A Novel Small Heat Shock Protein Gene,vis1, Contributes to Pectin Depolymerization and Juice Viscosity in Tomato Fruit

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Abstract
We have characterized a novel small heat shock protein gene,viscosity 1 (vis1) from tomato (Lycopersicon esculentum) and provide evidence that it plays a role in pectin depolymerization and juice viscosity in ripening fruits. Expression of vis1 is negatively associated with juice viscosity in diverse tomato genotypes. vis1exhibits DNA polymorphism among tomato genotypes, and the alleles vis1-hta (high-transcript accumulator; accession no. AY128101) andvis1-lta (low transcript accumulator; accession no. AY128102) are associated with thinner and thicker juice, respectively. Segregation of tomato lines heterogeneous forvis1 alleles indicates that vis1influences pectin depolymerization and juice viscosity in ripening fruits. vis1 is regulated by fruit ripening and high temperature and exhibits a typical heat shock protein chaperone function when expressed in bacterial cells. We propose that VIS1 contributes to physiochemical properties of juice, including pectin depolymerization, by reducing thermal denaturation of depolymerizing enzymes during daytime elevated temperatures.