| Waxes form a continuous lipid membrance covering the epidermal cells of all aerial plant organs. It mainly comprised of long-chain aliphatic compounds derived from very long chain fatty acids that are enlonged from C16 or C18 long fatty acids in ER by many fatty acid elongation (FAE) complexs. The chemical and physical properties of cuticular waxes indicate that they have vital functions for plant life. The primary role of cuticular waxes is to restrict non-stomatal waterloss. Waxes also have many other functions, such as protection against UV radiation and resisting bacterial and fungal pathogenes.The synthesis and secretion pathway of the plant wax are conservative in all plants. First, the de novo synthesis of the saturated fatty acid to the C16 or C18 occurs in the plastid. Then the C16 or C18 saturated fatty acid are transported out of the plastid for the elongation to the very long chain fatty acid (VLCFAs). The derivatives are produced from VLCFAs on the endoplasmic reticulum (ER) catalysed by membrane-associated multienzyme complexes. Up to date, only several enzymes about the wax synthesis are separated and we can use them to predict the wax synthesis and secretion pathway. Not only in the plastid, but also on the ER, the fatty acid synthesis pathway is composed of a series of four-step reactions cycle: Condensation, reduction, dehydration and second reduction. The acyl chain will be added C2 unit from malonyl-CoA (ACP) every cycle. There are two pathways for the production of the fatty acid derivatives: the acyl reduction pathway to produce primary alcohols, esters and maybe aldehydes and the decarbonylation pathway to aldehydes, alkanes, secondary alcohols and ketones.The predominant cuticular wax constituents are all derived from saturated VLCFAs with predominant chain length C20–C32. Fatty acid elongation involves four enzymatic reactions, which are successively catalyzed by a KCS, a KCR, a h-hydroxyacyl-CoA dehydrase (DCH) and an ECR. KCS catalyses the condensation of malonyl-CoA with a long chain acyl-precursor. This is the rate-limiting step of VLCFAs synthesis which determines the acyl chain length of the VLCFAs produced . Four KCS have been studied from Arabidopsis. A single condensing enzyme, FAE1, catalyzes VLCFA synthesis in seeds, whereas KCS1 , FDH and CER6 , have been implicated in the synthesis of wax components.T. halophila, a close relative of A. thaliana, have similar heredity characteristics and growth habits with A. thaliana: small genome, short life cycle, self-fetilization, abundance seeds, and have several prominennces to A. thaliana: higher tolerance and more wax amounts, etc. All of these have revealed the potential of new genomics-based approaches with T. halophila to identify and clone valuable new genes conferring traits not apparent in A. thaliana, especially the genes involved in the biosynthesis of plant epicuticular wax.The traits of whole plant, crystallization patterns and chemical composition of leaf cuticular waxes of three ecotypes of T. halophila (ecotype Shandong, Yukon, Xinjiang), were examined. T. halophila leaf surfaces were glossy before flower initiation but glaucous after. There are few differences of glossy leaves among these three T. halophila. However, the heavy glaucousness, total wax amounts, wax crystal structures, and wax chemical constituents on inflorescence leaves differed significantly. Glaucousness resulted from the presence of densely distributed epicuticular wax crystals visible with electron microscopy. Glaucous leaves of both T. halophila ecoytpe Shandong and Xinjiang produced 1.9- and 1.8-fold more total wax, respectively, than leaves of ecoytpe Yukon. Glaucous leaves of T. halophila ecoytpe Shandong and Xinjiang had similar wax composition and wax crystallization patterns .Real-time quantitative PCR is a new technique with high sensitivity and high speed , which is applied to the research of gene expression analysis. The project have completed to analyze their expression model of 21 wax synthesis-related KCS gene in different periods of T. halophila ecoytpe Shandong by Real-time Quantitative PCR, and have gained some important experiment results. We showed that 61.9% of the 21 KCS genes had higher levels of expression in caulines leaves than in matrual rosette leaves (16w-rosette leaves), indicating that these genes have positive corelation with wax synthesis. However, 85% of the 21 genes showed similar expression profiles as in A. thaliana. We speculated that maybe the micro regulation of promotors or miRNAs, or DNA Methylation regulated the expression of these genes. We also measured the expression of the corresponding transcripts in cauline leaves of three T. halophila species. Our results showed that 47.6% KCS genes expressed to similar levels in the three samples. 33.3% KCS genes expressed to highest levels in T. halophila ecotype Shandong, and among them five expressed to camparable levels to ecotype Xinjiang.At1g07720, a gene belongs to FDH family, was known little in A. Thaliana up to date. We used a RNAi vector, pGSA1252, to specificly silence At1g07720 in T. halophila. The transgenic lines will be researched by Real-time Quantitative PCR.
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