what is the main function of cuticle in plants

<>stream The polymeric structure of cutin is not well understood. A summary of the interaction of environmental factors and regulatory genes that are known to influence cutin or wax biosynthesis is shown. Given the broad scope and space limitation, not every aspect of cuticle biosynthesis is covered in depth, and recent specialized reviews focusing on cuticle biomechanical properties (Domínguez et al., 2011), defensive functions (Reina-Pinto and Yephremov, 2009), and transport barrier properties (Burghardt and Riederer, 2006) may be of further interest. A cuticle /ˈkjuːtɪkəl/, or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Gregory Buda, Christiane Nawrath, and Lacey Samuels for generously providing microscopy images and Eric Fich, Laetitia Martin, and Dr. Iben Sørensen for helpful comments and discussion. Experiments further addressing this hypothesis will be particularly interesting, given the surprising finding that the cer9 mutant actually exhibits enhanced drought tolerance and water use efficiency (Lü et al., 2012). In plants, this is the outermost part that is secreted by the epidermis. 3A). uuid:12d0f488-1dd2-11b2-0a00-aa00689beaff In Arabidopsis, 21 genes are predicted to encode β-ketoacyl-CoA synthase, and for wax biosynthesis, the most important gene, based on the mutant phenotype, is CER6 (Fiebig et al., 2000). For example, studies of three tomato mutants (cd1–cd3), each of which has a greater than 95% reduction in fruit cutin levels, revealed only minor increases in the rate of water loss, and even among the mutants there was no clear correlation between cutin amount and susceptibility to desiccation (Isaacson et al., 2009). C. It protects the plant from predators. The cuticle is a waxy, water-repellent layer that covers all of the above-ground areas of a plant. The cuticles of plants function as permeability barriers for water and water-soluble materials. These authors also demonstrated that these transcription factors directly activate promoters of several cutin biosynthetic genes, further supporting a primary role in cutin regulation with a downstream effect on wax biosynthesis (Shi et al., 2011). The plant cuticle presents a physical barrier to pathogens that do not otherwise enter the plant by way of the stomata, wounds, or vectors. In some species, various lipophilic secondary metabolites, such as pentacyclic triterpenoids, flavonoids, and tocopherols, can also be substantial components (Jetter et al., 2006). It contains … However, the most critical adaptive trait for survival during terrestrialization would have been the ability to retain water in increasingly dehydrating habitats. Phylogenetic analysis of CD1 and homologous genes indicates that despite belonging to a very large gene family, the subfamily of GDSLs represented by CD1 is relatively small and well conserved, with sequences represented across diverse taxa of land plants (Volokita et al., 2011). 2013-08-21T19:09:18+05:30 If so, which enzymes are involved in this process? endobj H��WMs�F��W�HT�4fr��R\&�6��$T h��=��?_��x�z��Q��F��ū��a��\�/��|�bOc��|4_��4όcq�3I��J�(��43Ǝ��]4I�T��m4I��O�h��/t��j�F�eG�_��}1�ѫ�:"X��(^E�4��4�V5��j�H�&m)?��@J�uOZ��ذ"�)w�C��6�T"�ပ��å*|�K"W �"�M0�k�p? In contrast to the lack of association with cutin, extensive removal of wax from tomato fruit, accomplished by brief immersion of the fruit in an organic solvent, indicates that waxes contribute approximately 95% of the cuticle-mediated resistance to water diffusion, at least in tomato fruit (Leide et al., 2007). The Arabidopsis enzyme responsible for this is WSD1, an enzyme of the wax synthase/diacylglycerol acyltransferase family (Li et al., 2008). CER7 encodes an exosomal exoribonuclease, and the cer7 mutant exhibits reductions in stem wax and transcription of CER3, a major wax biosynthetic enzyme (Hooker et al., 2007). The cuticle is a multi-layer structure composed primarily of cutin, cutan, polysaccharides, lipids and waxes. Here, we summarize this pathway based on recent molecular genetic and biochemical studies using Arabidopsis and tomato (Solanum lycopersicum). 