A New Tomato NAC (NAM/ATAF1/2/CUC2) Transcription Factor, SlNAC4, Functions as a Positive Regulator of Fruit Ripening and Carotenoid Accumulation

Abstract

Fruit ripening in tomato (Solanum lycopersicum) is a complicated development process affected by both endogenous hormonal and genetic regulators and external signals. Although the role of NOR, a member of the NAC domain family, in mediating tomato fruit ripening has been established, its underlying molecular mechanisms remain unclear. To explore further the role of NAC transcription factors in fruit ripening, we characterized a new tomato NAC domain protein, named SlNAC4, which shows high accumulation in sepal and at the onset of fruit ripening. Various stress treatments including wounding, NaCl, dehydration and low temperature significantly increased the expression of SlNAC4. Reduced expression of SlNAC4 by RNA interference (RNAi) in tomato resulted in delayed fruit ripening, suppressed Chl breakdown and decreased ethylene synthesis mediated mainly through reduced expression of ethylene biosynthesis genes of system-2, and reduced carotenoids by alteration of the carotenoid pathway flux. Transgenic tomato fruits also displayed significant down-regulation of multiple ripening-associated genes, indicating that SlNAC4 functions as a positive regulator of fruit ripening by affecting ethylene synthesis and carotenoid accumulation. Moreover, we also noted that SlNAC4 could not be induced by ethylene and may function upstream of the ripening regulator RIN and positively regulate its expression. Yeast two-hybrid assay further revealed that SlNAC4 could interact with both RIN and NOR protein. These results suggested that ethylene-dependent and -independent processes are regulated by SlNAC4 in the fruit ripening regulatory network.

Natural Variation in Monoterpene Synthesis in Kiwifruit: Transcriptional Regulation of Terpene Synthases by NAC and ETHYLENE-INSENSITIVE3-Like Transcription Factors

“…It is conceivable that, prior to fruit ripening, other flavor-related gene promoters and promoters involved in ethylene biosynthesis and softening are actively repressed. Such complexity has been observed in tomato, where the action of the APETALA2 (AP2) class TF SlAP2a/AP2a (Chung et al, 2010;Karlova et al, 2011) negatively regulates fruit ripening, whereas the action of positive signals such as LeMADS-RIN (Vrebalov et al, 2002), CLEAR NON-RIPENING/Cnr (Manning et al, 2006), TAGL1 (Vrebalov et al, 2009), LeHB-1 , and the NAC TFs SlNAC4 and NOR (Martel et al, 2011;Zhu et al, 2014) promotes ripening.…”

“…The rin mutation has been shown to be encoded by a MADS-box TF (Vrebalov et al, 2002) and Cnr by a SQUAMOSA promoter-binding protein (Manning et al, 2006). An uncharacterized NAC (for no apical meristem [NAM], Arabidopsis transcription activation factor [ATAF], and cup-shaped cotyledon [CUC]-domain transcription factor)-domain TF mutation leads to the nor mutant phenotype (Martel et al, 2011), while SlNAC4 could interact with NOR and RIN proteins to affect fruit ripening and carotenoid accumulation (Zhu et al, 2014). Other tomato TFs shown to influence volatile production in fruit include the tomato homeobox protein (LeHB-1; Lin et al, 2008), which induces LeACO1 and ethylene production, and the MADS-box protein TOMATO AGAMOUS-LIKE1 (TAGL1; Itkin et al, 2009;Vrebalov et al, 2009) through direct activation of LeACS2.…”

Identification of candidate genes associated with mealiness and maturity date in peach [Prunus persica (L.) Batsch] using QTL analysis and deep sequencing

“…Pons et al (2014) proposed that another TF (TT19) is related to the accumulation of anthocyanin and proanthocyanin, and is involved in cell wall composition and sensitivity to chilling. The genes ppa020620m, ppa025596m, and ppa008301m encoding for NAC TFs are specific to plants and are involved in MD Romeu et al 2014), ripening (Giovannoni et al 1995;Thompson et al 1999;Giovannoni 2007;Shan et al 2012;Zhu et al 2014), biotic and abiotic stress (Fujita et al 2004;He et al 2005;Nakashima et al 2007;Hu et al 2008;Nakashima et al 2012;Jin et al 2013). Furthermore, these TFs are involved in the ABA-dependent response to dehydration, reactive oxygen species detoxification and defense (Fujita et al 2004).…”

Ripening of Tomato Fruit and Susceptibility to Botrytis cinerea

“…The susceptibility of fruit with altered expression of the negative ripening regulators: SlMADS1, a tomato homolog of APETALLA SlAP2a and the ethylene response factor SlERF6 (Chung et al 2010 ;Karlova et al 2011Karlova et al , 2013Lee et al 2012 ;Dong et al 2013 ), or the positive regulators, SlNAC4, TOMATO AGAMOUS-LIKE 1 (SlTAGL1), the tomato FRUITFULL homologs (SlFUL1 and SlFUL2) and the HD-Zip homeobox transcription factor SlHB1 (Lin et al 2008 ;Shima et al 2013 ;Zhu et al 2014 ;Fujisawa et al 2014 ) has not been evaluated. Other transcription regulators related to fruit development, but not directly involved in ripening, could also impact the outcome of fruit-B.…”