Rice Genetics IV - IRRI books - International Rice Research Institute

Correlation between gene expression in leaves and heterosisEight commonly used parental lines of hybrid rice were employed in this study includingthree restorer lines (Ce 64-7, Minghui 63, and Teqing) and maintainers offive male sterile lines (Guang B, Maxie, Qing Si Ai, Xian Gai, and Zhenshan 97).These lines were intermated in all possible nonreciprocal combinations to form adiallel set of 28 crosses, which were previously examined for yield and several agronomiccharacters in replicated field trials. This is the same diallel set of parents andhybrids that Zhang et al (1994, 1995) used to assess the relationship between geneticdiversity of molecular markers and heterosis.Differential display (Liang and Pardee 1992) of the mRNA was conducted usingflag leaf tissue from each of the parents and hybrids. The details of the analysis weredescribed previously (Xiong et al 1998). Six of the most informative primer combinations,displaying the largest number of differential bands, were used to survey thelevel of differential expression among the various crosses of the diallel set. Among atotal of approximately 350 bands that could be repeatedly amplified using the sixprimer pairs, 135 fragments represented sequences that were differentially expressedamong the parents and F 1 s in at least one cross. The analysis revealed several patternsof differential expression including (1) bands present in one parent and F 1 but absentin the other parent (DMPT), (2) bands observed in both parents but not in the F 1(ABF 1 ), (3) bands occurring in only one parent but not in the F 1 or the other parent(UNP), and (4) bands detected only in the F 1 but in neither of the parents (UNF 1 ).Both banding patterns of ABF 1 and UNF 1 signified the uniqueness of the F 1 comparedwith the parents (DF 1 ).We calculated the correlations of the various banding patterns with the performanceand heterosis of the hybrids (Table 5). In general, the correlation betweendifferential expression and hybrid performance is low. However, two types of differentialexpression showed highly significant correlations with heterosis: UNF 1 wasnegatively correlated with the heterosis of all traits, whereas UNP was positivelycorrelated with heterosis.We also calculated the correlation between differential gene expression and molecularmarker heterozygosity (Table 6). UNF 1 was correlated with general heterozygositythat referred to the overall level of heterozygosity of the hybrid (Zhang et al1994), and was negatively correlated with the specific heterozygosity of all six traitsTable 5. Correlations of various patterns of differential expression with heterosis of six traits(adapted from Xiong et al 1998).PopulationPlantTillers Grains Grainheight a Biomassplant –1 panicle –1 weightYieldABF 10.255 0.307 0.070 0.375 0.271 0.362UNF 1–0.454* –0.538** –0.449* –0.429* –0.517** –0.547**DF 1–0.197 –0.229 –0.360 –0.065 –0.242 –0.187DMP T–0.144 –0.128 –0.041 –0.153 –0.208 –0.135UNP 0.437* 0.486** 0.370 0.288 0.577** 0.377a*, ** = statistically significant at the 0.05 and 0.01 probability levels, respectively.Genetic and molecular basis of heterosis in rice 181