Influence Of Simulated Microgravity On Repair Genes Expression After Radiation-induced DNA Damage

Space radiation and microgravity are two main factors to induce biological effects. Space radiation has the characteristics of high linear energy transfer (LET) and low-dose. The interaction between space radiation and microgravity is one of the research focuses in space biology. So far, the relevant research results show that the relationship between the two factors is not clear, including synergistic effect, antagonism effect, and independent effect, etc. In order to further clarify the relationship between them, we investigated the expressions of key repair protein in two major repair pathways for Arabidopsis thaliana, which included homologous recombination and non-homologous end joining.In the present work, the dry seed of wild type (WT) and pin2 mutant in Arabidopsis T. were exposed to carbon-ion beam with LET of 30 keV/μm and dose of 0.1 Gy. After the stable of germination rate of Arabidopsis T.,3-D Random Positioning Machine was used to simulate microgravity for 10-day. We measured the deflection angle of the root, the changes of expressions and locations of key repair proteins, including Ku70 and Rad51 by the laser confocal microscope.The results showed that, compared with the control, the deflection angle of the root in the WT Arabidopsis T. induced by the heavy ion radiation, microgravity and composite factors were significantly increased. In addition, compared with the radiation exposure, the deflection angle of the root induced by the composite factor was also significantly increased, while no significant changes were observed between the composite factor and the microgravity exposure.The results also showed that the expression of Ku70 induced by the composite factor were lower than that of radiation exposure in WT and pin2 mutant of Arabidopsis T.. While, compared with the control, a significant increasing was found in the expression of the composite factor and the radiation exposure. Comparing the positions of Ku70 in the nucleus, we found that the central position of nucleus was the main region of expression after radiation exposure. However, the edge area of nucleus was the main region of expression after composite factor. In addition, it was found that Rad51 was not changed in all three exposure conditions.In conclusion, we found that simulated microgravity could reduce radiation-induced DNA damage on the way to repair the non-homologous end joining. It is suggested that simulated microgravity and heavy ion radiation have antagonism effect under certain conditions.