Traits and Gene Expression Analysis of Early and Late Ripening Pollination Constant Non-Astringent Persimmon Fruits at Different Developmental Phases

We analyzed the major fruit traits and transcriptomes between a late-ripening cultivar 'Fuyu' and an early-ripening cultivar 'Soshu' of pollination constant non-astringent persimmon (Diospyros kaki Thunb.) at different developmental stages. Sugar concentration and fruit peel color were measured every 3 weeks, until 18 weeks after full bloom (WAB) for 'Soshu' and 24 WAB for 'Fuyu'. For the sugar concentration in fruit, sucrose levels began to decline 9 weeks earlier in 'Soshu'. Fruit peel coloring progressed faster in 'Soshu', and differences in color between the cultivars were most notable at 18 WAB. Transcriptome analysis was carried out for fruit flesh every 3 weeks from 9-18 WAB. Gene ontology term analysis of the transcriptome indicated that catalytic and transport genes involved in metabolism and growth in cells and cellular organelles were mainly expressed, while in KOG and KEGG analysis, the majority of expressed genes were related to signal transduction, nuclear structure, and starch and sucrose metabolism. Differentially expressed genes were analyzed from two sets of samples: set I, in which fruits sampled at 12, 15, and 18 WAB were compared as the treatment group to the sample collected at 9 WAB as the control for each cultivar; and set II, in which fruit samples of 'Soshu' were compared as the treatment group to 'Fuyu' as the control at each WAB. For the DEGs of set I, containing three comparison combinations, the number of up-regulated genes in the treatment sample was highest at 18 WAB in 'Fuyu' and at 15 WAB in 'Soshu'. For the DEGs of set II, the number of down-regulated genes and the number of up-regulated genes were higher in 'Soshu' compared to 'Fuyu' at 12 WAB and 15 WAB, respectively. We then compared the expression patterns of fruit trait-related genes with the phenotypic changes in traits. Our results indicated that UGPase-1 and AGPase-1, involved in carbohydrate metabolism, and CRTISO and PDS, involved in carotenoid biosynthesis, may induce early fruit ripening in 'Soshu'. In addition, the transcription factors (TFs) ERF3, which binds to the promoter of ethylene-responsive genes; the MADS-box TFs RIN, AGL, and FUL; and the NAC TF controlling climacteric-type fruit ripening were considered to play a key role in controlling fruit ripening in 'Fuyu' and 'Soshu'.