Alteration of DNA methylation level and pattern in sorghum (Sorghum bicolor L.) pure-lines and inter-line F1 hybrids following low-dose laser irradiation

Low-dose laser irradiation can stimulate a number of biological processes and has been widely used in various fields including producing useful mutants in crop improvement. Nonetheless, the molecular and genetic basis for the mutagenic property of low-dose laser irradiation has not been elucidated. DNA cytosine methylation is sensitive and responsive to both intrinsic perturbations and environmental cues. This study was aimed to probe the possible effect of low-dose laser irradiation on stability of DNA methylation in sorghum pure-lines and intraspecific F1 hybrids. For this purpose, a pair of Sorghum bicolor L. reciprocal F1 hybrids and their parental pure-lines was used, and their germinating seeds were treated by low-dose laser irradiation. The level and pattern of DNA methylation in the plants were analyzed by methylation-sensitive amplified polymorphism (MSAP). Results showed that low-dose laser irradiation induced low-frequency but significant alterations in DNA methylation level and pattern in sorghum plants, demonstrating the treatment is epigenetically mutagenic in plants. In addition, we observed that the alteration frequency in the inter-line F1 hybrids was higher than that of their pure-line parents, suggesting an interaction of hybridity and the laser irradiation. We propose that the combined use of intraspecific hybridization and an epigenetically mutagenic treatment like low-dose laser irradiation might be a useful means to generate heritable epigenetic variations in plants.