Progress in the functional study of phospholipases and their hydrolysis products

Recently, invited by Progress in Lipid Research, our rape team published a review entitled "The functions of phospholipases and their hydrolysis products in plant growth, The functions of phospholipases and their hydrolysis products in plant growth, development and stress responses". The review systematically introduced the protein structure, substrate specificity, enzymatic reaction conditions and mechanism of action of the plant phospholipase family, and discussed the role and significance of each phospholipase in plant growth, development and stress responses.

Phospholipids are the basic components of cell membranes, which are the starting location for organisms to perceive environmental stimuli. Their hydrolysis produces various lipid molecules, such as free fatty acids (FFA), phosphatidic acid (PA), diacylglycerol (DAG), lysophospholipids and soluble head groups. Numerous studies have shown that these lipid molecules play an important role in plant growth, development and response to adversity. Plant phospholipases catalyze the hydrolysis of cell membrane phospholipids and can be classified into phospholipase A (PLA), phospholipase C (PLC) and phospholipase D (PLD) depending on their hydrolysis sites. PLA cleaves the sn-1 and/or sn-2 sites of glycerophospholipids to release free fatty acids and lysophospholipids. PLC hydrolyzes the phosphodiester bond close to the glycerol side to produce DAG and phosphorylated head groups, while PLC hydrolyzes the phosphodiester bond near the glycerol side to produce DAG and the phosphorylated head group, while PLD hydrolyzes the phosphodiester bond near the head group side to produce PA and the head group.

This review provides a comprehensive overview of the research progress related to the plant phospholipase family, which is subdivided into different subfamilies based on PLA, PLC and PLD protein sequences, conserved structural domains, mechanism of action, substrate specificity and enzymatic activity reaction requirements, and their physiological functions. Arabidopsis PLA is divided into three subfamilies: pPLAӀ, pPLAӀӀ and pPLAӀӀӀ. PLC is divided into non-specific PLC (NPC) and phosphatidylinositol specific PLC (PI -PLC), and PLD is divided into six subfamilies PLDα, β, γ, δ, ε and ζ. Different phospholipases play multiple roles in various cellular processes in plants, such as the activation of pPLAs leading to the production of free fatty acids and lysophospholipids. Under environmental stress conditions (e.g., drought), pPLAs can regulate the morphology of plant organs, such as lateral root number, leaf thickness, angiosperm length, seed size, etc., by regulating the content of lysophospholipids in membrane lipids. pPLAs and pPLAs belong to the PLC family, but they have different mechanisms and signaling pathways for regulating plant responses to external stress. NPC regulates plant growth and adaptation to various stresses mainly through the content of DAG, a product of hydrolysis of phospholipids, and ABA, which regulates stomatal opening in response to water deficit and salt stress, while PI-PLC regulates plant growth and adaptation to various stresses mainly through the content of IP3, a product of hydrolysis of phosphatidylinositol. Phosphatidylglycerol (PG), phosphatidylethanolamine (PE), and phosphatidylserine (PS) (Figure 1). Its product PA is an important signaling molecule that is involved in regulating various physiological and biochemical processes in plants. Recent studies have shown that ZmPLA1 and ZmPLD3 can induce haploid formation in maize and have important utilization in breeding, but the molecular mechanisms of haploid induction by these two phospholipases are not clear.

This review points out that although a large number of studies have shown that phospholipases are involved in processes related to the regulation of plant growth and development and stress response, there are still serious deficiencies in the resolution of their mechanisms of action, among others. A full understanding of the biochemical properties, spatial and temporal expression relationships, and translational relationships among lipid molecules of each phospholipase would be beneficial for the in-depth analysis of the biological functions of plant phospholipases and promote the application of phospholipase genes in crop breeding