1-carboxylic acid oxidase knockdown line

Abstract

During climacteric fruit ripening, autocatalytic (Type II) ethylene production initiates a transcriptional cascade that controls the production of many important fruit quality traits including flavour production and softening. The last step in ethylene biosynthesis is the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene by the enzyme ACC oxidase (ACO). Ten independent kiwifruit (Actinidia chinensis) lines were generated targeting suppression of fruit ripening-related ACO genes and the fruit from one of these lines (TK2) did not produce detectable levels of climacteric ethylene. Ripening behaviour in a population of kiwifruit at harvest is asynchronous, so a short burst of exogenous ethylene was used to synchronize ripening in TK2 and control fruit. Following such a treatment, TK2 and control fruit softened to an 'eating-ripe' firmness. Control fruit produced climacteric ethylene and softened beyond eating-ripe by 5 d. In contrast, TK2 fruit maintained an eating-ripe firmness for >25 d and total volatile production was dramatically reduced. Application of continuous exogenous ethylene to the ripening-arrested TK2 fruit re-initiated fruit softening and typical ripe fruit volatiles were detected. A 17 500 gene microarray identified 401 genes that changed after ethylene treatment, including a polygalacturonase and a pectate lyase involved in cell wall breakdown, and a quinone oxidoreductase potentially involved in volatile production. Many of the gene changes were consistent with the softening and flavour changes observed after ethylene treatment. However, a surprisingly large number of genes of unknown function were also observed, which could account for the unique flavour and textural properties of ripe kiwifruit.

Extension of Shelf-life by Limited Duration of Propylene and 1-MCP Treatments in Three Kiwifruit Cultivars

“…The application of exogenous ethylene or its analogue propylene accelerates the ripening of kiwifruit in four main phases, as hypothesized by Atkinson et al (2011) and Schröder and Atkinson (2006), and as shown in Figure 6. Phase I is the pre-climacteric (unripe) stage characterized by high firmness, high TA, and low SSC, making kiwifruit unsuitable for consumption.…”

“…Atkinson et al (2011) proposed a model of kiwifruit ripening induced by exogenous ethylene (see continuous lines in Fig. 6).…”

Metabolic engineering of aroma components in fruits

“…The microarray expression analysis of a transgenic apple line in which MdACO1 was silenced led to the identification of 17 candidate genes that are likely to be ethylene control points for aroma production in apple [76]. Fruits of this line and fruits of a kiwifruit (Actinidia chinensis) line in which the AcACO1 gene was suppressed [77], presented a phenotype analogous to that described previously in apple [75].…”

Genetics of Fruit Softening

“…also identified nine gene models in the 'Hongyang' predicted coding sequence database for ACC oxidase. The AcACO1/AcACO3 and AcACO4/AcACO6 genes previously identified by Atkinson et al (2011) in 'Hort16A' clustered in pairs, whilst AcACO5 was more distantly related. The additional 'Hongyang' ACO gene models clustered with genes from tomato.…”

“…Suppression of ethylene biosynthetic genes has been a powerful tool in identifying ethylene-controlled traits linked to ripening in tomato, apple, melon and kiwifruit (Oeller et al 1991;Schaffer et al 2007;Pech et al 2008;Atkinson et al 2011). In apple, a model for control of ripening was developed showing that individual ripening characters differ in their sensitivity to ethylene and dependency on ethylene.…”