Molecular aspects of the strawberry fruit softening

Abstract

Summary Download : Download full-size image The involvement of endo-s-1, 4-glucanases (EGases, EC 3.2.1.4) in the ripening of strawberry fruits has been investigated by means of structural, biochemical, molecular and cytological techniques. Endo-s-1, 4-glucanase activity starts to be detectable at the end of fruit cells expansion (i.e. large green stage), has a steep increase during the ripening process and reaches a maximum in red fruits. It is caused by two different isoforms both increasing along the ripening process. Two full-length cDNA clones (faEG1 and faEG3) coding for divergent EGases have been obtained by screening a library representing transcripts from red strawberry fruits. The transcripts related to the two cDNAs accumulate during ripening, however faEG3 related mRNA can also be detected, although at very low levels, in green berries and in other green developing tissues. In fruits, both transcripts are down-regulated by exogenous application of an auxin analogue (1-naphthalene acetic acid), thus confirming that auxin has a fundamental role in the ripening of the non-climacteric strawberry. The protein encoded by faEG3 has an extra peptide of about 130 amino acids at its C-termi-nus. In particular, this peptide shows striking homologies to the cellulose binding domains of some microbial cellulases. The structural and cytological findings are well in agreement with the expression pattern of the two different endo-s-1,4-glucanases during the ripening of strawberry fruits.