50 0 obj The IRG1 gene was found to encode a C2H2 zinc finger transcription factor that had previously been identified as a regulator of dissected leaf morphology (Chen et al., 2010). They may be found singly or less frequently in groups. In parallel, the past decade has seen considerable progress in understanding the biosynthesis of the major cuticle components and the complex regulatory networks that control cuticle synthesis and assembly. Recent progress in this area was achieved by studying the tomato mutant cutin deficient1 (cd1) and transgenic tomato plants in which CD1 expression was suppressed using an RNA interference strategy (Girard et al., 2012; Yeats et al., 2012b). In Arabidopsis, CER5/ABCG12 (Pighin et al., 2004) and ABCG11 (Bird et al., 2007) are required for wax export. This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. The Cuticle and the Stomata. Function of Leaf. However, the mechanism of plant perception of free cutin monomers is currently unknown (Boller and Felix, 2009). However, without it the fruit would never have existed in the first place. These proteins represent a unique class of LTPs, a family of small and typically soluble proteins that bind a variety of lipid substrates in vitro (Yeats and Rose, 2008). Another regulatory factor was identified through characterization of the rice CURLY FLAG LEAF1 (CFL1) gene, which encodes a WW domain-containing protein that negatively regulates cuticle biosynthesis. Here, we review recent progress in the biochemistry and molecular biology of cuticle synthesis and function and highlight some of the major questions that will drive future research in this field. In tomato fruit, severely decreased cutin levels in three cd mutants was associated with increased susceptibility to infection by Botrytis cinerea surface inoculation and also to opportunistic microbes (Isaacson et al., 2009). While mechanical rupture may be sufficient for cuticle penetration, particularly of thinner cuticles (Tenberge, 2007), most fungal pathogens also secrete cutinases, a class of small, nonspecific esterases that hydrolyze the cutin polyester and release free cutin monomers (Longhi and Cambillau, 1999). [��i�8�:�p|:쎮�I3��*�/�E]@�� 1Y��c�q/�[ � �8��ޛTum��X Another example of an “orphan” cuticle-associated protein resulted from analysis of the Arabidopsis bodyguard (bdg) mutant, which exhibits a microscopically disorganized cuticle with increased permeability but significantly increased levels of wax and cutin (Kurdyukov et al., 2006a). Scanning electron microscopy can reveal the elaborate and diverse morphologies of epicuticular wax crystals (Fig. These epicuticular waxes can confer distinct macroscopic surface properties: epicuticular films are responsible for the glossy appearance common to many leaves and fruits, while epicuticular wax crystals account for the dull, glaucous appearance of broccoli (Brassica oleracea) leaves and Arabidopsis (Arabidopsis thaliana) stems. The identification of CD1 as the first known cutin synthase raises several questions about the specificity and generality of the reaction that it catalyzes. endobj However, all the ABC transporters that have been implicated in cuticle biosynthesis to date are members of the ABCG subfamily, which has been associated with the transport of lipids and hydrophobic compounds in other systems (Moitra et al., 2011). We thank Drs. © 2013 American Society of Plant Biologists. <>/ExtGState<>/Font<>/ProcSet[/PDF/Text]>>/Rotate 0/Thumb 91 0 R/Type/Page>> uuid:2167317e-6b3a-462e-8f52-c356321db248 Export of some wax compounds also appears to be facilitated by glycosylphosphatidylinositol (GPI)-anchored lipid-transfer proteins (LTPs), LTPG1 and LTPG2, which are bound to the extracellular side of the plasma membrane (Debono et al., 2009; Lee et al., 2009; Kim et al., 2012). However, it has evolved a number of secondary functions that are consistent with its place as the outermost layer of primary aerial organs: it forms a physical barrier that is the first line of defense against pests and pathogens; in many species, elaborate epicuticular crystals help to form a self-cleaning surface, preventing dust and other debris from blocking sunlight; in some cases, it can act to screen excessive UV light; finally, as a defining feature of the epidermis, it plays a central role in development by physically establishing organ boundaries. Waxes reflect both UV and visible light, but not necessarily to the same extent, and the reflectance of UV has been reported to be greater in some cases (Holmes and Keiller, 2002). C, Transmission electron micrograph image of an Arabidopsis stem epidermal cell wall and cuticle. This highlights the competing selective pressures to generate and breach cuticle barriers at the frontier of the plant surface (Chassot and Metraux, 2005).