Drought-induced Alterations In Cytosine Methylation In The Rice Genome

Drought is an important and offen-occurring abiotic stress faced by agriculture. To simulate drought stress, rice cultivar Matsumae and its derived introgression lines (RZ1, RZ2 and RZ35) were treated with 15% PEG at various intervals, 4 hours, 1 day and 6 days, respectively. The DNA methylation states and alterations were examined by the method of MSAP. A total of 536, 554, 554 and 562 bands were amplified respectively for the plant lines. It was found that the patterns of DNA methylation changed after the PEG treatments, with the highest alteration frequency occurred in the Matsumae/4-hour treatment, which was 54% of the methylation-sensitive sites, and the lowest alteration frequency occurred in the Matsumae6-day treatment, which was 10%. In contrast to Matsumae, RZ35 showed a sharp difference in terms of the occurrence of methylation alterations, with the highest alteration occurred in the 1-day treatment. For the three time point examined, DNA methylation variation culminated at the first time and then fell rapidly in Matsumae, RZ1 and RZ2, while it raised and then fell slowly in RZ35. It is believed that the special characteristics of RZ35 compared with other rice lines might be due to its outstanding tolerance to various stress conditions. Fifteen variable MSAP profiles were isolated and sequenced, and results showed that they all included a CCGG site in one of the terminus, vaifying reliability of the MSAP method. BlastN analysis mapped the 15 MSAP profiles onto different rice chromosomes. BlastX analysis showed that 4 of the profiles represent active genic sequences. Southern blot analysis validated the authenticity of the methylation alterations detected by MSAP. It thus seemed that alterations in DNA cytosine methylation represent one of the responses by the rice genome to drought stress.