| L-ascorbic acid (AsA), also named as vitamin C, which is the primary water-soluble antioxidant in plants and animals. In plants, AsA serves as a major redox buffer, a cofactor for many enzymes, and a regulator of cell division and growth, as well as in signal transduction. Given the importance of vitamin C for plant and animal health, increasing AsA content has been the goal of many studies to improve the nutritive value of plants and their stress tolerance. During the last decades, a lot of researches have been done to identify the molecular mechanisam of AsA synthesis and to modulate the content of AsA in model plants. Analysis of genetic trait of AsA and identification the differentially expressed genes related to AsA are beneficial to crop breeding for high AsA content in non-heading Chinese cabbage.The main results are as follows:1. Six generations (P1, P2, F1, B1, B2 and F2) were derived from parents of non-heading Chinese cabbage (Brassica campestris ssp. chinensis Makino),'Wutacai' (with high AsA content) and 'Erqing' (with low AsA content), and the mixed major gene plus polygene inheritance model was used to investigate the genetic trait of AsA. The results showed that the trait of AsA was controlled by one additive major gene plus additive-dominant polygene in the joint analysis of six generations. The result of 2011 in plastic tunnel showed that the additive effect was 13.15. Heritabilities of major genes in the B1, B2 and F2 populations were 54.38%,38.58% and 18.69%, respectively. Whlie those for polygenes in the B1, B2 and F2 populations were 24.69%?36.92% and 40.7%, respectively. The result of 2013 in open field showed that the additive effect was 6.04. Heritabilities of major genes in the B1, B2 and F2 populations were 1.88%,6.41% and 45.04%, respectively. While those for polygenes in the B1, B2 and F2 populations were 39.67%?16.57% and 16.91%, respectively. The results of two-year experiments indicated that environmental factors could play roles in inheritance of AsA in non-heading Chinese cabbage. Environmental conditions should also be considered in the breeding process.2. To investigate the genetic trait of chlorophyll contents in non-heading Chinese cabbage (Brassica campestris ssp. chinensis Makino), six generations (P1, P2, Fi, B1, B2 and F2) were derived from two cultivars of non-heading Chinese cabbage 'Wutacai' and 'Erqing'. The mixed major gene plus polygene inheritance model were used for genetic analysis. The results showed that the trait of chlorophyll content was controlled by one additive-dominant major gene plus additive-dominant-epitasis polygene. The result of 2011 in plastic tunnel showed that the additive effect of major genes was 9.59, and the dominant effect was 1.17. Heritabilities of major genes in the B1, B2 and F2 populations were 22.86%, 41.65% and 61.24%23.08%, respectively. Those of polygenes in the B1, B2 and F2 populations were 59.18%,36.08% and 24.3%, respectively. The result of 2013 in open field showed that the additive effect and dominant effect of major genes were 4.48 and 2.09, respectively. Heritabilities of major genes in the B1, B2 and F2 populations were 5.66%, 38.51% and 26.29%, respectively. Those of polygenes in the B1, B2 and F2 populations were 64.99%,22.93% and 52.08%, respectively. The results indicated that single directional selection or recurrent selection would be used during cultivars improvements of non-heading Chinese cabbage, and the marker assisted selection method should be taken for production of high chlorophyll content lines. Besides, environmental conditions should also be considered in the breeding process.3. The cDNA-AFLP method was utilized to indentify differentially expressed genes involved in ascorbic acid accumulation of non-heading Chinese cabbage, with the F2 population derived from two cultivars of 'Wutacai' and 'Erqing'. A total of 184 TDFs (transcripts-derived fragments) were eluted and sequenced successfully. Among them,86 TDFs were predicted with putative functions through BLAST at NCBI and Brassica Database. These genes represented TDFs were found to participat in different biological processes, including metabolism (11.8%), cell structure (0.89%), transcription (9.9%), protein synthsis (8.91%), disease and defence (8.91%), photosynthesis and energy (12.87%), transporter (6.93%), signal transduction (5.94%), and cell division (1.98%). The results are firstly reported the differential transcriptomic analysis related to accorbic acid content in non-heading Chinese cabbage, which would be useful for clarifying the molecular mechaniam of accorbic acid synthesis and accumulation and providing theoretical basis for high accorbic acid content breeding.4. Transcriptional levels of genes are significantly related to traits which the genes controlled. Quantitative RT- PCR analysis of 22 genes involved in ascorbic acid synthesis and recycling showed no distinct difference between 'Wutacai','Erqing' and the F2 population.20 TDFs with different functions were also selected to determine expression profiles among the non-heading Chinese cabbage cultivars with different ascorbic acid contents. The results indicated most of these genes displayed differential expression in cultivars with different ascorbic acid level. Among them, ERF070 showed significantly up-regulated in 'Wutacai' and the F2 plants with high ascorbic acid levels, which was 3.3-7.5 fold higher than that of 'Erqing' and the F2 plants with low ascorbic acid levels. This result implied that ERF070 could contribute to the diffenent contents of ascorbic acid in non-heading Chinese cabbage. |
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