Molecular Dissection of Sensory Traits in the Potato Tuber

Abstract

The aim of this research was to increase understanding of tuber sensory traits such as tuber color and flavor. For tuber color the focus was on tuber carotenoid content. Using metabolic engineering approaches it was discovered that it was possible to enhance considerably the amount and types of carotenoid that could accumulate in potato tubers. Transgenic lines based on three genes, the Erwinia crtb gene, encoding phytoene synthase, the Escherichia coli dxs gene encoding 1-deoxy-D-xylulose 5-phosphate synthase and the β-carotene ketolase gene (bkt1) from the unicellular green alga Haematococcus pluvialis were developed. Plastid-targeted, tuber-specific expression of each of these transgenes was achieved and each lead to modified carotenoid content in the tuber. The crtB transgenic lines contained up to six-fold higher levels of total carotenoid and also accumulated nutritionally significant levels of the pro-vitamin A carotenoid, β-carotene, a carotenoid that is not normally found in potato tubers. The transformation of Solanum tuberosum spp. phureja (Phureja) tubers with the bkt1 gene, lead to the accumulation of the carotenoid astaxanthin, which gave the tubers an orange/pink appearance. Tuber flavor studies were based on the comparison of Phureja tubers with S. tuberosum spp. tuberosum (Tuberosum) tubers, as the Phureja tubers consistently scored higher in professional sensory evaluation panels. Measurement of the major umami compounds in tubers from several cultivars of Phureja and Tuberosum, showed consistently higher levels in the Phureja tubers, and it is hypothesised that this is an important contributor to potato flavor.Resumen El propósito de esta investigación fue incrementar el conocimiento de los caracteres sensoriales tales como color y sabor del tubérculo. Para el color se usó el contenido carotenoide del tubérculo. Por medio de ingeniería metabólica se descubrió que era posible elevar considerablemente la cantidad y tipos de caroteno que se pueden acumular en los tubérculos de papa. Se desarrollaron líneas transgénicas basadas en tres genes, el gen Erwinia crtb que codifica fitoteno sintasa, el gen Escherichia coli dxs que codifica 1-deoxi-D-xilulosa 5-fosfato sintasa y el gen β-caroteno ketolasa (bkt1) del alga verde unicelular Haematococcus pluvialis. De cada uno de estos transgenes se logró una expresión, dirigida al plastidio, especifica del tubérculo y cada uno condujo a un contenido modificado de carotenoides en el tubérculo. Las líneas transgénicas crtbB contenían niveles hasta 6 veces más altos de carotenoides totales y también acumularon niveles nutricionales significativos del carotenoide provitamina A, β-caroteno, un carotenoide que no se encuentra normalmente en tubérculos de papa. La transformación de tubér-culos de Solanum tuberosum spp. phureja (Phureja) con el gen bkt1 condujeron a la acumulación del carotenoide astaxantina, el cual dio a los tubérculos apariencia anaranjada/rosada. Los estudios sobre sabor se basaron en la comparación de tubérculos de phureja con los de S. tuberos...