Rice Genetics IV - IRRI books - International Rice Research Institute

Table 2. Growth performance of transgenic plants in soil under water-stress conditions.Rice line Major plasmid Fresh shoot wt a Fresh root wtcomponents (mg plant –1 ) (mg plant –1 )JS110 (L3) Act1-uidA 300 ± 20 (100) 90 ± 12 (100)JS102 (L1) Act1-p5cs 550 ± 60 (183) 130 ± 20 (144)JS112 (L5) AIPC-p5cs 940 ± 100 (310) 220 ± 30 (224)JS112 (L7) AIPC-p5cs 730 ± 70 (243) 170 ± 20 (189)aMean ± standard error represents the averages of 6 plants. Values in parentheses arethe percentages of p5cs-transgenic plants compared with control plants (L3), representedby 100. The spread of data within each set of 6 plants was rather small.Growth performance of transgenic rice plants under salt-stress conditions. Tocreate high soil salinity, 300 mM NaCl solution was added to the trays in which thepots were placed. We found that, similar to the results under water-stress conditions,AIPC-p5cs transgenic rice plants under salt-stress conditions grew better than Act1-p5cs plants. In conclusion, stress-inducible transgene expression in p5cs plants showssignificant advantages over constitutive expression of the p5cs transgene in the growthof rice plants under salt- and water-stress conditions (Cheng et al 2000).Effects of matrix attachment region sequences on transgene expressionTransformation of cereal crop plants has become a relatively routine procedure inmany laboratories. However, many unexpected and often undesirable findings havebeen observed in transgenic plants with respect to transgene expression. The morecommonly observed phenomena include transgene silencing and variations in theexpression levels of transgenes between individual transformants that are not correlatedwith copy number (Kumpatla et al 1998, Stam et al 1997). However, chromatinstructure appears to affect the level of gene expression by exposing or not exposingDNA sequences to the transcriptional machinery (Stam et al 1997).Matrix attachment regions (MARs), also known as scaffold attachment regions(SARs), are DNA sequences that bind to a cell’s proteinaceous nuclear matrices andare thought to form DNA loop domains. MAR sequences are thought to form theboundaries of transcriptionally active DNA loop domains, thereby blocking the influenceof neighboring sequences on gene expression. When a transgene flanked byMAR sequences is introduced into a cell, the transgene can presumably form an independentloop domain once it is integrated into the chromosome and thereby minimizeposition effects (Spiker and Thompson 1996). Different MAR sequences have beenshown to increase the levels of transgene expression (for a review, see Holmes-Davisand Comai 1998) and reduce variations in transgene expression between transformantsin dicotyledonous plants (Allen et al 2000, Mlynarova et al 1994). Transgene silencingin monocots is a widespread phenomenon and has been reviewed recently (Iyer etal 2000), but studies of the effects of MAR sequences on transgenic expression inmonocots are limited (Vain et al 1999).Transgenic approaches for generating rice . . . 429