Studies On Molecular Basis Of Brassica Crops Heterosis At Gene Expression Level

Heterosis, a widely existing biological phenomenon, has been successfully exploited on breeding of many plants and animals. Brassica crops is a kind of crops in which Heterosis was most successfully utilized in China. Being good for people, the efforts for exploring the mechanism of heterosis have lasted for one century. The scholars of China and world have done a lot of work about heterosis, they have made the progress of method and direction, and have put forward many theory. However, many aspects remain unknown. With the inbred line 'Aijiaohuang 97-3-2', 'Huangxinwu 003-27', 'Shanghaiqing 98-4-2' of Chinese cabbage-pak-choi (Brassica campestris L. ssp. chinensis Makino; syn. B. rapa L. ssp. chinensis), the inbred line 'Baimanjing 001-24' of turnip [B. campestris L. ssp. rapifera (Matzg.) Sinsk; syn. B. rapa L. ssp. rapifera], the inbred line 'Huangyacai 97-8-6' of Chinese cabbage-pe-tsai (B. campestris L. ssp. pekinensis Olsson; syn. B. rapa L. ssp. pekinensis) and 6 hybrids as experimental material. Based on differential gene expression, the molecular basis of heterosis was studied by using cDNA-AFLP and physiological method. The main results are as follow:(1) Rosette leaves stages were the best time of Brassica vegetable heterosis according to yield, quality, adversity resistance, physiological and molecular biology.(2) The relationship between differential gene expression patterns at rosette stage and heterosis of biologic yield component traits in the hybrids and their parents was analyzed by using cDNA-AFLP. Four types of differential gene expression patterns were detected between hybrids and their parents: UNF₁ bands were observed only in F₁ not in parents; ABF₁ bands were observed in both parents but not in F₁; UNP bands were observed only in one parent but not in F₁ and another parent; DMP bands were observed in one parent and F₁ not in another parent. Analysis results showed that ABF₁ was significantly correlated with heterosis in leaf number, UNP was significantly correlated with heterosis in height of plant. These results indicated that differential expressed genes might play an important role in heterosis.(3) To construct Transcriptome map using cDNA-AFLPs in F₂ population derived from the cross inbred line 'Aijiaohuang 97-3-2' and inbred line 'Baimanjing 001-24'. Using 42 couples cDNA-AFLP primers out of 256, we analysized the segregation and distribution of cDNA-AFLPs in parents and F₂ plants. A total of 113 cDNA-AFLPs marker loci were mapped to 16 linkage groups, covering 3045.2 cM with an average distance of 29.7 cM.(4) In F₂ plants, 96 QTLs affecting 9 main agronomic characters were identified using QTLmaper 2.0 software by transcriptome map. There were 14 QTLs affecting plant height in groupl, 2, 3, 5, 6, 9 and 15, additive by dominance epistatic effects of qPH-3-5 and qPH-5-1 was the most, to increase plant height 9.9 cm. There were 11 QTLs affecting number of leaves in groupl, 2, 6,11 and 15, dominance by additive epistatic effects of qNL-11-1 and qNL-1-31 was the most, to increase number of leaves 13.45. There were 9 QTLs affecting weight of plant in groupl, 2, 6 and 15, dominance effects of qWP-1-42 was the most, to increase weight of plant 138.52g. There were 10 QTLs affecting leaf length in groupl, 2, 4 and 15, dominance effects of qLL-2-6 was the most, to increase leaf length 6.32 cm. There were 11 QTLs affecting leaf width in groupl, 2, 5 and 11, dominance by additive epistatic effects of qLD-2-14 and qLD-10-1 was the most, to increase leaf width 4.36 cm. There were 10 QTLs affecting petiole length in groupl, 6, 7, 13 and 14, dominance effects of qPL-1-2 was the most, to increase petiole length 9.46 cm. There were 9 QTLs affecting petiole width in groupl, 2, 4, 5 and 12, dominance by additive epistatic effects of qPD-2-19 and qPD-12-1 was the most, to increase petiole width 2.25cm. There were 11 QTLs affecting plant diameter I in groupl, 2,4 and 11, dominance effects of qPD1-1-5 was the most, to increase plant diameter I 2.96cm. There were 11 QTLs affecting plant diameter II in gr...