Rice Genetics IV - IRRI books - International Rice Research Institute

Genetic and molecular basisof heterosis in riceQifa Zhang, Jinping Hua, Sibin Yu, Lizhong Xiong, and Caiguo XuWe have conducted a series of studies to elucidate the biological mechanismof heterosis using rice as the model system. We analyzed the geneticbasis of heterosis using an F 2:3population and an “immortalized” F 2populationderived from a cross between Zhenshan 97 and Minghui 63. Our resultsdemonstrated the involvement of large numbers of two-locus interactions, orepistasis, underlying the genetic basis of quantitative traits and heterosis.We assessed the relationship between gene expression and heterosis byassaying the patterns of differential gene expression in hybrids relative totheir parents in a diallel cross. The analysis revealed that differentially expressedfragments occurring in only one parent of the cross were positivelycorrelated with heterosis, and fragments detected in F 1s but not in the respectiveparents were negatively correlated with heterosis. For further analysis,384 fragments were recovered from gels and arrayed onto nylon membranes.Hybridization with RNAs from seedling and flag leaf tissues detectedan overall elevated level of gene expression in the hybrid compared with theparents. Several fragments showed much higher expression in the highlyheterotic hybrid than in other hybrids. Many of these fragments were sequencedand mapped to the rice linkage map, which provided insights intothe understanding. We believe that analyses combining genetic and molecularapproaches will eventually lead to the characterization of the biologicalmechanisms of heterosis.The use of heterosis has become one of the major strategies for increasing crop production.Hybrid varieties have contributed greatly worldwide to the production ofmany crop species, including the most important food crops such as maize and rice.There has also been considerable interest in the genetic basis of heterosis. Two hypotheses,the dominance hypothesis (Davenport 1908) and the overdominance hypothesis(East 1908, Shull 1908), were proposed early in the 20th century to explainthe genetic basis of heterosis. Although many investigators favored one hypothesisover the other, data allowing for critical assessments of the hypotheses remained largelyGenetic and molecular basis of heterosis in rice 173