Fine-mapping and Phenotypic Characterization of a Major QTL for Root Development

• Main Authors: Sheng-Ming Chen, 陳晟銘
• Other Authors: Wei-Ming Leu
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/48156110792211380688

碩士 === 國立中興大學 === 生物科技學研究所 === 99 === Two rice lines, TNG67 and SA1613.1, usually produce 6~7 panicles each plant but their F2 progenies have wide segregations in panicle number and root biomass, indicate quantitative trait loci (QTL) involved in this trait. Primary mapping on a F2 population revealed two major QTL, qPN1 and qPN11, each with ~22% phenotypic variation explained (PVE). When both qPN1 alleles are from TNG67, allele of qPN11 from SA1613.1 acts dominantly to produce rootless plant with tiny single tiller, abbreviated as “rolts”. To characterize effect of the qPN11 allele independently, and to construct materials for its fine-mapping, a Near-Isogenic Line (NIL) was supposed to be established by backcrossing. However, the tiny single tiller phenotype for such a NIL hindered this process. A Backcrossed Recombinant Inbreed Line (BRIL) which heterozygous on both qPN1 and qPN11 but mostly homozygous as TNG67 throughout the genome was therefore established instead. Marker-assisted selections (MAS) were employed during the breeding process. Finally, using 146 BC2F5 segregating progenies from the selected BC2F4 BRIL line, candidate genes for qPN11 was narrowed down to a 2 Mb region, most likely reside between two InDel markers, I32635-4 and D32674, which is 300 kb apart. To characterize phenotypic defects of rolts, BC2F5 segregating seedlings were screened by markers that associated with qPN1 and qPN11. Hydroponic culture of rolts seedlings revealed an early symptom on 5 DAG, showing short seminal root, very few lateral root and absence of adventitious root. Noticeably, formation of tiller but not adventitious root resumed if rolts seedlings were remained within hydroponic culture, indicates that no major defect for its tiller development. Moreover, node seems to be formed normally in rolts plant as its node number reached ~15 in mature plants, although very tiny. Cryo scanning electron microscopic examination of 14 DAG seedlings revealed a similar radial structure between normal and rolts plants, suggesting that pattern formation and differentiation are not affected. Further confocal microscopic studies suggest that rolts plant is basically normal in cell size and organization, with thicker cell wall and more varied cell shape. However, no long cell can be found in the root elongation zone and almost all cell form root hair. Therefore, the major defect for rolts seems to be on cell elongation.