Multiple genetic processes result in heterogeneous rates of evolution within the major cluster disease resistance genes in lettuce
Multiple genetic processes result in heterogeneous rates of evolution within the major cluster disease resistance genes in lettuce
复制标题
DOI：
10.1105/tpc.104.025502
复制
发表时间：
2004-11-01
期刊：
影响因子：
11.6
通讯作者：
Michelmore, RW
中科院分区：
文献类型：
--
作者：
Kuang, H;Woo, SS;Michelmore, RW
抗病基因RGC 2（Resistance Gene Receptate 2）基因是莴苣（Lactuca sativa）中一个高重复的多核苷酸结合位点-富含亮氨酸重复序列（NBS-LRR）基因家族。为了研究该基因座进化过程中发生的遗传事件，对莴苣属3个种的7个基因型的126个RGC 2基因的1.5 - 2kb 3'端片段进行了测序，并从40份莴苣属野生材料中获得了107个额外的RGC 2序列。RGC 2基因的拷贝数从12到32不等，每个基因组在7个基因型广泛研究。LRR数量从40到47不等，这种变化的大部分是由于13个事件重复2至5个LRR，因为在两个重组热点之一的RGC 2基因内或之间的不平等交换。两种类型的RGC 2基因（I型和II型）最初基于它们的3'区域之间的序列同一性模式来区分。两种类型的RGC 2基因的存在进一步支持内含子的相似性，序列交换的频率，以及它们在自然人群中的流行。I型基因是由频繁的序列交换引起的广泛嵌合体。I型基因之间频繁的序列交换均质化了内含子序列，而不是编码序列，并且模糊了等位基因/正等位基因的关系。来自额外的野生种质的I型基因的测序证实了高频率的序列交换和自然界中存在许多嵌合RGC 2基因。与I型基因不同，II型基因在旁系同源序列之间表现出罕见的序列交换。莴苣属内不同基因型/种的II型基因表现出明显的等位/正等位关系。观察到不同组的直系同源物的反式特异性多态性，这表明平衡选择。不平等的交叉，插入/缺失，和点突变事件分布不均匀的基因。不同的进化力量影响了LRR的不同部分。
Resistance Gene Candidate2 (RGC2) genes belong to a large, highly duplicated family of nucleotide binding site-leucine rich repeat (NBS-LRR) encoding disease resistance genes located at a single locus in lettuce (Lactuca sativa). To investigate the genetic events occurring during the evolution of this locus, similar to1.5- to 2-kb 3' fragments of 126 RGC2 genes from seven genotypes were sequenced from three species of Lactuca, and 107 additional RGC2 sequences were obtained from 40 wild accessions of Lactuca spp. The copy number of RGC2 genes varied from 12 to 32 per genome in the seven genotypes studied extensively. LRR number varied from 40 to 47; most of this variation had resulted from 13 events duplicating two to five LRRs because of unequal crossing-over within or between RGC2 genes at one of two recombination hot spots. Two types of RGC2 genes (Type I and Type II) were initially distinguished based on the pattern of sequence identities between their 3' regions. The existence of two types of RGC2 genes was further supported by intron similarities, the frequency of sequence exchange, and their prevalence in natural populations. Type I genes are extensive chimeras caused by frequent sequence exchanges. Frequent sequence exchanges between Type I genes homogenized intron sequences, but not coding sequences, and obscured allelic/orthologous relationships. Sequencing of Type I genes from additional wild accessions confirmed the high frequency of sequence exchange and the presence of numerous chimeric RGC2 genes in nature. Unlike Type I genes, Type II genes exhibited infrequent sequence exchange between paralogous sequences. Type II genes from different genotype/species within the genus Lactuca showed obvious allelic/orthologous relationships. Trans-specific polymorphism was observed for different groups of orthologs, suggesting balancing selection. Unequal crossover, insertion/deletion, and point mutation events were distributed unequally through the gene. Different evolutionary forces have impacted different parts of the LRR.