DNA Methylation Variation Of Invasive Alternanthera Philoxeroides In Response To Salt Stress

Epigenetic modification, e.g. DNA methylation, can change the pattern of gene expression without altering underlying DNA sequences. Environmental stress can induce variable DNA methylation, which might be adaptive. Many studies of DNA methylation focus on model species or crop species (e.g. Arabidopsis, Oryza), and less attentions are paid to the ecologically important species. Alternanthera philoxeroides is one of the most harmful invasive plants in China, spreading mainly by asexual reproduction, in which epigenetic modifications may play an important role in its adaption in heterogeneous habitats. In this study, using six genotypes of A.philoxeroides, we examined the DNA methylation variation in response to salt stress, with an emphasis on the effects of different genotypes, stress timing (i.e. different developmental stages of asexual seedlings), and stress duration.In this study, plants of different developmental stages (asexual seedling VS adult plants) of A.philoxeroides plants were treated using 0.2M NaCl, with different duration (7 days VS 30 days). Six replications were used for each treatment. The methylation-sensitive amplified polymorphism(MSAP) markers were used to detect the changes of methylation pattern in response to salt stress. For each of the two enzyme-combination (i.e. Hpa Ⅱ/EcoR Ⅰ and Msp Ⅰ/EcoR Ