The lignification of strawberry fruit: molecular basis and effects on fruit quality

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Lignin is the second most abundant polymer found in nature after cellulose. Among the many roles lignin plays in plant growth and development are those providing structural support for land plants. Until recently, only carbohydrate polymers such as pectin and cellulose and to a lesser extent proteins such as the expansins have been regarded as structure forming and stabilizing components in fruits. Microarray analyses, however, have recently provided evidence that the expression of specific genes involved in lignin formation affect strawberry fruit firmness. As a consequence, we here propose to clone the cinnamoyl-CoA reductase (CCR), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD) genes from Fragaria x ananassa, to functionally characterize the corresponding enzymes and to determine their gene expression in different tissues. Pyrosequencing will be used for genotyping different strawberry varieties and to quantify allele frequencies in RT-PCR products. Finally, we are planning to transiently down-regulate and up-regulate CCR, CAD, and POD in fruits and to quantify the effects on fruit firmness, lignin content, and composition. Our results can be used to develop strawberry varieties with improved firmness, storage stability and thus fruit quality.