VII. 
Gene expression and function
50. 
Expression of RAD5I -like genes in japonica rice.
Y. AKAMA1, J. Shimazu1, M. Niizeki1,2, M. SENDA2, R. ISHIKAWA’, S. AKADA2 and T. HARADA’
1) 
Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, 036-8561 Japan
2) 
Gene Research Center, Hirosaki University, Hirosaki, 036-8561 Japan

 
 
    Genetic variations which have often arisen through cell cultures in many species of plants have became known as somaclonal variation (Larkin and Scowcroft 1981). However, the mechanism of somaclonal variation is as yet unclear from many perspectives. In order to clarify the mechanism, we focused on mitotic homologous recombination.
     The RecA-like genes which are essential to homologous recombination of DNA strands are classified into LIMI5/DMCI-type and RAD5J-type genes in eukaryotes (Stassen eta!. 1997). The LJMJ5/DMCI-type gene is specifically expressed for homologous recombination during meiosis (Bishop eta!. 1992, Habu eta!. 1996, Kjimyuk and Jones 1997). The RAD5I-type is expressed for meiotic homologous recombination and the repair of double- strand breaks of DNA (Shinohara et a!. 1992, Aboussekhra et al. 1992, Basile et a!. 1992). In rice, the LIMI5IDMCI-type gene, RiLJMI5, was isolated by Sato et a!. (personal communication) and was expressed not only in meiotic young panicles, but also in mitotic cultured cells (Shimazu et a!. 1998). However, the RAD51 gene has not been isolated yet from rice. In this study, we tried to isolate the RAD5I-type gene from rice, and also investigate the function of the gene. The results are as follows.
1. RecA-like genes consist of three domains, and domain II is highly homologous among RecA -like genes. Therefore, we focused on domain II and performed PCR. By using primers designed by the sequences of the RAD5J gene of tomato and Arabidopsis, PCR was performed using leaf genomic DNA of strain A58. The sequence of the PCR product was determined and compared with those of tomato and Arabidopsis. Homologies to the RAD51 sequences of tomato and Arabidopsis were 81% and 82%, respectively. Homologies of the amino acid sequences predicted by the DNA sequence to those of tomato and Arabidopsis were 95% and 97%, respectively.
2. Reverse transcription-polymerase chain reaction (RT-PCR) was performed using total RNA extracted from the cultured cells, young meiotic panicles, mature leaves and X-ray treated seedlings (Fig. 1). Expression of the RAD5J-like gene was found to occur in cultured cells, young meiotic panicles and X-ray treated seedlings, but not in mature leaves. This result shows that the RAD5J-like gene possibly participates in DNA repairing. Thus, it is likely that the RiLIM1S and RAD5I genes may have different functions on the homologous recombination of DNA strands. The expression of RAD51-like gene of rice during meiosis and after X-ray irradiation are similar to those RAD5J -type genes expressed in other species (Basile eat al. 1992, Bishop et a!. 1992, Shinohara et a!. 1992, Habu eat a!. 1996, Klimyuk and Jones 1997, Stassen eat a!. 1997). The expression of RAD5J-like gene in cultured cells may be related to the mitotic homologous recombination.
 


 

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