Abstract
Cell wall catabolism during fruit ripening is under complex control and is key for fruit quality and shelf life. To examine the role of abscisic acid (ABA) in tomato (Solanum lycopersicum) fruit ripening, we suppressed SlNCED1, which encodes 9-cis-epoxycarotenoid dioxygenase (NCED), a key enzyme in the biosynthesis of ABA. To suppress SlNCED1 specifically in tomato fruits, and thus avoid the pleiotropic phenotypes associated with ABA deficiency, we used an RNA interference construct driven by the fruit-specific E8 promoter. ABA accumulation and SlNCED1 transcript levels in the transgenic fruit were down-regulated to between 20% and 50% of the levels measured in the control fruit. This significant reduction in NCED activity led to a down-regulation in the transcription of genes encoding major cell wall catabolic enzymes, specifically polygalacturonase (SlPG), pectin methyl esterase (SlPME), β-galactosidase precursor mRNA (SlTBG), xyloglucan endotransglycosylase (SlXET), endo-1,4-β-cellulose (SlCels), and expansin (SlExp). This resulted in an increased accumulation of pectin during ripening. In turn, this led to a significant extension of the shelf life to 15 to 29 d compared with a shelf life of only 7 d for the control fruit and an enhancement of fruit firmness at the mature stage by 30% to 45%. In conclusion, ABA affects cell wall catabolism during tomato fruit ripening via down-regulation of the expression of major catabolic genes (SlPG, SlPME, SlTBG, SlXET, SlCels, and SlExp).
Highlights
The plant hormone abscisic acid (ABA) regulates seed dormancy, plant growth and responses to environmental stresses (Leung and Giraudat, 1998; Nambara and Marion-Poll, 2003; Finkelstein, 2006; Shinozaki and Yamaguchi-Shinozaki, 2007), but it regulates fruit ripening (Kondo et al, 2002; Jiang and Joyce, 2003; Giovannoni, 2007; Galpaz et al, 2008)
We examined the expression levels of genes involved in ABA synthesis (SlNCED1/2) and ABA catabolism (SlCYP707A1/2/3)
The results of this study show that SlNCED1-RNAi driven by E8 effectively reduces the transcription of SlNCED1 and the accumulation of ABA in fruit, which affects several metabolic pathways of fruit ripening in a pleiotropic manner
Summary
The plant hormone abscisic acid (ABA) regulates seed dormancy, plant growth and responses to environmental stresses (Leung and Giraudat, 1998; Nambara and Marion-Poll, 2003; Finkelstein, 2006; Shinozaki and Yamaguchi-Shinozaki, 2007), but it regulates fruit ripening (Kondo et al, 2002; Jiang and Joyce, 2003; Giovannoni, 2007; Galpaz et al, 2008). –allenic-apo-aldehyde in which reactions are catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED) (Tan et al, 1997; Burbidge et al, 1999; Qin and Zeevaart, 1999; Iuchi et al, 2001; Rodrigo et al, 2006). Since it was first isolated from the maize vp[14] mutant (Tan et al, 1997), NCED has been cloned and characterized in various plant species (Iuchi et al, 2000; Rodrigo et al 2003; Wheeler et al, 2009). Active ABA is either degraded to inactive compounds through an irreversible pathway starting with 8' hydroxylation and catalyzed by ABA 8'-hydroxylase (CYP707As), or is stored in bound form as ABA-glucosylester, formation of which is catalyzed by ABA glucosyltransferase (Zeevaart et al, 1998, 1999; Barthe et al, 2000). Studies of ABA receptor proteins (Shen et al, 2006; Pandey et al, 2009; Muller and Hansson, 2009; Wu et al, 2009) and ABA signaling have defined the ABA signal transduction pathway (Ma et al, 2009; Melcher et al, 2009; Nishimura et al, 2009; Park et al, 2009), which includes three core components: the ABA receptors
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