Fruit-specific RNAi-mediated suppression of SlNCED1 increases both lycopene and β-carotene contents in tomato fruit

Abstract

Abscisic acid (ABA) plays important roles during tomato fruit ripening. To study the regulation of carotenoid biosynthesis by ABA, the SlNCED1 gene encoding 9-cis-epoxycarotenoid dioxygenase (NCED), a key enzyme in the ABA biosynthesis, was suppressed in tomato plants by transformation with an RNA interference (RNAi) construct driven by a fruit-specific E8 promoter. ABA accumulation and SlNCED1 transcript levels in the transgenic fruit were down-regulated to between 20–50% of that in control fruit. This significant reduction in NCED activity led to the carbon that normally channels to free ABA as well as the ABA metabolite accumulation during ripening to be partially blocked. Therefore, this ‘backlogged’ carbon transformed into the carotenoid pathway in the RNAi lines resulted in increased assimilation and accumulation of upstream compounds in the pathway, chiefly lycopene and β-carotene. Fruit of all RNAi lines displayed deep red coloration compared with the pink colour of control fruit. The decrease in endogenous ABA in these transgenics resulted in an increase in ethylene, by increasing the transcription of genes related to the synthesis of ethylene during ripening. In conclusion, ABA potentially regulated the degree of pigmentation and carotenoid composition during ripening and could control, at least in part, ethylene production and action in climacteric tomato fruit.

Ethylene control of fruit ripening: revisiting the complex network of transcriptional regulation

“…The expression of ACS2, ACS4, and ACO1 genes is induced by exogenous ABA, revealing an ABA/ ethylene interplay operating at the level of ethylene biosynthesis (Chernys and Zeevaart, 2000;Jiang et al, 2000;Zhang et al, 2009). Down-regulation of the key ABA biosynthesis enzyme 9-cis-epoxycarotenoid dioxygenase1 in tomato fruit resulted in altered firmness and color but surprisingly higher ethylene production, indicating the complexity of the ABA/ethylene interplay during ripening (Sun et al, 2012). In tomato, ABA might also be perceived through an ethylene-independent pathway that is mediated by tomato Zinc Finger Transcription Factor (Weng et al, 2015).…”

The Zinc Finger Transcription Factor SlZFP2 Negatively Regulates Abscisic Acid Biosynthesis and Fruit Ripening in Tomato

“…Besides ethylene and the abovementioned regulators, ABA also is implicated to play a role in the fruit ripening of tomato and other species, including nonclimacteric fruit crops such as strawberry (Fragaria ananassa) and grape (Vitis vinifera; Jia et al, 2011;Seymour et al, 2013), although the mechanism remains unclear. In tomato, repression of LeNCED1 decreases the expression of several genes encoding ripening-associated cell wall enzymes and delays fruit ripening, suggesting that ABA promotes ripening (Sun et al, 2012b).…”

ABA-deficiency and molecular mechanisms involved in the dehydration response and ripening of citrus fruit

“…Clade A PP2Cs function as negative regulators of the ABA signalling pathway and their transcript levels are highly induced by ABA in plants (Merlot et al, 2001;Saez et al, 2004;Saez et al, 2006;Yoshida et al, 2006b;Xue et al, 2008;Li et al, 2009) Fig.1 and 4A, Results Chapter 1), which agreed with results reported in harvested grapes and tomatoes (Sun et al, 2010;Sun et al, 2012a;Sun et al, 2012b) and in vegetative tissues (Tan et al, 2003;Loyola et al, 2012;Frey et al, 2012). Interestingly, CsNCED1 followed an expression pattern highly similar to that displayed by the members of the CsPP2CA family in citrus fruit (Fig.2, Results Chapter 3).…”

“…Studies performed in tomato, avocado, peach and persimmon indicated that NCED genes expression was induced as ripening progressed, showing a maximum before the ethylene production (Chernys and Zeevaart, 2000;Leng et al, 2009;Zhang et al, 2009a;Sun et al, 2012b). In nonclimacteric fruits such as strawberry, watermelon, sweet cherry and grape, NCED genes were mainly induced in response to water stress and ABA application, and transcripts accumulation paralleled ABA increase during fruit ripening (Zhang et al, 2009a;Ren et al, 2010;Ji et al, 2012;Li et al, 2012b).…”