Differential Anthocyanin Concentrations and Expression of Anthocyanin Biosynthesis Genes in Strawberry ‘Sachinoka’ during Fruit Ripening under High-temperature Stress

Fruit color is an important factor in fruit quality. Anthocyanins are common pigments that accumulate in many fruits, including grape, apple, and strawberry. The regulation of their biosynthesis has been studied widely and frequently (review in Jaakola, 2013). In particular, UFGT (UDP-glucose: flavonoid 3-O-glucosyltransferase) plays an important role in anthocyanin biosynthesis in grape (Boss et al., 1996; Kobayashi, 2009), and FaMYB10 regulates the expression of FaUFGT in strawberry (Medina-Puche et al., 2014; Kadomura-Ishikawa et al., 2015a). It is well known that anthocyanin accumulation in fruits is affected by temperature, and is decreased when fruits are grown at high temperature (Saure, 1990; Ikeda et al., 2011). Recently, we demonstrated that the anthocyanin concentration and the expression of genes related to anthocyanin biosynthesis decreased in strawberry ‘Sachinoka’ fruits grown at high temperature (Matsushita et al., 2016). In grape, high temperature inhibits anthocyanin accumulation by reducing the activity of UFGT (Mori et al., 2004). In apple, rapidly reduces the expression of the R2R3MYB transcription factor (TF) gene (MYB10), which regulates the coordination of red skin coloration (Lin-Wang et al., 2011). Although high temperature stress could occur at any time during fruit coloring, published studies of the effect on anthocyanin biosynthesis applied high temperature throughout the coloring period (Mori et al., 2004; Matsushita et al., 2016), but not at different ripening stages. There are two studies examined the effect of temperature on coloring in grapes and rose: Yamane et al. (2006) investigated the temperature-sensitive stages for coloration and the mechanisms that underlie the effect of temperature on anthocyanin accumulation using 2-week treatments at 20 and 30°C. Then, they elucidated that stage3 (from one to three weeks after the onset of coloring) is the most sensitive for anthocyanin accumulation in the berry skins of ‘Aki Queen’. Dela et al. (2003) described the effect of transient high temperature on the concentration and composition of anthocyanins in ‘Jaguar’ rose flowers, and showed that although a 1-d high temperature treatment (39/18°C day/ night) had no effect on pigmentation, a 3-d treatment had a substantial effect on pigmentation due to decreasing anthocyanin accumulation. However, we cannot find any report of the effect of applying high temperature at different coloring stages or of the relationship between anthocyanin concentration and the expression of genes related to anthocyanin biosynthesis in strawberry. Therefore, we designed two experiments to explore this. Experiment 1 investigated the influence of high air temperature (30/15°C) on anthocyanin biosynthesis at different coloring stages. Experiment 2 examined the effect of high air temperature in fruits exposed to the high temperature at different coloring stages and harvested when fully ripe.