Differential Gene Expression Between Rice Hybrid And Their Parents And In Search Of Molecular Basis Of Heterosis

Differential expressed genes between hybrids and their parents obtained using differential expression technique is a hot spot on the explanation of the mechanism of heterosis. In this study, differential gene expression among hybrids FI and parents of one high heterotic cross combination (SH25/1R24) and one low heterotic cross combination(SH34/IR34) was conducted, in which the parent SH25 and SH34 were derived from a set of introgression lines carrying variant introgressed segments from Japonica cultivar Asominori in the background of Indica cultivar IR24. Yield and its components evaluation on the high heterotic cross combination and the low heterotic cross combination showed that the heterosis of F1SH25 mainly resulted from the increase of panicle number and filled grains per panicle, and that the hybrid breakdown of F1SH34 was mainly due to the decrease of filled grains per panicle, indicating that filled grains per panicle was the critical factor among factors contributing to yield heterosis. Further analysis of panicle-related traits showed that the increase of filled grains per panicle in the hybrid of F1SH25 was mainly due to the increase of the number of secondary rachis branches and grains in secondary rachis branches, and that the hybrid breakdown of F1SH34 was the combined effects of the number of primary and secondary rachis branches and grains in them, in which the decrease of the number of secondary rachis branches and grains in them was main.Using hybrids F1SH25 and F1SH34 and their parents SH25, SH34 and IR24 as materials, differential gene expression patterns during the panicle development were analyzed by cDNA-AFLP technique. For the genetic difference among materials was little, only 35 differential fragments were obtained. The expression pattern of genes differentially expressed between hybrids and their parents can be divided into four categories, (1 )bands observed in both parents but not in the F1, (2) bands occurring in only one parent but not in the FI or the other parent, (3) bands detected only in the F1 but neither of the parents and (4) bands present in one parent and F1 absent in the other parent. The results indicated that there was no certain relationship between differential gene expression patterns and heterosis.Of 35 differential expressed fragments, 8 fragments were cloned, sequenced, landed on chromosomes and analyzed functionally, respectively. Of 8 fragments landed on chromosomes,"two fragments were located on introgressed segments. Especially, one differential expressed fragment in the hybrid of high heterotic cross combination was located on the heterotic locus controlling the heterosis of grains per panicle. In other words, differential expressed genes in the hybrid of high heterotic cross combination were consistent with the analysis of heterotic locus mapping. One fragment only detected in the hybrid and parents of the low heterotic cross combination was 85% homologous to a gene in TCA.A differential fragment(DS19) was specifically detected in F1SH25, and the fragment homologous to DS19 was located on 19.6 cM form the distal end of chromosome 4, which was consistent with the heterosis locus controlling filled grains per panicle detected in our previous study. In this study, we first combined the differential gene expression, genotypes of parents, heterotic locus and heterosis phenotype, which provided a base for constructing a technique flat from phenotype, genotype, QTL mapping, the expression of heterosis-related genes to the explanation of the molecular basis of heterosis.