The Roles Of The Copia-retrotransposons In Wheat On The Biological Effect Of The Low-energy N～+ Beam Implantation

Transposons, high copy numbers especially in eukaryotes, are transposable element in genome of a broad range of organism. They are divided into two families: DNA transposons and retrotransposons based on the propagation patterns. The retrotransposons family is divided into two main categories based on the presence and absence of long terminal repeats (LTRs): LTR-retrotransposons and non LTR-retrotransposons respectively. Retrotransposons are usually inactive in general, but retrotransposons are generally more transcriptionally active in the grasses than in other groups of plants. The activation strategy of retrotransposons offers the potential for explosive increases in copy number and leads to a concomitant genome size increase. Along the way of their propagation, retrotransposons could also cause the inserted mutagenesis in other genes, or could confer ecotopic regulatory functions upon adjacent genesWe have previously studied a wheat strain treated by low-energy N+ ion and found variations in AFLP (Amplified Fragment Length Polymorphism ) markers. One such variation is caused by re-activation of Tyl-copia-like Retrotransposons, implying that the mutagenic effects of low-energy ions might work through elevated activation of retrotransposons. The copia-retrotransposons are in the seedlings (24hr AG and 48hr AG) from the wheat seeds treated with 4×10¹⁷ N⁺/cm², transcripting in a higher level than that in the control. However, 72hr AG and 7dAG, the transcriptions of the copia-retrotransposons are the same level between the control samples and the treated sample.The sequences that obtained from the RT-PCR reactions of the treated sample have higher heterogeneity than that from the control sample;. The heterogeneity frequency (number of clones with different sequences/total number clones in control) is 81% (34/42) in the control sample, comparing to 97% (63/65)in the treated sample. Of these 34 unique control sequences, there are 16 (47%) have Nonsense mutations (table 1) and 20 (59%) have frame shift mutations. They are thus defective in coding. There are only 13 (38%) "intact" clones carrying neither frame shift nor nonsense mutations. There are 15 clones carrying both frame shift and nonsense mutations. Of these 63 unique sequences in treated samples clones, there are only 13 (21%) defective clones carrying nonsense mutations and 8 (13%) defective clones have frame shift mutations). They are thus defective in coding. There are 48 (76%) intact clones carrying neither a frame shift mutations nor nonsense mutations (table 1). There are only 6 clones carrying both a frame shift and nonsense mutation. Of these control group clones, 10 clones are clustered into family7, comprising 29.4% of the control group clones; 7 clones are clustered into family4, comprising 20.6% of these control group clones. Of these treated group clones, 24 clones are clustered into family7, comprising 38.7% of the control group clones; 20 clones are clustered into faimy4, comprising 32.3% of the control group clones. Phylogeny and classification are computed responding to the sequences of the RT domains. All the results show that there is much difference on RT domain between the control sample and the treated sample. Especially, the RT domains from the treated group encode significantly more functional ORF (open reading frames) than those from the control sample. This observation suggests that the treated sample has higher activation of retrotransposons, possibly as a consequence of low-energy ion beam irradiation. It also suggests that retrotransposons in the two groups impact the host gene expression in two different ways and carry out different functions in wheat cell.Low-energy ion beam as a abiotic stress promote the transcriptions of the copia-retransposons in those wheat buds cultivated at 24h and 48h, the comparative expression ratio of the copia-retransposons increased by different degree (max 220 fold) in those wheat treated in different doses(vacuum; 1×10¹⁷ N⁺/cm²; 3×10¹⁷ N⁺/cm²; 5×10¹⁷ N⁺/cm²; 7×10¹⁷ N⁺/cm²) of N⁺ beam comparing to that in the controls. Use of the IRAP and REMAP to detect the DNA isolated from the 14-day leaves of the wheat treated with the low-energy N⁺ beam showed that the transposition of some copia-retransposons was activated for the amplified polymorphic bands. The increased transcripts of the copia-retransposons in wheat regulate the expression and mRNA splicing of their near genes, the new insertion in genome change primary frame of the genes in the chromosomes, which have been visualized through the phenotype of the plants. Hence, it is suggested that the mechanisms about the biological effect of low-energy ion beam is partially attributed to the activation of the retrotransposons.We test the profiles of the expression of the genes adjacent to the retrotransposons Wis2-1A in the wheat treated with 5×10¹⁷ N⁺/cm² by the transposons display. The results showed that some genes adjacent to the retrotransposons Wis2-1A have been silent because of the transcription of the Wis2-1A under the implantation in the dose 5 ×10¹⁷ N⁺/cm²According to the all the results, it suggest that low-energy ion beam promote the activities of the transcription and transposition of the copia group retrotransposons in the wheat. In other word, the activities of the transcription and transposition of the copia group retrotransposons in the wheat play important roles in the biological effect of the low-energy ion beam, not only in the temporary generation but in the heritable biological effect of the low-energy ion beam. Of course, some ideas about the future strategy in this domain are argued.