SlNAP1 promotes tomato fruit ripening by regulating carbohydrate metabolism.

Many studies showed NAC transcription factors play an important role in fruit ripening. Moreover, sucrose and starch metabolism is also closely related to fruit ripening. However, there are a few studies focus on whether NAC regulates sucrose and starch metabolism to influence fruit ripening. In this study, virus-induced gene silencing (VIGS) of SlNAP1 suppressed fruit ripening and delayed color transformation. The chlorophyll (including Chla, Chlb, and Chla + b) degradation and carotenoid synthesis in SlNAP1-silenced fruits were dramatically suppressed. Silencing SlNAP1 decreased soluble sugar and reducing sugar accumulation in fruits, and increased starch content. The activity of starch degrading enzymes, including α amylase (AMY) and β amylase (BAM) was significantly lower in SlNAP1-silenced fruits than in the control fruits, whereas denosine diphosphoglucose pyrophosphorylase (AGP) activity was significantly higher. In addition, the expression of starch degradation-related genes (SlAMY1, SlAMY2, SlBAM1, SlBAM7, SlGWD, SlPWD) in SlNAP1-silenced fruits was significantly suppressed, while starch synthesis-related genes (SlAGPase1, SlAGPase2) was significantly increased. Compared with the control fruits, SlNAP1-silenced fruits showed significantly lower sucrose and glucose content. The expression level of sucrose and glucose metabolism-related genes such as Slsus1, Slsus3, SlSPS, SlHxk1, SlHxk2, SlPK1, and SlPK2 was significantly lower in SlNAP1-silenced fruits than in the control fruits. Overall, this study revealed that SlNAP1 gene might positively regulate fruit ripening by influencing carbohydrate metabolism.
Competing Interests: Declaration of competing interest The authors declare no conflict of interest.
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