Ground simulation evaluation on mutation effects induced by heavy ions in sweet sorghum

With the development of space research, plant becomes an excellent model to investigate the biological effects of ionizing radiation for assessing the damage of the space environment. Sweet sorghum is a C4 plant, making it an attractive model plant for functional genomics because of its small genome (_730 Mb).In our research, the dry seeds of sweet sorghum were irradiated by carbon ions with different doses, generated by the Heavy Ion Research Facility in Lanzhou (HIRFL) facility, Institute of Modern Physics, Chinese Academy of Sciences. The results showed that the survival fraction presented "saddle like model" that the survival rate decreased, then increased and decreased again with irradiation doses increased. Although the differences between doses were small at 10, 20 and 30 Gy for the phenotypic variations, the carbon ions had a marked stimulatory effect on the survival rate at low doses, with the value at 30 Gy being 86%, higher than that of non-irradiated seeds. After carbon ion irradiation, some abnormal mutants, such as growing point vanishing, tip curling, plant withering and etiolation, were obtained at the seedling stage. At the same time, an early-maturity mutant, KFJT-1, was isolated at 80 Gy, which the growth period was shortened by about 20 days compared to the wild type KFJT-CK. Physiological analysis showed that the proline content of KFJT-1 was increased by 11.05% while the malondialdehyde content was significantly lower than that of KFJT-CK. Regarding to the characteristic of KFJT-1, the expression of the circadian rhythm genes was investigated by RNA-seq analysis, which indicated that a critical photoreceptor PHYA gene was significantly up-regulated in leaf and root of KFJT-1, suggesting the mutation could occur on the genomic upstream of PHYA. In conclusion, our work will provide helpful insights to further understand the mutation effects of heavy ions and assess the damage of the space environment in the future.