Rice Genetics IV - IRRI books - International Rice Research Institute

Table 6. Correlations of various patterns of differential expression with general and specificheterozygosity for each of the six traits (adapted from Xiong et al 1998).Specific heterozygosityGeneralPopulation hetero- Plant Biomass Tillers Grains Grain Yieldzygosity a height plant –1 panicle –1 weightABF 10.196 0.195 0.243 0.294 0.156 0.125 0.170UNF 1–0.618** –0.509** –0.551** –0.508** –0.457* –0.427* –0.526**DF 1–0.404* –0.304 –0.300 –0.213 –0.289 –0.289 –0.341DMPT –0.149 –0.173 –0.195 –0.239 –0.040 0.049 –0.125UNP 0.191 0.520** 0.527** 0.006 0.440* –0.052 0.528**a*, ** statistically significant at the 0.05 and 0.01 probability levels, respectively.analyzed. In contrast, UNP was positively correlated with specific heterozygosity formost of the traits.Analysis of the differentially expressed fragmentsThe differentially expressed fragments were excised from the gels, reamplified with polymerasechain reaction, and cloned into plasmid vectors. A total of 384 clones were recoveredand arrayed onto nylon membranes. RNA samples were isolated from threeleafstage seedling and flag-leaf tissues of the hybrid Shanyou 63 and its two parents,Zhenshan 97 (male sterile line) and Minghui 63 (restorer). Probes were prepared fromthe RNA tissues by reverse transcription labeled with α- 32 P and hybridized with thenylon membranes. The intensity of the hybridization signal was scanned to determinethe level of expression of the cloned fragments in the respective tissues.Unlike the presence vs. absence type of difference revealed by differential display,the differences in hybridization signal among the clones were quantitative ratherthan qualitative. In flag-leaf tissue, a large number of clones (114) showed a higherexpression in Zhenshan 97 than in Minghui 63, whereas only a small number of clones(36) showed a higher expression in Minghui 63 than in Zhenshan 97 (Table 7). Thereverse was the case in the seedling tissue. Many more clones showed a higher expressionin the hybrid than in both parents in both tissues, with the possible exceptionof the comparison of Zhenshan 97 with the hybrid in flag-leaf tissue, in which approximatelythe same number of clones showed a higher expression in the hybrid asthe number showing a higher expression in Zhenshan 97. Thus, collectively, the hybridhad an obvious advantage in terms of the number of genes showing elevatedexpression compared with the parents.We further calculated the level of heterosis in gene expression, treating the readingof the signal intensity as a quantitative trait. At the seedling stage, a much largernumber of clones showed positive heterosis in expression than the number showingnegative heterosis. At the flag-leaf stage, a slightly larger number of clones showednegative heterosis than those showing positive heterosis (Table 8). Again, the hybridhad an advantage in the level of gene expression over the parents, especially at theseedling stage.182 Qifa Zhang et al