Analysis of Expressed Sequence Tags from Rapidly Softened Pulp of Persimmon (Diospyros kaki Thunb.)

To improve our understanding of the molecular mechanism of rapid softening of persimmon (Diospyros kaki) 'Saijo' fruit on the tree prior to harvest, we constructed a cDNA library from softened pulp of immature fruit and analyzed expressed sequence tags (ESTs). Fruits that were rapidly softened on the tree were harvested at three softening index (from moderately soft to over-ripe) in early October. We sequenced 5728 randomly selected clones from the library, and obtained a total of 4701 ESTs (FY982194-FY986894). Following a sequence homology search, sequences for two 1-aminocyclopropane-1-carboxylate (ACC) synthase (Dk-ACS2 and Dk-ACS3) and two ACC oxidase (Dk-ACO1 and Dk-ACO2) cDNAs were isolated, as well as genes for pectinase, hemicellulase and cellulose-interacting protein. Notably, the beta-D-galactosidase, xyloglucan endotransglycosylase (XTH), and expansin genes isolated from fruit rapidly softened on the tree showed sequence differences compared with those isolated previously from the ovary and young expanding fruit. One of the isolated genes, Dk-XTH1, was ethylene-dependent. These results suggest that rapid softening of persimmon fruit on the tree is related to ethylene synthesis and hemicellulose degradation. This study provides an initial overview of a set of genes that are expressed during softening of persimmon fruit.