Comparison of Fruit Development, Ripening, and Transcriptome Dynamics in Taiwanese and Japanese Cultivars of Japanese Apricot (<i>Prunus mume</i> Sieb. et Zucc.)

In this study, we compared changes in traits associated with fruit development and ripening in Taiwanese and Japanese cultivars of Japanese apricot (Prunus mume Sieb. et Zucc.). We also analyzed transcriptome profiles to comprehensively examine different fruit development and ripening patterns between the two groups in terms of fruit characteristics and gene expression. Early fruit development in Taiwanese cultivars ‘ST’ and ‘Ellching’ and the Japanese cultivar ‘Hakuo’ was ahead of that in other three Japanese cultivars (P1). From late April to early May, around the stone-hardening stage, the developmental differences decreased to the same level. Thereafter, Japanese cultivars showed rapid growth, whereas Taiwanese cultivars showed slower growth, reversing the developmental differences between these lines (P2). Ethylene production was not detected until the full ripening stage and was detected for the first time at this stage in five cultivars, except for ‘Ellching’ (P3). In contrast, no ethylene production was observed during the entire duration of fruit development in ‘Ellching’. A multidimensional scaling plot showed that the overall transcriptome profile changed according to the three stages (P1–P3) of fruit development and ripening. At P1, gene ontologies (GOs) related to cell division, such as the cell cycle and regulation of cyclin-dependent protein serine/threonine kinase activity, were enriched for differentially expressed genes downregulated in Taiwanese cultivars as compared with their expression in Japanese cultivars. At P2, GOs related to fruit development were not enriched, but some genes related to phytohormones, such as auxin, abscisic acid, and cytokinin, which are associated with fruit development and ripening, were differentially expressed. At P3, the expression of genes such as ACS, ACO, and PG, which are involved in ethylene biosynthesis, increased in response to increased ethylene production, but not in ‘Ellching’, which showed no ethylene production. Expression analysis of 115 NAC (NAM-ATAF1/2-CUC2) family genes, which are related to fruit ripening and ripening date in other fruit species, in the ‘Ellching’ genome revealed changes in expression of NAC056 and NAC073 corresponding to fruit development and ripening in Taiwanese and Japanese cultivars. We discuss the differences in fruit development and ripening behaviors between Taiwanese and Japanese cultivars in terms of physiological and transcriptome changes.