| Mei (Prunus mume Sieb. et Zucc.) being one of the traditionally flowers in China, is of great importance to cultural and economic value. It is crucial for the development of mei industry to breed new varieties gathering multiple prominent traits. However, being a woody plant with a long juvenile period, the breeding process is greatly limited. Moreover, it is difficult to determine the prominent genes controlling ornamaental traits, due to a poor research foundation for genetic mechanism of woody plants. However, marker-assisted selection can greatly shorten the breeding period and improve the efficiency of breeding process, and it has been applied less in mei. In order to detect the genetic factors and candidate genes of flower color, flower shape, petal numbers and weeping trait of mei, the F1 hybrid population ’LiuBan’×’FenTaiChuiZhi’ was chosen as the experimental materials and large-scale genetic markers exploitation was conducted utilizing the SLAF-seq strategy. The high-density linkage map of mei was then constructed and QTL analyses were then carried out for important traits of mei. Since weeping trait was a unique ornamental trait of woody plants, fine-scale mapping of weeping trait was performed, which provided idea for fine-scale mapping of other important trait of woody plants. The main results of this study were summarized as following:(1) The ’LiuBan’×’FenTaiChuiZhi’ population with a 387 population size and fine-scale phenotypic separation was screened out as mapping population. SLAF-seq strategy was utilized for genomewide molecular marker development, and the final linkage map with 8 linkage groups contained 8,007 markers, a marker density that has, to our knowledge, never been reached for mei and even any other species of Prinus. The map was 155,062 cM in length with an average distance of 0.195 cM between adjacent markers. The number of markers on linkage group 2 is the largest with 1,722 markers and 263.84cM in length. Linkage goup 6 is the shortest which contains 698 markers and 142.48cM in length. The average integrity of the SLAF markers in the Fl mapping polulation was 96%.(2) Utilizing the linkage map constructed, QTL anslyses were conducted for 15 groups of growth, plant architecture, flower related quantitative traits applying composite interval mapping strategy. In total,66 QTL were detected, with 58 candidate gens were screened utilizing the annotation database of mei genome.(3) Cellular structure, wood components and hormone level of juvenile branchs of weeping and upright mei were compared. The cell arrangement and lignified degree were different between upper and down side of weeping branches and upright branches. Besides, absence of amyloplast of gravity sensor was observed in weeping branches; The ligin content in upper side was lower than down side of branches of upright mei, with the ligin content in upper side was higher than down side in branches of weeping mei, and the branches of weeping mei was normal at the early growth stage according to the field observation.It was suggested that the formation of weeping trait was associated with lignification process of branches; Hormone level in weeping and upright mei at 5 developmental stages of branches were measured applying liquid mass spectrometry strategy, and it was speculated that ABA and GA3 maybe associated with weeping trait.(4) Inherited mode analyses of weeping trait of mei indicated that weeping shape in mei is a recessive monogenie trait with one or more modifiers to account for a deficiency of weeping seedlings. On this basis, weeping shape of mei was fine located within 10.54Mb-11.68Mb on linkage group 7 of mei by applying R/QTL analysis, Mutmap strategy and single marker analysis.18 candidates were considered as the most plausible genes of weeping in the casual region utilizing the annotation database of mei genome and results of former physiological test.9 candidate genes were obviously associated with formation and development of cell wall and synthesis and degradation of cellulose. Another 9 genes were predicted to be related to transcriptional regulation.The annotation results also confirm that the location of the locus affecting weeping is relative accurate.This high-quality and high-density genetic map is certain to assist in fine mapping and map-based cloning of important ornamental traits, which will also accelerate the molecular breeding for perennial woody plants in Prunus. QTL analyses results of the 15 crucial traits of mei will also facilitate molecular breeding of these complex traits. The fine mapping of weeping trait will also lay a solid foundation for mining genes controlling weeping trait, and provide a research strategy for localization of other important traits for woody plants. |
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