Roles of heat shock proteins in tomato fruit ripening and fruit quality

Zhiping Deng, Purdue University

Abstract

Although significant progress has been made in characterizing various components of fruit ripening process, the molecular mechanisms regulating fruit texture and other attributes remain poorly understood. Using fruit juice viscosity as an indicator of cell wall solubilization and depolymerization, I tested the possibility of isolating novel genes that affect fruit quality attributes. Characterization of genes differentially expressed in thick- and thin juice tomato genotypes resulted in isolation and characterization of a small heat shock gene, designated as vis1 ( viscosity 1). My results show that vis1 transcript accumulation is negatively correlated with tomato juice thickness in different genotypes. Two alleles of vis1 exhibit genomic DNA polymorphism. Vis1-hta (vis1 -high transcript accumulator) and vis1-lta (vis1 -1ow transcript accumulator) are associated with high and low vis1 transcript accumulation, and low and high juice viscosity respectively, in diverse genotypes and in segregating progenies of lines heterogeneous for vis1 alleles. Vis1 expression is enhanced by elevated temperature and fruit ripening, and it exhibits typical chaperone activity when expressed in E. coli . Transgenic tomato plants over- and under-expressing vis1 were created to determine its role in plant growth and developmental processes, including fruit ripening. Contrary to what was expected from above studies, transgenic fruit over-expressing vis1 yielded significantly thicker juice than wild type fruit, while impaired expression of vis1 reduced juice viscosity. In addition, fruit with impaired expression of vis1 ripened earlier, had less average fruit weight. These results have provided the first genetic evidence for a stress protein regulating fruit ripening and fruit quality. To determine if expression of other classes of heat shock proteins (Hsps) is also regulated during fruit ripening, I have examined the diurnal expression of diverse heat shock genes, including members of different classes of sHsps, three Hsp70s, an Hsp90, and an Hsp100 in tomato fruit under the field conditions at a wide range of temperatures. I show herein that expression of most classes of Hsps is increased by the daytime increase in temperature under field conditions. However, transcripts accumulated more rapidly in ripening fruit than in green fruit. These results suggest that heat perception increases with fruit ripening. I propose that Hsps, including Vis1 protein, play significant roles in fruit ripening process by protecting fruit from environmental and ripening associated stresses.

Degree

Ph.D.

Advisors

Handa, Purdue University.

Subject Area

Botany|Plant propagation

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