Comparative gene expression analysis in fruits of a tomato introgression line performing higher ascorbic acid content

High levels of ascorbic acid (AsA) in tomato fruits provide health benefits for humans and also play an important role in several aspects of the plant life. Although AsA metabolism has been characterized in detail, the genetic mechanisms controlling AsA accumulation in tomatoes are poorly understood. We used an introgression line (IL 12-4) containing a QTL promoting AsA accumulation in the fruit and carried out a comparative transcriptomic analysis of fruit tissue using a parental cultivar (M82) with low AsA levels as a reference. We identified 253 differentially expressed genes, indicating that AsA accumulation in IL 12-4 reflects a combination of increased metabolic flux and reduced utilization of AsA. Evidences coming from the experiment suggest that AsA accumulation in IL 12-4 fruit is mainly achieved by increasing flux through the L-galactonic acid pathway, which is driven by pectin degradation and may be triggered by ethylene. Comparative microarray analysis between a tomato introgression line (IL 12-4) expressing higher level of fruit ascorbic acid and its parental cultivar M82 (reference) was performed. In particular, samples were generated by pooling red-ripe fruit from the same plant and discarding the seeds, jelly parenchyma, columella and placenta tissues. Three plant replica were used for each line (IL 12-4 and M82) and the experiment was replicated over two consecutive years.