A class IV chitinase is highly expressed in grape berries during ripening

Chitinase activity increased markedly at the onset of ripening in grape (Vitis vinifera L.) berries and continued to increase throughout the sugar accumulation phase of berry development. In contrast, beta-1,3-glucanase activity was not detected in grape berries at any stage of development. Two closely related chitinase cDNAs (VvChi4A and VvChi4B) were cloned from grapes. Sequence and Southern analysis indicate that these two clones may represent alleles of the same gene. The predicted proteins are acidic and have a signal peptide followed by a cysteine-rich, chitin-binding domain and a catalytic region. An analysis of their sequences indicates that they are class IV chitinases. The deduced protein sequence of VvChi4A has a high level of identity with the 32- and 28-kD chitinases present as haze proteins in wine. Expression of VvChi4 was high in berries and low in flowers but was not detected in leaves, roots, or seeds. No expression was detected in berries 2 to 8 weeks postflowering, but expression was high 12 to 16 weeks postflowering, which coincided with sugar accumulation and an increase in chitinase activity. Constitutive expression of VvChi4 appears to be fruit-specific and induced at high levels in grapes during ripening.