Cloning and structural analysis of the snap-back DNA of Pharbitis nil

Characterization of Tpn1 Family in the Japanese Morning Glory: En/Spm-related Transposable Elements Capturing Host Genes

Some mutant phenotypes are known to be unstable somatically and germinally due to the insertion of transposable elements in the Japanese morning glory (Ipomoea nil). Several transposable elements that cause mutable phenotypes have recently been isolated. All of these elements show characteristic features of the En/Spm (Enhancer/Suppressor-mutator) or CACTA family. They carry common 28 bp terminal inverted repeats and subterminal repetitive regions and are known as the Tpn1 family. All of these elements are thought to be non-autonomous and mobilized by unidentified autonomous element(s). Using a probe corresponding to the subterminal region, we isolated many genomic Tpn clones, 120 of which were classified into 28 types based on their restriction maps. The copy number of the Tpn1 family was estimated to be between 500 and 1,000 copies per haploid genome. We then determined the complete sequences of 28 representative clones from each Tpn type. Most Tpn elements showed a high degree of similarity to plant genes in their internal sequences, suggesting that the Tpn1 family captured host gene sequences during the process of evolution. Detailed analyses of Tpn104 in comparison with an orthologous host gene InAP2B confirmed this assumption.

Genomic organization of the 260 kb surrounding the waxy locus in a Japonica rice

The present study was carried out to characterize the molecular organization in the vicinity of the waxy locus in rice. To determine the structural organization of the region surrounding waxy, contiguous clones covering a total of 260 kb were constructed using a bacterial artificial chromosome (BAC) library from the Shimokita variety of Japonica rice. This map also contains 200 overlapping subclones, which allowed construction of a fine physical map with a total of 64 HindIII sites. During the course of constructing the map, we noticed the presence of some repeated regions which might be related to transposable elements. We divided the 260-kb region into 60 segments (average size of 5.7 kb) to use as probes to determine their genomic organization. Hybridization patterns obtained by probing with these segments were classified into four types: class 1, a single or a few bands without a smeared background; class 2, a single or a few bands with a smeared background; class 3, multiple discrete bands without a smeared background; and class 4, only a smeared background. These classes constituted 6.5%, 20.9%, 3.7%, and 68.9% of the 260-kb region, respectively. The distribution of each class revealed that repetitive sequences are a major component in this region, as expected, and that unique sequence regions were mostly no longer than 6 kb due to interruption by repetitive sequences. We discuss how the map constructed here might be a powerful tool for characterization and comparison of the genome structures and the genes around the waxy locus in the Oryza species.

Classification and relationships of rice strains with AA genome by identification of transposable elements at nine loci

We analyzed the presence of p-SINE1 members at five loci in the rice strains belonging to seven species with AA genome in the Oryza genus by the methods including polymerase chain reaction (PCR). Four p-SINE1 members (p-SINE1-r3, r4, r5 and r7) were present at the corresponding loci in all the strains examined. One member (p-SINE1-r6) was, however, not present at the corresponding locus in most of the African strains of O. glaberrima and O. barthii, but was in the other strains. The PCR-amplified fragments containing p-SINE1-r4 in many strains were found to be larger due to insertion of either one of two transposable elements, named Tnr2 and Ret1, within or near p-SINE1-r4, respectively: Tnr2 is 157 bp in length with terminal inverted repeat sequences of about 56 bp; Ret1 is only 13 bp in length with a T stretch at its end. Tnr2 was not present in the corresponding locus in all the strains belonging to O. sativa Japonica and in some strains of O. rufipogon and O. longistaminata, while Ret1 was present only in the two strains of O. longistaminata. These results and previous ones obtained from the analysis of the other two p-SINE1 members (p-SINE1-r1 and r2) in the Wx gene indicate that the elements, such as p-SINE1-r6, Tnr2, Ret1 and p-SINE1-r2, have been inserted into the respective loci during divergence of the rice species with AA genome. The patterns for the presence and absence of the transposable elements at the respective loci enabled us to classify the rice strains with AA genome into ten groups and to infer their relationships.