Transcriptome analysis of sweet potato responses to potassium deficiency.

Background: As one of three essential nutrients, potassium is regarded as a main limiting factor for growth and development in plant. Sweet potato (Ipomoea batatas L.) is one of seven major food crops grown worldwide, and is both a nutrient-rich food and a bioenergy crop. It is a typical 'K-favoring' crop, and the level of potassium ion (K) supplementation directly influences its production. However, little is known about the transcriptional changes in sweet potato genes under low-K conditions. Here, we analyzed the transcriptomic profiles of sweet potato roots in response to K deficiency to determine the effect of low-K stress on this economically important crop.

Results: The roots of sweet potato seedlings with or without K treatment were harvested and used for transcriptome analyses. The results showed 559 differently expressed genes (DEGs) in low and high K groups. Among the DEGs, 336 were upregulated and 223 were downregulated. These DEGs were involved in transcriptional regulation, calcium binding, redox-signaling, biosynthesis, transport, and metabolic process. Further analysis revealed previously unknow genes involved in low-K stress, which could be investigated further to improve low K tolerance in plants. Confirmation of RNA-sequencing results using qRT-PCR displayed a high level of consistency between the two experiments. Analysis showed that many auxin-, ethylene- and jasmonic acid-related genes respond to K deficiency, suggesting that these hormones have important roles in K nutrient signaling in sweet potato.

Conclusions: According to the transcriptome data of sweet potato, various DEGs showed transcriptional changes in response to low-K stress. However, the expression level of some kinases, transporters, transcription factors (TFs), hormone-related genes, and plant defense-related genes changed significantly, suggesting that they have important roles during K deficiency. Thus, this study identifies potential genes for genetic improvement of responses to low-K stress and provides valuable insight into the molecular mechanisms regulating low K tolerance in sweet potato. Further research is required to clarify the function of these DEGs under low-K stress.