β-galactosidases with a lectin-like domain are expressed in strawberry

Strawberry fruits (Fragaria x ananassa Duch.) undergo a marked softening during their ripening, and the process is accompanied by a release of free sugars with galactose among them. In this work total beta -galactosidase activity was measured in cell wall proteins from strawberry fruits at different developmental stages. Three full-length cDNAs (Fa beta gal1, Fa beta gal2 and Fa beta gal3, respectively) encoding different beta -galactosidases (EC 3.2.1.23) were isolated from a library representing red fruit transcripts. All of them could be detected both in fruits and in vegetative tissues. However, only Fa beta gal1 showed an increasing expression during the ripening stages up to a maximum in the red fruits, while the other two (Fa beta gal2 and Fa beta gal3) were mostly found in green fruits and became barely detectable during ripening proper. The three beta -galactosidase-encoding cDNAs; were expressed in the yeast Pichia pastoris, and it was thus possible to demonstrate that each of them encode a beta -galactosidase. The expression of the three beta -galactosidase genes appears to be downregulated by auxin, as already observed for other ripening-related genes of the non-climacteric strawberry. An unusual characteristic of two strawberry beta -galactosidases (Fa beta gal1 and Fa beta gal2) is that at the C-terminus of the enzymes a domain is found which is structurally related to known animal peptides with a sugar-binding ability.