The Hxk1 gene, 20S proteasome,the 19S regulatory unit

The plant vasculardevelopment gene (RPN9), Retinoblastoma-concerning gene (RBR), a plant root developmentgene and some genes in meristem, as Dt1 and ML1 have been characterized by VIGS. Theseresults give rise that VIGS is one of the most powerful method for the observation of geneswhose loss-of- function mutants induce embryonic and seedling death.Cellular metabolism and functionVIGS has been implied to study plant cellular functions and metabolic paths, suchas biotin, enzyme biosynthesis, and organic manifesto. Burton et al. and Held et al. used PVXand BSMV vectors, alternatively, to study the usage of Cellulose synthase (Cesar) 142,143.VIGS was also implied to show the genes used in the biosynthesis of capsaicinoids (AT3, Comet,pat, and KS), D-appose (UDP-D- appose/UDP-D- xylose synthase, and AXS1), flaming 146,histone, and major proteins in the RNA silencing pathway, such as Argonaute1- and Argonaut 4-like genes. In more analysis, genes involved in the regulating the functions of PCD have beennow identified using VIGS.For example, the mitochondrial-related hexokinase Hxk1 gene, 20S proteasome,the 19S regulatory unit of the 26S proteasome and a regulatory gene of PCD (CDC5). VIGS hasalso been developed to characterized cellular functions of genes used in chloroplasts andmitochondria bio genes, plastid biogenetics, peroxisome biogenesis, alkaloid biosynthesis,isoprenoid biosynthesis, ascorbic acid biosynthesis, sterol biosynthesis, and membranebiogenesis.Merits and demerits of VIGSAs comparing with other genomic methods, VIGS has many advantages:(i) VIGS is much faster. An important characteristic of VIGS is that it cancause loss-of- function expression of a specific gene in a short period oftime. Therefore, the gene functionality can be accessed quickly,obviating the tedious method of plant regeneration.(ii) (ii) Plant transformation is excluded, which means that studies of genefunctionality in plants that are more difficult to transfer (e.g., cottonand soybean) would be more productive once the VIGS system isdeveloped.(iii) (iii) VIGS allows the study of genes that are necessary for plant viability.VIGS can be induced at the seedling or early development stages, andhas been developed as a powerful tool in the observation of geneswhose mutations induce embryonic and seedling-death. VIGS is the onlymethod that allows the analysis of such plant genes that are used inplant development.(iv) (iv) The phenotype of multiple genes with functional reduction can besilenced together through VIGS using conserved domains. On the otherhand, a specific site can be used for VIGS if only one gene in a genefamily is projected to be silenced.(v) (v) It allows rapid comparison of the functions of same genes betweendifferent plant species simultaneously, developing more identical genefunction identification.VIGS also has some disadvantages or limitations. For example(i) In most cases, the phenotypes of gene cannot be completelyreduced through VIGS. As the expression of the target gene isretarded, the remaining phenotype of the target gene can besame for its function. Therefore, for those genes, the loss-of-function expression cannot be observed by VIGS.(ii) (ii) VIGS requires before knowledge of target gene sequenceinformation. The effectiveness of silencing may be compared byretarded genes, unless the full genome or sufficient ESTsequences are present.(iii) (iii) Genes give expression during germination or the earlyseedling stage cannot be observed by VIGS, because VIGS isusually shown on adult plants and most of the VIGS phenotypeis not transfer to next generation.(iv) (iv) The efficiency may differ and the expression of VIGS is notvery stable one. Results may not be same among differentexperiments or different plants. To get solution of this problem,it is common to use a marker gene that gives a visible silencingphenotype as a positive control.Conclusion and future of this VIGSOver the previous 15 years, VIGS has been successfully implied to give discovery andconfirm gene functions in many crop plants, including both dicotyledonous andmonocotyledonous crop plants. Furthermore understanding of the method of gene silencingand growth of vectors for VIGS will led to most plant species already studied by newly madeVIGS systems, especially those that are difficult to observe by conventional methods. Now,more plant genomes have been sequenced, and new molecular biology methods have beenestablished for VIGS.For example, artificial miRNA silencing vectors have been implemented inVIGS, and a VIGS cDNA library was made using the gateway system. With more technicalenhancements, VIGS will continuously to be frequently used in plant functional genomes.

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