Maize Quantitative Genetic Studies Of Yield And Agronomic Traits And Gene Differential Expression Induced By Aluminum Stress

Maize was one of the most important food and feed crops with important economic significance, and the utilization of maize heterosis was one of the most successful examples in crops. The genetic characteristics and heterosis mechanism of maize yield and agronomic traits have been paid attention to extensively for many years. In this research, using a F_2:3 population from Yuyu 22 (zong3×87-1), a molecular marker linkage map was constructed and a two-location field experiment was conducted to study genetic characteristics and genetic basis of heterosis for important traits. Aluminum toxicity was the most limited factor in acid soil influencing maize production, and genetic improvement of maize aluminum tolerance was the main approach to increase the productivity under acid soil, but the mechanisms of maize aluminum tolerance were still unclear. As an other part of this research, two maize inbred lines were selected in which Mol7 was aluminum-sensitive and TL94B was aluminum-tolerant, and SSH method was adopted to construct SSH-cDNA libraries to study the gene differential expression induced by aluminum stress. The results were as following:1. The analysis of hereditary characters and heterosis of eight yield traits indicated that in F₁ generation and F_2:3 families, kernel weight per ear, kernel per row, ear length, row numbers and ear diameter performed higher heterosis in order, but the heterosis of rate of kernel production and weight of 100-kernel were very weak. Heterosis was significantly positive correlated with CV (coefficient of variation).2. According to correlation analysis, single-plant yield was significantly correlated with ear diameter, kernels per row, weight of 100-kernel, rate of kernel production and ear length orderly. Ear length was significantly negative correlation with ear diameter, and was significantly positive correlative with kernels per row and bare tip length. As three yield components, row numbers, kernels per row and weight of 100-kernel were significantly negative correlative with each other. Principal component analysis indicated that kernels per row, ear diameter, row numbers, ear length, bare tip length and weight of 100-kernel orderly was the principal factor influencing single-plant yield. Regarding to Yuyu 22, contributions of kernels per row and ear diameter to single-plant yield were increased, and that of ear length were decreased slightly but still important.3. The investigation of five agronomic traits showed that ear height and tassel branch number had higher broad heredity, but stalk diameter, days to pollen and days tosilk were lower relatively. Correlation analysis indicated that ear height, tassel branch number and stalk diameter were significantly positive correlative with single-plant yield, days to pollen and days to silk were highly positive correlative with each other, and tassel branch number was significantly positive correlative with stalk diameter too.4. Based on our genetic linkage map, combined data of field test and molecular markers, the QTLs of five agronomic traits were localized. As the results: seven QTLs of ear height, nine QTLs of tassel branch number, eight QTLs of stalk diameter, nine QTLs of days to pollen, and seven QTLs of days to silk were mapped, respectively. The results showed that all of these QTLs distributed uneven on chromosomes and had the trend to cluster together, indicating that the phenotype correlations of quantitative traits were resulted from correlations of the QTLs controlling different traits.5. Using SSH method, forward and reverse SSH-cDNA libraries were constructed for aluminum-sensitive Mol7 and aluminum-tolerant TL94B respectively. The insertion fragments of libraries were ranged from 250bp to 1.0kb, and its average length was about 550bp. Through differential hybridization, 124 positive clones were screened from Mol7-F library, 47 positive clones were screened from Mol7-R library, 103 positive clones from TL94B-F library, and 64 positive clones from TL94B-R library.6. Sequencing and analyzing these positive clones screened from four SSH-cDNA libraries, 232 kinds of ESTs were obtained totally among which 70.2% had significant homology with known genes, including 6.0% related to basic metabolism, 8.2% related to energy metabolism, 5.2% related to protein synthesis, 7.3% related to protein processing and destination, 12.5% related to transcription and regulation, 7.8% related to signal transduction, 7.9% related to transportation of substance, 9.9% related to disease and defense response; the remaining 29.8% ESTs were unknown about its functions, including 21 new-found ESTs.7. Reverse Northern hybridization method was adopted to screen ESTs related to aluminum tolerance, as a result, 16 candidate ESTs were acquired. Northern hybridizations were conducted for ESTs of NAD-dependent isocitrate dehydregenase gene, GDP dissociation inhibitor protein gene, cell division protein FtsH-like protease gene, pyruvate dehydrogenase El beta subunit gene, SNF2 domain protein gene, and plastidic glucose 6-phosphate dehydrogenase gene, and their differential expression characteristics were compared between Mol7 and TL94B.8. Using RACE method, the full-length cDNA sequence of maize NAD-dependent isocitrate dehydrogenase gene covering 1117bp was got, its coding regions was 765bp coding 255 amino acids. The multiple sequence alignment was conducted to compare the difference and similarity of sequence among maize, arabidopsis,brassica, tobacco and tomato. Through in silico cloning strategy, the candidate cDNA sequence of maize GDP dissociation inhibitor gene was obtained, it covered 1812bp in which coding sequence was 1239bp and coded 413 amino acids.9. In this research, 11 ESTs related to glycolysis and TCA cycle were obtained, including up-regulated pyruvate kinase, pyruvate dehydrogenase El beta subunit, pyruvate decarboxylase and NAD-dependent isocitrate dehydrogenase, and down-regulated glyoxylate pathway regulator gene. The information of these ESTs provided abundant molecular evidences and reasonable explanation of metabolism pathways to the secretion of organic acid induced by aluminum stress in gene expression level. 15 ESTs related to cell signal transduction were acquired in this research, analyzing the internal relationships of signal transduction systems, it indicated that the signal transduction of aluminum stress was related to MAPK signal pathway, calmodulin signal pathway and PI (phospholipid inositol) signal pathway, and three kinds of phytohormone including auxin, ABA, and ethene also involved in the responding and trunsducting of aluminum stress signals.10. Through analyzing the expression characteristics of important candidate ESTs of aluminum tolerance, it showed that TL94B had faster and stronger responding to aluminum stress than Mol7, and it was benefited to protect cells from aluminum toxicity and to possess better aluminum tolerance. From these results, it deduced that the diversity of maize aluminum tolerance was related to responding speed and intensity of different genotypes to aluminum stress.