Abstract
When plants conquered land, they developed specialized organs, tissues, and cells in order to survive in this new and harsh terrestrial environment. New cell polymers such as the hydrophobic lipid-based polyesters cutin, suberin, and sporopollenin were also developed for protection against water loss, radiation, and other potentially harmful abiotic factors. Cutin and waxes are the main components of the cuticle, which is the waterproof layer covering the epidermis of many aerial organs of land plants. Although the in vivo functions of the group of lipid binding proteins known as lipid transfer proteins (LTPs) are still rather unclear, there is accumulating evidence suggesting a role for LTPs in the transfer and deposition of monomers required for cuticle assembly. In this review, we first present an overview of the data connecting LTPs with cuticle synthesis. Furthermore, we propose liverworts and mosses as attractive model systems for revealing the specific function and activity of LTPs in the biosynthesis and evolution of the plant cuticle.
Highlights
When plants conquered land, they developed specialized organs, tissues, and cells in order to survive in this new and harsh terrestrial environment
Synthesis of lipid polymers and cuticular waxes require de novo synthesis of precursors followed by transfer of the precursors through the plasma membrane to the apoplastic compartment [6]
It seems to require that the largely hydrophobic cuticle monomers traffic through the hydrophilic polysaccharide wall to reach the site of cuticle assembly
Summary
Plants colonized land some 500 million years ago [1]. The evolution of molecular barriers formed from lipid-based polyesters was essential for the long-term success of land plants. The hydrophobic polymer precursors and wax compounds are delivered to the polymerization sites outside the cell wall This last step is probably the least understood in cuticle. LTPs could stimulate the diffusion or transport of lipid polymer and wax components to the sites of cuticle accumulation on the extracellular side of the plasma membrane [30], which for instance could be the surfaces of leaves, stems or pollen. In comparison to wild type, the Atltp1.4-mutant shows only minor differences in cuticular wax composition In this mutant there is a 30% increase in 18:2 dicarboxylic acid, which is a major cutin component. LTPs may facilitate the transport or diffusion of the hydrophobic cuticle monomers and waxes in the hydrophilic cell wall, such LTPs could be functionally classified as Transporter LTPs (Figure 2).
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