Metabolite Profile of Xylem Sap in Cotton Seedlings Is Changed by K Deficiency

Integrated transcriptomic and metabolomic analyses reveal key metabolic pathways in response to potassium deficiency in coconut (Cocos nucifera L.) seedlings

Potassium ions (K⁺) are important for plant growth and crop yield. However, the effects of K⁺ deficiency on the biomass of coconut seedlings and the mechanism by which K⁺ deficiency regulates plant growth remain largely unknown. Therefore, in this study, we compared the physiological, transcriptome, and metabolite profiles of coconut seedling leaves under K⁺-deficient and K⁺-sufficient conditions using pot hydroponic experiments, RNA-sequencing, and metabolomics technologies. K⁺ deficiency stress significantly reduced the plant height, biomass, and soil and plant analyzer development value, as well as K content, soluble protein, crude fat, and soluble sugar contents of coconut seedlings. Under K⁺ deficiency, the leaf malondialdehyde content of coconut seedlings were significantly increased, whereas the proline (Pro) content was significantly reduced. Superoxide dismutase, peroxidase, and catalase activities were significantly reduced. The contents of endogenous hormones such as auxin, gibberellin, and zeatin were significantly decreased, whereas abscisic acid content was significantly increased. RNA-sequencing revealed that compared to the control, there were 1003 differentially expressed genes (DEGs) in the leaves of coconut seedlings under K⁺ deficiency. Gene Ontology analysis revealed that these DEGs were mainly related to "integral component of membrane," "plasma membrane," "nucleus", "transcription factor activity," "sequence-specific DNA binding," and "protein kinase activity." Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that the DEGs were mainly involved in "MAPK signaling pathway-plant," "plant hormone signal transduction," "starch and sucrose metabolism," "plant-pathogen interaction," "ABC transporters," and "glycerophospholipid metabolism." Metabolomic analysis showed that metabolites related to fatty acids, lipidol, amines, organic acids, amino acids, and flavonoids were generally down-regulated in coconut seedlings under K⁺ deficiency, whereas metabolites related to phenolic acids, nucleic acids, sugars, and alkaloids were mostly up-regulated. Therefore, coconut seedlings respond to K⁺ deficiency stress by regulating signal transduction pathways, primary and secondary metabolism, and plant-pathogen interaction. These results confirm the importance of K⁺ for coconut production, and provide a more in-depth understanding of the response of coconut seedlings to K⁺ deficiency and a basis for improving K⁺ utilization efficiency in coconut trees.

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08870-5.

Polyamine Metabolism in Scots Pine Embryogenic Cells under Potassium Deficiency

Polyamines (PA) have a protective role in maintaining growth and development in Scots pine during abiotic stresses. In the present study, a controlled liquid Scots pine embryogenic cell culture was used for studying the responses of PA metabolism related to potassium deficiency. The transcription level regulation of PA metabolism led to the accumulation of putrescine (Put). Arginine decarboxylase (ADC) had an increased expression trend under potassium deficiency, whereas spermidine synthase (SPDS) expression decreased. Generally, free spermidine (Spd) and spermine (Spm)/ thermospermine (t-Spm) contents were kept relatively stable, mostly by the downregulation of polyamine oxidase (PAO) expression. The low potassium contents in the culture medium decreased the potassium content of the cells, which inhibited cell mass growth, but did not affect cell viability. The reduced growth was probably caused by repressed metabolic activity and cell division, whereas there were no signs of H₂O₂-induced oxidative stress or increased cell death. The low intracellular content of K⁺ decreased the content of Na⁺. The decrease in the pH of the culture medium indicated that H⁺ ions were pumped out of the cells. Altogether, our findings emphasize the specific role(s) of Put under potassium deficiency and strict developmental regulation of PA metabolism in Scots pine.