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

木质素是自然界中发现的第二丰富的聚合物，仅次于纤维素。木质素在植物生长发育中起着许多作用，其中包括为陆地植物提供结构支持。直到最近，只有碳水化合物聚合物，如果胶和纤维素，以及较少程度的蛋白质，如膨胀蛋白，被认为是水果中形成结构和稳定的成分。然而，微阵列分析最近提供的证据表明，参与木质素形成的特定基因的表达影响草莓果实的硬度。因此，本研究拟克隆肉桂酰辅酶a还原酶（CCR）、肉桂醇脱氢酶（CAD）和过氧化物酶（POD）基因，对相应酶进行功能表征，并测定其在不同组织中的基因表达。焦磷酸测序将用于不同草莓品种的基因分型，并定量RT-PCR产品中的等位基因频率。最后，我们计划在水果中瞬时下调和上调CCR、CAD和POD，并量化对果实硬度、木质素含量和成分的影响。我们的研究结果可用于培育硬度、贮藏稳定性和果实品质更好的草莓品种。

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.