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Review
, 5 (12), e02952
eCollection

Regulation of L-proline Biosynthesis, Signal Transduction, Transport, Accumulation and Its Vital Role in Plants During Variable Environmental Conditions

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Review

Regulation of L-proline Biosynthesis, Signal Transduction, Transport, Accumulation and Its Vital Role in Plants During Variable Environmental Conditions

Mukesh Meena et al. Heliyon.

Abstract

Background: In response to various environmental stresses, many plant species synthesize L-proline in the cytosol and accumulates in the chloroplasts. L-Proline accumulation in plants is a well-recognized physiological reaction to osmotic stress prompted by salinity, drought and other abiotic stresses. L-Proline plays several protective functions such as osmoprotectant, stabilizing cellular structures, enzymes, and scavenging reactive oxygen species (ROS), and keeps up redox balance in adverse situations. In addition, ample-studied osmoprotective capacity, L-proline has been also ensnared in the regulation of plant improvement, including flowering, pollen, embryo, and leaf enlargement.

Scope and conclusions: Albeit, ample is now well-known about L-proline metabolism, but certain characteristics of its biological roles are still indistinct. In the present review, we discuss the L-proline accumulation, metabolism, signaling, transport and regulation in the plants. We also discuss the effects of exogenous L-proline during different environmental conditions. L-Proline biosynthesis and catabolism are controlled by several cellular mechanisms, of which we identify only very fewer mechanisms. So, in the future, there is a requirement to identify such types of cellular mechanisms.

Keywords: Biochemistry; Cell biology; Cellular mechanisms; Environmental stresses; L-proline; Molecular biology; Osmoprotectant; Plant biology; Signal transduction.

Figures

Figure 1
Figure 1
Figure showing the metabolic pathway of L-proline through glutamate and ornithine. It also indicates the basic difference between the glutamate pathway and ornithine pathway for L-proline synthesis.
Figure 2
Figure 2
Role of L-proline in plant growth and stress tolerance. L-proline plays important role as an osmolyte (protective purpose) and responsible to maintain the redox equilibrium through control the ROS and MG, increases photosynthetic production, can adjust development and metabolic signaling networks monitoring mitochondrial roles, stress utility and development (reformed from Szabados and Savouré, 2010).
Figure 3
Figure 3
Schematic presentation of the ornithine pathway during L-proline synthesis which occurs in mitochondria and cytoplasm/chloroplast. Synthesis of L-proline occurs in the cytosol as well as in the chloroplast, while L-proline degradation is implemented in the mitochondrion.
Figure 4
Figure 4
Figure showing the regulation of L-proline metabolism during the course of phosphate starvation (Pi) and osmotic stressed conditions. During the course of osmotic stress, L-proline accumulation occurs and structured by the stimulation of P5CS1 and suppression of PDH1 genes, correspondingly. Activation of P5CS1 gene is regulated by ABA signals, probably completed by the ABRE cis acting motif in the promoter. Phosphate starvation stimulated PHR1 and PHL1, which induces by P5CS1 via binding to its P1BS motif. Similarly, PDH2 is also stimulates by PHR1 and PHL1 and Pi scarcity. During phosphate starvation, NCED3 also induced which can increase ABA levels. ABA signals control plant growth and activates several stress-associated genes, comprising PHL1 and P5CS1.
Figure 5
Figure 5
Flow diagram showing the signaling pathway for L-proline activation under leaf senescence.
Figure 6
Figure 6
Hypothetical model showing L-proline mediated high temperature tolerance in plants (Adopted from Rai et al., 2018).

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