The Role of Ethylene and Cold Temperature in the Regulation of the Apple POLYGALACTURONASE1 Gene and Fruit Softening    

Abstract

Fruit softening in apple (Malus 3 domestica) is associated with an increase in the ripening hormone ethylene. Here, we show that in cv Royal Gala apples that have the ethylene biosynthetic gene ACC OXIDASE1 suppressed, a cold treatment preconditions the apples to soften independently of added ethylene. When a cold treatment is followed by an ethylene treatment, a more rapid softening occurs than in apples that have not had a cold treatment. Apple fruit softening has been associated with the increase in the expression of cell wall hydrolase genes. One such gene, POLYGALACTURONASE1 (PG1), increases in expression both with ethylene and following a cold treatment. Transcriptional regulation of PG1 through the ethylene pathway is likely to be through an ETHYLENE-INSENSITIVE3-like transcription factor, which increases in expression during apple fruit development and transactivates the PG1 promoter in transient assays in the presence of ethylene. A coldrelated gene that resembles a COLD BINDING FACTOR (CBF) class of gene also transactivates the PG1 promoter. The transactivation by the CBF-like gene is greatly enhanced by the addition of exogenous ethylene. These observations give a possible molecular mechanism for the cold-and ethylene-regulated control of fruit softening and suggest that either these two pathways act independently and synergistically with each other or cold enhances the ethylene response such that background levels of ethylene in the ethylene-suppressed apples is sufficient to induce fruit softening in apples.

Influence of 1-Methylcyclopropene Treatment on Postharvest Quality of Four Scab (Venturia inaequalis)-Resistant Apple Cultivars

“…Firmness of most fruits is associated mainly with changes in pectin composition, especially galacturonic acid. Activities of enzymes involved in pectin degradation and fruit softening are generally ethylenedependent [20,21]. There is an agreement that 1-MCP treatment maintains fruit firmness through inhibition of ethylene action and reducing activities of cell wall hydrolases [22].…”

Changes in gene expression profile during fruit development determine fruit quality

“…Moreover, softening of apples is also regulated by the increase in expression of number of cell wall degradation-related genes such as polygalacturonase PG, for which the induction during fruits maturation occurred in cvs McIntosh and Golden Delicious. The facts above point out the positive regulation of fruit softening and negative regulation of fruit firmness processes con- 43, 2016 (1): 1-9 firmed by other authors (Percy et al 1996;Park et al 2006;Payasi et al 2009;Tacken et al 2010). An important group of genes playing a key role in fruit formation and growth are genes regulating cells division processes.…”

“…Recently, many reports have been released with regard to ethylene regulation in plants and fruit softening (Goulao, Oliveira, 2007;Janssen et al 2008;Han et al 2008;Costa et al 2010;Tacken et al 2010;Ireland et al 2013). Our study focused on the genes coding major ACC and ethylene system 1 receptors (Peth and ETR), revealed by Janssen et al (2008).…”

“…Depending on the initiation of ethylene production pathways, fruits are categorized as climacteric and non-climacteric (Lelievre et al 1997;Giovannoni 2004;Seo, Taek 2009;Tacken et al 2010). The primary components of controlling the rate of ethylene production in climacteric fruits are 1-aminocyclopropane-1-carboxylic oxidase (ACO) and 1-aminocyclopropane-1-carboxylic synthase (ACS), which activate ethylene system 1 (Lelievre et al 1997;Barry et al 2000;Shi et al 2013).…”

A 3-D Model of a Perennial Ryegrass Primary Cell Wall and Its Enzymatic Degradation

“…The capacity to simulate enzymatic action could be used to explore modification of PCWs by endogenous enzymes. An important potential application in this context is ripening of fruit, which involves a range of enzymes [75] including the pectin-degrading polygalacturonase [76,77] and could be invaluably explored in the context of an in silico model. The 3-D representation of a primary perennial ryegrass cell wall provided by the model can be sequentially manipulated and modified, and provides an opportunity to explore different models of primary and secondary cell-wall architecture and hypotheses of how cell-wall components are linked.…”