Gene Expression, Hormone Signaling, and Nutrient Uptake in the Root Regermination of Grafted Watermelon Plants with Different Pumpkin Rootstocks

Roots play a crucial role in plant growth by absorbing various nutrients from soils. However, the gene expression in the lateral root regermination of pumpkin rootstocks by double-root-cutting grafting remains unclear. In this study, transcriptome sequencing was performed to analyze the nutrient uptake, hormones, and differentially expressed genes (DEGs) during the lateral root formation of rootstocks (F5, F1, and DM) after grafting with watermelon. Results showed that the ability of root regermination varied in the three rootstocks. F1 had the highest root length, whereas DM had the shortest roots after cutting the main roots, suggesting that F1 had the best capacity to form lateral roots. An increased trend of nutrient uptake (N, Mg 2+ , and K) was observed. However, the P content decreased after root cutting in the three rootstocks. Meanwhile, grafted watermelon plants exhibited different abilities to adsorb nutrient elements with the three rootstocks. Three hormones (indole acetic acid, salicylic acid, and jasmonic acid) were involved in root development, and the highest amounts of salicylic acid were observed. The most significant metabolic pathways involved the mechanisms of signal transduction, secondary metabolite biosynthesis, carbohydrate transport, and cell wall biogenesis. DEGs were also related to the functions of the membrane and response to organic substances, chitin, and wounding. Our results provide a new understanding of root regermination and elucidate a potential gene expression for the regulation and improvement of the root system in grafted plants with pumpkin rootstocks.