Expression analysis of a ripening-specific, auxin-repressed endo-1,4-β-glucanase gene in strawberry

A cDNA (Cel1) encoding an endo-1,4-beta-glucanase (EGase) was isolated from ripe fruit of strawberry (Fragaria x ananassa). The deduced protein of 496 amino acids contains a presumptive signal sequence, a common feature of cell wall-localized EGases, and one potential N-glycosylation site. Southern- blot analysis of genomic DNA from F. x ananassa, an octoploid species, and that from the diploid species Fragaria vesca indicated that the Cell gene is a member of a divergent multigene family. In fruit, Cell mRNA was first detected at the white stage of development, and at the onset of ripening, coincident with anthocyanin accumulation, Cell mRNA abundance increased dramatically and remained high throughout ripening and subsequent fruit deterioration. In all other tissues examined, Cell expression was invariably absent. Antibodies raised to Cell protein detected a protein of 62 kD only in ripening fruit. Upon deachenation of young white fruit to remove the source of endogenous auxins, ripening, as visualized by anthocyanin accumulation, and Cell mRNA accumulation were both accelerated. Conversely, auxin treatment of white fruit repressed accumulation of both Cell mRNA and ripening. These results indicate that strawberry Cell is a ripening-specific and auxin-repressed EGase, which is regulated during ripening by a decline in auxin levels originating from the achenes.