【摘要】 以结球白菜(BrassicarapaL.ssp.pekinensis)结球前期心叶为材料,构建了结球前期球叶cDNA文库,随机挑选克隆单向单次测序后,共得到1162条峰图良好和插入片段长度大于150bp的可用序列。BLASTX及BLASTN序列比对分析表明,94.8%(1102/1162)的表达序列标签(EST)可在蛋白质或核苷酸水平上找到同源类似物。同源性最大的蛋白质按物种来源分析后发现,大约77%的功能已知蛋白质来自拟南芥(Arabidopsisthaliana),另外还有60个EST与已发表的植物基因没有同源性,这一部分EST对于研究结球白菜独特的生理和形态发育途径以及开展基因组分子作图具有重要的意义。同源蛋白质按其功能进行分类表明,参与蛋白质合成过程的酶或蛋白质的EST数量最多,其次是参与能量代谢过程(包括光合作用)的EST序列。在核苷酸水平上,全部EST中只有51%的同源物来自拟南芥。对上述1162条EST进行片段重叠群分析(contiganalysis)共获得895个非冗余片段重叠群,其中723个仅由一个EST组成(即singletons),表明结球白菜结球过程中表达的基因种类繁多。大量EST的获得为进一步了解结球白菜结球机制及获取相关基因提供了重要的序列信息。更多还原

【Abstract】 A cDNA library was constructed from the heading leaf in the early headi ng stage of Chinese cabbage(Brassica rapa L. ssp. pekinensis ). By sequencing th e randomly selected clones, 1 363 sequences longer than 200 bp with better trace data were got. After removing the Poly (A) and the contamination sequences, 1 1 62 ESTs longer than 150 bp were obtained, out of which 1 102 shared significant similarity with known sequences in protein and nucleotide databases of NCBI afte r being analyzed using BLAST X and BLAST N programs. The functional assignment o f expressed sequence tags(ESTs) was done based on the method used in the Arabido psis thaliana sequencing project. About 77% of the putative protein sequences wi th known biological functions matched with those of A. thaliana deposited in the non-redundant database of NCBI. These data suggested that Chinese cabbage was c losely related to A. thaliana. This result was different from those reported in other Brassica species. At nucleotide level, 51% (592/1 162) of the ESTs were h omologous to those deposited when all the ESTs were searched against the est-oth ers database. In addition, 60 ESTs had no homology with any of the plant genes r eleased from the GenBank. These ESTs are very important for understanding the un ique process of Chinese cabbage development and developing its genetic mapping. Among the genes with assigned functions, the most abundant representatives were those involved in protein synthesis and energy metabolism. With the 1 162 ESTs, 895 non-redundant contigs were generated after aligned using the SeqmanⅡmodule of DNA Star software at the threshold of more than 80% homology over a minimum o f 40 base pairs. A total of 723 singletons were obtained containing only one EST sequence, indicating that such many kinds of genes were expressed in the headin g leaf of Chinese cabbage. An expression profile of Chinese cabbage heading leaf with the 1 162 ESTs was therefore, acquired in this work, and this would be ver y useful for uncovering the mechanism of the heading process which was the most obvious character of Chinese cabbage, and perhaps other related species, such as B. oleracea. We expected that this work would accelerate the finding and charac terization of the genes specifically expressed in the heading stage of Chinese c abbage.更多还原