Elucidating the genomics of nutritional and morphological traits in watercress (Nasturtium officinale R. Br.): The first genomic resources

Abstract

Watercress (Nasturtium officinale R. Br.; Brassicaceae) has a long history of human use for medicine and consumption. In recent years, it has received a large deal of attention as one of the most nutrient-dense foods. Despite this, watercress remains largely underdeveloped with limited breeding resources through which to meet current and future intensifying market demands, such as for a more compact morphology, enhanced nutritional benefits and resource-use efficiency. The aim of this PhD has been to characterize the genetic structure of nutritional and morphological traits in watercress and develop molecular breeding tools that will inform and facilitate future work on this crop. To this end, Chapter 1 provides an overview of pre-existing knowledge on watercress and reviews the opportunities offered by Next Generation Sequencing tools for undeveloped crops. Chapter 2 describes the application of RNASeq towards de novo assembly and functional annotation the watercress transcriptome for the first time. Differential expression analysis resulted in a catalogue of significant genes for antioxidant capacity and glucosinolate content in watercress and identified orthologs to known phenylpropanoid and glucosinolate biosynthetic pathway genes. In Chapter 3, the first genetic linkage map and QTL analysis were completed for this crop, utilizing Genotyping-By-Sequencing for marker discovery. In a novel undertaking to identify QTL for chemopreventive qualities in a plant genome, the toxicity of watercress to human cancer cells was mapped successfully explaining 20 % of variation in this trait. As the development of new cultivars remains central to this work, Chapter 4 reports on the first commercial trials of the new ‘Boldrewood’ accession, aimed at informing its commercialization process. Excitingly, this study also highlighted previously unknown trends in phytonutrient character of the crops across a temporal gradient, which suggests the potential for increasing consumer health benefit by alternations to crop management practices. The sum of this work has resulted in significant advances in the understanding of watercress genetics and genomics and the production of valuable resources for its future preservation and advancement.

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ORCID for Mark Chapman: orcid.org/0000-0002-7151-723X

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