Expression Analysis of a Ripening-Specific, Auxin-Repressed Endo-1,4-β-Glucanase Gene in Strawberry

A cDNA (Cel1) encoding an endo-1,4-β-glucanase (EGase) was isolated from ripe fruit of strawberry (Fragaria × 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. × ananassa, an octoploid species, and that from the diploid species Fragaria vesca indicated that the Cel1 gene is a member of a divergent multigene family. In fruit, Cel1 mRNA was first detected at the white stage of development, and at the onset of ripening, coincident with anthocyanin accumulation, Cel1 mRNA abundance increased dramatically and remained high throughout ripening and subsequent fruit deterioration. In all other tissues examined, Cel1 expression was invariably absent. Antibodies raised to Cel1 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 Cel1 mRNA accumulation were both accelerated. Conversely, auxin treatment of white fruit repressed accumulation of both Cel1 mRNA and ripening. These results indicate that strawberry Cel1 is a ripening-specific and auxin-repressed EGase, which is regulated during ripening by a decline in auxin levels originating from the achenes.