Sucrose Promotes Strawberry Fruit Ripening and Affects Ripening-Related Processes

Abstract

Strawberry is a typical nonclimacteric fruit, whose ripening mechanism needs to be further investigated. Sucrose has been recently proved as a signal molecule, participating in strawberry fruit ripening and related processes. While in the effects of sucrose application timing and concentration on ripening, fruit qualities remain unclear, as well as the transcriptome-wide details about the effects of sucrose on the gene expression involved in ripening-related processes. In this study, strawberry fruits at the degreening (DG), white (W), and initial-red (IR) stages were treated with different concentration of sucrose. The results showed that anthocyanin was increased while total polyphenol concentration (TPC) and total flavonoid concentration (TFC) were decreased during fruit development after sucrose treatment. Interestingly, It was showed that 100 mM sucrose application at the DG stage had the most obvious effects on fruit ripening; it made all the fruits turn into full-red (FR) around 4 days (d) earlier than the control, while it did not affect fruit quality traits and most bioactive compounds in the FR fruits. Subsequently, RNA sequencing (RNAseq) of the fruits collected at 8 days after 100 mM sucrose treatment was carried out. It was suggested that 993 genes were differentially expressed comparing with the control. Transcriptome-based expression analysis revealed that sucrose induced the expression of genes involved in the AsA and anthocyanin biosynthesis, while largely suppressed the expression of genes in TCA. The results obtained in this study provided more expression profiles of ripening-related genes under the treatment of sucrose, which will contribute to a better understanding for the mechanism underlying sucrose-induced fruit ripening.

Sugar Signaling During Fruit Ripening

“…Nevertheless, it is worth noting that in the absence of ABA, sucrose treatment had no effect on the expression of FaNCED , even if it was able to significantly upregulated the expression of FaBG. Taken together, these data suggest that sucrose level can modulate ABA content in strawberry fruit ( Luo et al., 2019 ).…”

“…As a consequence of this observation, this sugar has been proposed to induce the expression of key genes involved in ABA biosynthetic pathway, such as 9-cis-epoxycarotenid dioxygenase ( NCED ) and beta-glucosidase ( BG ) ( Jia et al., 2013 ). A recent investigation confirmed that ABA (95 µM) and sucrose (100 µM) treatments resulted in the overexpression of FaNCED1 and FaNCED2 in sprayed strawberry fruit ( Luo et al., 2019 ). Nevertheless, it is worth noting that in the absence of ABA, sucrose treatment had no effect on the expression of FaNCED , even if it was able to significantly upregulated the expression of FaBG.…”

“…Similarly, late ripening has been observed when the concentration of sucrose in orange spontaneous mutant decreased ( Zhang Y. J. et al., 2014 ). Exogenous sucrose treatment also improves strawberry ripening, accelerating the coloration of the fruit and allowing it to reach the ripe stage earlier ( Jia et al., 2011 ; Jia et al., 2013 ; Luo et al., 2019 ). As well, the effect of exogenous sucrose in harvested tomatoes at the green mature stage by accelerating ripening and postharvest processes in the fruits has been described ( Li et al., 2016 ).…”

“…However, it was recently demonstrated that the downregulation of the genes involved in the catalysis of sucrose into fructose and glucose, i.e. α-glucosidase and invertase, did not affect the expression of SUT2 ( Luo et al., 2019 ). Furthermore, no significant differences were observed in the expression of LeSUT1 , LeSUT2 , and LeSUT4 when sucrose (25 µl, 500 mM) were injected into the pedicle of tomato fruit recently harvested ( Li et al., 2016 ).…”

“…These results were concomitant with the observed increase levels of anthocyanins in mutants with enhanced content in soluble sugars and starch ( Lloyd and Zakhleniuk, 2004 ; Teng et al., 2005 ; Solfanelli et al., 2006 ). Furthermore, the interplay between sucrose and ABA brought to light the role of sugars in anthocyanin synthesis during strawberry fruit ripening ( Jia et al., 2013 ; Jia et al., 2016 ; Luo et al., 2019 ). However, it seems that sugar alone, without the presence of exogenous ABA is sufficient to trigger anthocyanin synthesis, as described in grape berries ( Dai et al., 2014 ; Olivares et al., 2017 ).…”