Metabolome refers to the collection of all small molecule metabolites (primarily endogenous small molecules with a relative molecular weight of less than 1000) in cells, tissues, organs, or organisms. Metabolomics follows the research principles of genomics and proteomics, quantitatively analyzing all metabolites in the organism and seeking to understand their relative relationship with physiological and pathological changes. It is a component of systems biology. Targeted metabolomics follows the principles and ideas of metabolomics, analyzing and studying a limited number or classes of biologically relevant metabolites. It is usually used to further confirm differences in metabolites discovered by non-targeted metabolomics.
Currently, there are two main strategies for metabolomics analysis: non-targeted metabolomics and targeted metabolomics. Each method has its own advantages and disadvantages. Non-targeted metabolomics detects all measurable metabolites, including unknown compounds. Due to the comprehensiveness of non-targeted metabolomics data, statistical analysis is needed for data processing, such as multivariate analysis, in order to extract useful differential data from the vast amount of data. These differential signals need to be annotated in experiments or databases and identified using analytical chemistry techniques. Non-targeted metabolomics provides opportunities to discover new targets, but the metabolome coverage is limited by the sensitivity inherent in the sample preparation method and analytical technology. The main challenges of non-targeted metabolomics are the time-consuming process of collecting raw data, difficulties in identifying and characterizing unknown metabolites, and the fact that the types of metabolites analyzed depend on the analysis coverage of the analysis platform and that most analyzed metabolites are high-abundance compounds, making low-abundance metabolites easy to overlook.
In contrast, targeted metabolomics only measures known metabolites with specific chemical structures or biochemical markers. Quantitative or semi-quantitative molecular metabolites can be determined using standard samples. This method takes advantage of a comprehensive understanding of a large number of metabolic enzymes, their kinetics, final products, and known biochemical pathways. By using targeted metabolomics, sample preparation can be optimized to reduce the advantage of high-abundance metabolites in the analysis. Abnormal correlations in metabolic products may be discovered by analyzing multiple known metabolites under specific physiological conditions.
Targeted metabolomics is commonly used in the study of amino acid metabolomics, carbohydrate metabolomics, and lipid metabolomics. Compared with non-targeted metabolomics, it is more targeted and can provide absolute quantification of target metabolites.
Plant hormone detection and metabolomics analysis are the two most commonly used techniques in the field of plant growth and development and stress research. The applications of these two techniques are often complementary. On the one hand, metabolomics is the most effective means of analyzing the mechanism of plant hormone action. On the other hand, the results of the analysis of growth, development, and stress processes using metabolomics often suggest the critical regulatory role of plant hormones in these processes. Therefore, the determination and metabolomics analysis of plant hormones are often used together in the study of plant growth, development, and stress.
Through the combined analysis of plant hormones and multi-omics, it was discovered that plant damage can induce the expression of defensive plant hormones and genes and proteins related to their synthesis, as well as a high expression of other genes, proteins, and metabolites related to defense, while inhibiting growth-related processes. Compared to mechanical damage, the systemic changes caused by insect oral secretions are more severe and long-lasting.