病原菌诱导转录的水稻Rim2家族转座酶编码亚组的结构与分布

Structure and Distribution of the Transposase-Coding Subgroup of the Rice Rim2 Family Transcriptionally Induced by Magnaporthe grisea

以基因组克隆Rim2 5 6 9为代表 ,分析了该家族中转座酶编码亚组的分子结构 ,同时对Rim2因子在染色体和不同水稻品种之间的差别分布情况进行了研究。序列分析表明 ,Rim2 5 6 9具有完整的 16 bp的末端颠倒重复序列 (TIRs)、若干正向和反向的 16 bp的亚末端重复 (STRs)以及插入位点 3 bp的同向重复。它的TIRs上具有保守序列CACTG ,有别于以往报告的CACTA转座子。该因子含有一个编码区 ,与已报告的Rim2cDNA的ORF基本一致 ,其预测编码蛋白与CAC TA转座子编码的转座酶TNP2和TNPD有低度的同源性。该亚组的其它因子的分子结构均与Rim2 5 6 9的相似 ,但这些因子预测ORF长度上存在着差异 ,反映了结构上的多样性。对检索到的Rim2因子的定位作图表明 ,它们在已测序拼接完成的第 1、4和 10号染色体上呈不均匀分布 ,以着丝点附近的分布频率为最高。PCR反应显示 ,Rim2编码因子在品种之间存在着编码序列多态性。

Different types of Rim2 elements constitute a super transposon family in rice genome that can be transcriptionally activated by the infection with rice blast pathogen Magnaporthe grisea . This study focuses on the structure and distribution of elements of transposase coding subgroup of this superfamily. A genomic clone of Rim2, Rim2 569 , was used for sequence and structural analysis. The results showed that Rim2 569 carried typical 16 bp terminal inverted repeats at both ends, 16 bp direct and inverted sub terminal repeats, and 3 bp target site duplication (Fig.1). Its characteristic sequence 'CACTG' in the terminal inverted repeats makes it different from CACTA elements (Table 1). Besides, it has a coding region almost identical to the reported Rim2 ORF and the putative protein shares a low similarity with the TNP2 and TNPD transposases encoded by CACTA elements (Fig.3). Other elements in this group share similar structure with Rim2 569 . They all contain the motifs of ClassⅡ elements, such as terminal inverted repeats, target site duplication and putative transposase. However, their putative transposases display a structural diversity in terms of the number of amino acid residues that are mostly truncated in N termini (Fig.2). In addition, an uneven distribution of identified Rim2 elements was discovered in the sequenced chromosomes 1, 4 and 10, with a dense distribution within centromeric regions (Fig.4). Finally, a polymorphism of Rim2 ORF was found among rice varieties examined (Fig.5).