Metabolic response and correlations between ions and metabolites in Phragmites communis under long-term salinity toxicity

Exogenous proline suppresses endogenous proline and proline-production genes but improves the salinity tolerance capacity of salt-sensitive rice by stimulating antioxidant mechanisms and photosynthesis

Salinity is a critical environmental stress factor that significantly reduces crop productivity and yield. A mutant B-type response regulator gene (hst1) has been shown to promote salinity tolerance in the YNU genotype. Previous studies on the hst1 gene showed a higher proline production capacity under salt stress. Using almost identical genetic backgrounded salt-tolerant (YNU) and salt-sensitive (Sister line) rice genotypes, we tested the function of proline in the hst1 gene salinity-tolerance mechanism by applying exogenous proline under control and salt-stress conditions. Morpho-physiological, biochemical, and molecular analysis of ST and SS plants was performed to clarify the salinity tolerance mechanism mediated by the exogenous proline. The ST and SS genotypes accumulated exogenous proline, and the ST genotype has higher proline levels than the SS genotype. However, exogenous proline improved salt tolerance only in the SS genotype. Exogenous proline promotes plant and root growth by stimulating photosynthetic pigments and photosynthesis. The exogenous proline has a reductive effect on MDA, and H2O2 protects plants against ROS. Interestingly, exogenous proline lowers Na+ and raises K+ accumulations under salt stress. In the SS genotype, exogenous proline increases the activity of antioxidant enzymes (SOD, CAT, and APX) to protect against salinity-induced damage. The exogenous proline application down-regulates proline-synthesis genes (OsP5CS1 and OsP5CR) and up-regulates proline-degradation genes. Also, exogenous proline increases the expression of the OsSalT and OsGRAS29 genes, improving salinity tolerance in the SS genotype. Our study has demonstrated that proline plays a significant role in conferring salt tolerance with the salinity-tolerance-related hst1 mechanisms.

Metabolomic Evenness Underlies Intraspecific Differences Among Lineages of a Wetland Grass

The metabolome represents an important functional trait likely important to plant invasion success, but we have a limited understanding of whether the entire metabolome or targeted groups of compounds confer an advantage to invasive as compared to native taxa. We conducted a lipidomic and metabolomic analysis of the cosmopolitan wetland grass Phragmites australis. We classified features into metabolic pathways, subclasses, and classes. Subsequently, we used Random Forests to identify informative features to differentiate five phylogeographic and ecologically distinct lineages: European native, North American invasive, North American native, Gulf, and Delta. We found that lineages had unique phytochemical fingerprints, although there was overlap between the North American invasive and North American native lineages. Furthermore, we found that divergence in phytochemical diversity was driven by compound evenness rather than metabolite richness. Interestingly, the North American invasive lineage had greater chemical evenness than the Delta and Gulf lineages but lower evenness than the North American native lineage. Our results suggest that metabolomic evenness may represent a critical functional trait within a plant species. Its role in invasion success, resistance to herbivory, and large-scale die-off events common to this and other plant species remain to be investigated.

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.

Transcriptional and Metabolic Responses of Maize Shoots to Long-Term Potassium Deficiency

Potassium is important for plant growth and crop yield. However, the effects of potassium (K⁺) deficiency on silage maize biomass yield and how maize shoot feedback mechanisms of K⁺ deficiency regulate whole plant growth remains largely unknown. Here, the study aims to explore the maize growth, transcriptional and metabolic responses of shoots to long-term potassium deficiency. Under the K⁺ insufficiency condition, the biomass yield of silage maize decreased. The transcriptome data showed that there were 922 and 1,107 differential expression genes in DH605 and Z58, respectively. In the two varieties, 390 differently expressed overlapping genes were similarly regulated. These genes were considered the fundamental responses to K⁺ deficiency in maize shoots. Many stress-induced genes are involved in transport, primary and secondary metabolism, regulation, and other processes, which are involved in K⁺ acquisition and homeostasis. Metabolic profiles indicated that most amino acids, phenolic acids, organic acids, and alkaloids were accumulated in shoots under K⁺ deficiency conditions and part of the sugars and sugar alcohols also increased. It revealed that putrescine and putrescine derivatives were specifically accumulated under the K⁺ deficiency condition, which may play a role in the feedback regulation of shoot growth. These results confirmed the importance of K⁺ on silage maize production and provided a deeper insight into the responses to K⁺ deficiency in maize shoots.

Metabolics and ionomics responses of tea leaves (Camellia sinensis (L.) O. Kuntze) to fluoride stress

Tea plant (Camellia sinensis (L.) O. Kuntze) is known to accumulate high concentrations of fluoride (F) in its leaves; however, the underlying mechanism of F accumulation remains unclear. The main objective of this study was to investigate the homeostatic self-defense mechanisms of tea leaves to F supplementation (0, 5, 20, and 50 mgL^-1) by metabolomics and ionomics. We identified a total of 96 up-regulated and 40 down-regulated metabolites in tea leaves treated with F. Of these different compounds, minor polypeptides, carbohydrates and amino acids played valuable roles in the F-tolerating mechanism of tea plant. After F treatments, the concentrations of sodium (Na), ferrum (Fe), manganese (Mn), and molybdenum (Mo) were significantly increased in tea leaves, whereas the aluminum (Al) was decreased. These findings suggest that the ionic balance and metabolites are attributable to the development of F tolerance, providing new insight into tea plant adaptation to F stress.