Cucurbitacin Profile and Metalloid Stress Response in Cucurbita pepo L. Upon Arsenic Exposure.

Abstract

Cucurbits are cultivated worldwide in regions with high concentrations of arsenic (As), a hazardous metalloid, affecting produce quality and increasing the consumer exposure. Cucurbitacins are herbivore-deterrent secondary metabolites that contribute to the plant defense response. The impact of As exposure on phenotypic and metabolic traits has not been studied in members of the Cucurbitaceae family, such as squash (Cucurbita pepo L.). To comprehend the effects of As on the root system of C. pepo, we assessed phenotype, cucurbitacin content, and transcriptome under low and high As concentrations. We report that at low dosages, cucurbitacins are decreased, while growth is not significantly affected. Conversely, high dosages impact growth and development altering root phenotype but cucurbitacin content is not significantly different from untreated plants. Furthermore, gene ontology enrichment on results of the RNA-seq analysis indicate that high dosages of As affect cellular regulatory processes, with genes related to glutathione metabolism being of the most upregulated. Additionally, an in-depth analysis of orthologs members of the heavy metal-associated (HMA)-domain superfamily and As-related transporters suggest a dosage-dependent participation of key members. WGCNA analysis reveals As-specific gene co-expression modules, indicating that low As levels induce adaptive responses in energy and allantoin metabolism, while higher levels trigger intensified oxidative stress responses, including upregulation of MYB transcription factors and heat shock proteins, which may support tolerance to the metalloid. Overall, As influences the root system physiology and metabolism in a concentration-specific manner, highlighting key defense systems and genes involved in C. pepo response to As exposure.