Karppinen Katja, Tegelberg Pinja, Häggman Hely, Jaakola Laura
Department of Ecology and Genetics, University of Oulu, Oulu, Finland.
Climate laboratory Holt, Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway.
Front Plant Sci. 2018 Aug 29;9:1259. doi: 10.3389/fpls.2018.01259. eCollection 2018.
Ripening of non-climacteric bilberry ( L.) fruit is characterized by a high accumulation of health-beneficial anthocyanins. Plant hormone abscisic acid (ABA) and sucrose have been shown to be among the central signaling molecules coordinating non-climacteric fruit ripening and anthocyanin accumulation in some fruits such as strawberry. Our earlier studies have demonstrated an elevation in endogenous ABA level in bilberry fruit at the onset of ripening indicating a role for ABA in the regulation of bilberry fruit ripening. In the present study, we show that the treatment of unripe green bilberry fruits with exogenous ABA significantly promotes anthocyanin biosynthesis and accumulation both in fruits attached and detached to the plant. In addition, ABA biosynthesis inhibitor, fluridone, delayed anthocyanin accumulation in bilberries. Exogenous ABA also induced the expression of several genes involved in cell wall modification in ripening bilberry fruits. Furthermore, silencing of , the key gene in ABA biosynthesis, was accompanied by the down-regulation in the expression of key anthocyanin biosynthetic genes. In contrast, the treatment of unripe green bilberry fruits with exogenous sucrose or glucose did not lead to an enhancement in the anthocyanin accumulation neither in fruits attached to plant nor in post-harvest fruits. Moreover, sugars failed to induce the expression of genes associated in anthocyanin biosynthesis or ABA biosynthesis while could elevate expression of some genes associated with cell wall modification in post-harvest bilberry fruits. Our results demonstrate that ABA plays a major role in the regulation of ripening-related processes such as anthocyanin biosynthesis and cell wall modification in bilberry fruit, whereas sugars seem to have minor regulatory roles in the processes. The results indicate that the regulation of bilberry fruit ripening differs from strawberry that is currently considered as a model of non-climacteric fruit ripening. In this study, we also identified transcription factors, which expression was enhanced by ABA, as potential regulators of ABA-mediated bilberry fruit ripening processes.
非跃变型越橘（Vaccinium myrtillus L.）果实成熟的特点是对健康有益的花青素大量积累。植物激素脱落酸（ABA）和蔗糖已被证明是协调非跃变型果实成熟和某些果实（如草莓）中花青素积累的核心信号分子。我们早期的研究表明，越橘果实成熟开始时内源ABA水平升高，表明ABA在越橘果实成熟调控中发挥作用。在本研究中，我们发现用外源ABA处理未成熟的绿色越橘果实，无论是在植株上的果实还是离体果实中，都能显著促进花青素的生物合成和积累。此外，ABA生物合成抑制剂氟啶酮延缓了越橘中花青素的积累。外源ABA还诱导了成熟越橘果实中几个参与细胞壁修饰的基因的表达。此外，ABA生物合成关键基因的沉默伴随着花青素生物合成关键基因表达的下调。相反，用外源蔗糖或葡萄糖处理未成熟的绿色越橘果实，无论是在植株上的果实还是采后果实中，都不会导致花青素积累增加。此外，糖类未能诱导花青素生物合成或ABA生物合成相关基因的表达，而糖类可以提高采后越橘果实中一些与细胞壁修饰相关基因的表达。我们的结果表明，ABA在越橘果实成熟相关过程（如花青素生物合成和细胞壁修饰）的调控中起主要作用，而糖类在这些过程中的调控作用似乎较小。结果表明，越橘果实成熟的调控与目前被视为非跃变型果实成熟模型的草莓不同。在本研究中，我们还鉴定了一些转录因子，其表达受ABA增强，作为ABA介导的越橘果实成熟过程的潜在调节因子。
