Maternal Control Of Seed Weight In Rapeseed(Brassica Napus L.)

As one of the three components of seed yield, seed weight of rapeseed(Brassica napus L.) natural germplasms showed ≈ 4-fold variation, which is invaluable for genetic improvement. However, the regulatory mechanism of the natural variation is poorly understood till now. In the current study, the morphological, cytological, genetic, physiological and molecular causes of the natural variation for seed weight were investigated. Especially, QTL analysis, differentially expressed gene analysis and validation for candidate gene at molecular level were investigated. In conclusion, our study has systematically demonstrated a new fashion of the maternal control of seed weight that the size of source organ(silique length rather than width) may affect that of sink organ(seed size rather than bulk density). The main research contents and conclusions in the study were as follows:1. Seed weight is determined by its size rather than bulk density; Meanwhile, cell number is more tightly correlated with final seed weight in B. napus.2. The maternal effect value was estimated to be 0.93, indicating that the weight of the F1 hybrid seeds was mainly controlled by the maternal parent(93%). There is little or no xenia and cytoplasmic effects for seed weight in B. napus.3. Firstly, we concluded that silique wall photosynthetic might highly associated with final seed weight. Secondly, physiological evidences indicated that difference in the silique size(length rather than width) might result in difference in silique wall(maternal tissue) photosynthetic area, carbohydrate gross and the final seed weight(size rather than bulk density).4. Three pleiotropic QTLs for seed weight and silique length were identified via linkage mapping. Of these, two were major QTLs which showed larger effects for both traits. The two major pleiotropic QTLs were validated and fine-mapped according to regional association mapping. We also concluded that silique length is an upstream determinant of seed weight and co-localized QTLs act indirectly on seed weight via their effects on silique length.5. Genome-wide gene expression analysis showed that genes related to development, signal transduction, transport in the silique wall, and seed development, cell division, nutrient reservoir and ribosomal protein in the seed were all up-regulated in large-seed bulk. In addition, several homologous genes(differentially expressed genes in B. napus) could influence silique length and seed weight in Arabidopsis at the same time.6. Combined QTL analysis, differentially expressed gene analysis, SNP and gene annotation, we screened two candidate genes for seed weight. The two candidate genes were confirmed as functional genes for seed weight. However, whether they are the source genes for target QTLs need further evidences.7. In conclusion, we proposed a new fashion of the maternal control of seed weight in rapeseed.8. Based on difference of DNA sequences, one marker for seed weight and silique length located on QTL region was developed, which could be applied for marker assisted breeding.The points of innovation in the research are as follows:1. The proposed general rule for seed weight will lead a solid theoretical foundation for following study.2. The system’s interpretation of maternal control mode for seed weight(the size of source organ may affect that of sink organ via maternal effect) will lead to a new area of exploration in seed weight research.3. Two candidate genes were confirmed as functional genes for seed weight. One molecular marker was developed for marker assisted breeding.