Transcriptomic analyses of sweet potato in response to Cd exposure and protective effects of K on Cd-induced physiological alterations

We aimed to understand the molecular mechanism of differential cadmium (Cd) accumulation in two cultivars of sweet potato and to clarify the effects of potassium (K) supply on Cd accumulation. Comparative transcriptomes were employed to identify key genes and pathways using a low-Cd (N88) and a high-Cd cultivar (X16) in a pot experiment. The antioxidant capacity and cell wall components of root tips were analyzed to account for the effect of K regulating Cd accumulation in N88 via a hydroponic experiment. Transcriptome analysis revealed that 29 and 20 genes were differentially expressed in N88 and X16, respectively, when comparing the control with the two Cd treatments. X16 had more differentially expressed genes (DEGs), including 2649 common up-regulated and 3173 common down-regulated than N88 in any treatment. GO and KEGG analyses showed that the DEGs were assigned and enriched in different pathways. Some critical DEGs such as PDR, HMA3, COPT5, CAX3, GAUT, CCR, AUX1, CAT, SOD, GSR, and GST were identified. The DEGs were involved in pathways including heavy metal transport or detoxification, cell wall biosynthesis, plant hormone signal transduction, and glutathione metabolism. Additionally, K supply substantially decreased Cd accumulation and reactive oxygen species production and promoted the production of cellulose, pectin and lignin in the root tips when exposed to Cd. Several critical DEGs associated with heavy metal transport and cell wall biosynthesis were responsible for the difference of Cd accumulation between the two cultivars. Application of K could help decrease Cd accumulation in sweet potato.