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

Abstract

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 β-galactosidase activity was measured in cell wall proteins from strawberry fruits at different developmental stages. Three full-length cDNAs (Faβgal1, Faβgal2 and Faβgal3, respectively) encoding different β-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 Faβgal1 showed an increasing expression during the ripening stages up to a maximum in the red fruits, while the other two (Faβgal2 and Faβgal3) were mostly found in green fruits and became barely detectable during ripening proper. The three β-galactosidase-encoding cDNAs were expressed in the yeast Pichia pastoris, and it was thus possible to demonstrate that each of them encode a β-galactosidase. The expression of the three β-galactosidase genes appears to be down-regulated by auxin, as already observed for other ripening-related genes of the non-climacteric strawberry. An unusual characteristic of two strawberry β-galactosidases (Faβgal1 and Faβgal2) 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.