Sources of small peptides and their mechanisms of action in plant regulation
Based on the division of genomic origin, small peptides can be divided into two major categories:
One type is derived from small peptides in non-coding regions, and the other type is derived from products of protein-coding genes.Additionally, based on their intracellular distribution and localization, small peptides can be further classified into two major types: secretory small peptides and non-secretory small peptides.
Secretory peptide
Secreted small peptides function outside the cell, and their synthesis pathways are diverse. They can be exported to the outside of the cell through the conventional protein secretion pathway through the Golgi apparatus or trans-Golgi apparatus network, or directly from the endoplasmic reticulum through non-traditional pathways. or multivesicular body extrusion cells (Hu et al., 2021). Most of the small peptides identified so far are secreted. They are similar to conventional secreted proteins and carry a leader sequence at the N-terminus.
Secreted small peptides are further subdivided. One type is produced after undergoing a complex post-translational modification process, including tyrosine (Tyr) sulfation, proline (Pro) hydroxylation, and hydroxyproline (Hyp) glycosylation. chemical, etc., and then formed through large-scale proteolysis. These small peptides are called post-translationally modified small peptides. The other type is characterized by being rich in cysteine and the presence of multiple intramolecular disulfide bonds. Some of them have experienced the proteolytic process, and some have not experienced this process. They are collectively called cysteine-rich peptides.
Non-secreted peptide
Non-secreted small peptides are retained in cells due to their lack of N-terminal signal sequences. They include two types of functional peptides: one type is a transmembrane peptide that mediates intercellular communication and participates in the formation of membrane structure, and the other type is involved in signaling. Intracellular peptides that play a regulatory role in the conduction network (Xu et al., 2017). Nonetheless, under certain conditions, non-secreted small peptides may be released from cells and transmit signals between cells, especially in response to injury.
How small peptides act in plant regulatory networks
The mechanism of action of small plant peptides revealed in current research covers multiple levels, including inhibiting the translation of the main open reading frame (mORF), promoting miRNA function, participating in signal transduction, and interacting with target proteins.
Of particular concern is the role of small peptides in signal transduction. Small peptides serve as ligands that can trigger signal transduction events. Mature secreted small peptides will recognize and bind to specific receptors on nearby cell membranes (the receptors usually exist in the form of receptor-coreceptor complexes); some small peptides can even be transported over long distances (such as through dimensional tube binding system) and then bind to the corresponding receptor. In the small peptide-receptor mediated signaling model, the small peptide first binds to the extracellular part of the receptor complex, thereby activating its intracellular kinase domain (Kinase domain), and the receptor kinase then activates the downstream through phosphorylation. Signaling pathway components, such as MAPK cascades and transcription factors, achieve fine regulation of biological processes.
Absorption and utilization characteristics of small peptides
With their excellent bioavailability, small molecule peptides have shown unparalleled advantages in the uptake, transformation and utilization of nutrients. Their unique property of being able to cross the cell membrane intact and directly enter the cell interior highlights the high biological activity and effectiveness of small molecule peptides. In the absorption process, small molecule peptides avoid the degradation process of large molecular substances by digestive enzymes, achieving efficient absorption and transport.
The role of small molecule peptides in regulating enzyme function
Enzyme synthesis and activity activation: Small molecule peptides play a crucial role in the construction and regulation of enzyme systems. They not only participate in the synthesis process of enzyme molecules, but can also activate the potential activity of enzymes, doubling the efficiency of enzymes in the metabolic process of organisms. In addition, small molecule peptides also extend the life of the enzyme by stabilizing the molecular structure of the enzyme and ensuring that it continues to function normally.
Optimization of cell membrane permeability and enhancement of physiological functions: Small molecule peptides can significantly improve the permeability of the cell’s intermediate metabolic membrane. By optimizing the membrane structure and function, the cells’ selective absorption of nutrients and harmful substances are enhanced. excretion efficiency. At the same time, small molecule peptides can also strengthen the defense mechanism of cell membranes, effectively prevent the invasion of pathogenic microorganisms, and maintain the health and stability of cells.
The contribution in genetic information transmission
Small molecule peptides play an important role in the regulation of genetic information. By participating in the transcription process of DNA, they ensure the accurate translation and faithful transmission of cell genetic advantage information, thereby ensuring that cells always maintain their genetic advantages during the process of continuous renewal and differentiation.
Small molecule peptides have dual nourishing and repairing functions for cells
Small molecule peptides have dual effects of nourishing and improving functions of cells. On the one hand, they can promptly replenish the nutritional needs of cells and repair damaged or dysfunctional cell structures; on the other hand, small molecule peptides can promote the improvement and optimization of overall cell function by regulating the internal metabolism and physiological functional status of cells.
Application in plant stress resistance
Small molecule peptides also show strong application potential in the plant field. They can not only provide necessary nutritional supplements to plant cells and repair damage caused by stress, but also improve plants’ response to abiotic stresses (such as high temperature, high temperature, etc.) by optimizing plant physiological functions. drought, low temperature, low light, soil salinization, etc.), thus acting as an effective biological stress carrier and function regulating substance.