Rice Genetics IV - IRRI books - International Rice Research Institute

Fig. 4. X-gluc staining of germinating R 1 JDV95 seedlings. GUS activity, detectedby histochemical staining (Jefferson et al 1987), was absent for the first 36 h ofgermination, but was evident between 48 and 60 h and inactivated afterwards.The yellow bar represents 1.5 mm.sulted in reactivation of the gene at the single-copy locus (Table 2). This is reminiscentof paramutation where a paramutated locus regains expression when segregatedaway from a paramutagenic locus (Matzke et al 1996). Crosses between JDV92 andother functional locus-containing lines is being conducted to determine if its multigenelocus can silence other functional single transgene loci.To study the epistatic effects of silenced loci on functional loci, sexual crosseswere made. As observed for tobacco (Matzke et al 1993, 1994, Nap et al 1997, Neuhuberet al 1994, Schmulling and Rohrig 1995, Vaucheret 1993, 1994), different resultswere obtained for individual crosses. For example, there was no silencing when singlecopylines JDV85 or JDV86 were crossed to the silenced two-copy line JDV95, butwhen they were crossed to multicopy lines JDV83 or JDV90, GUS expression wassilenced in the resulting hybrid plants (Table 3). The differences in outcome mayGene silencing and its reactivation in transgenic rice 473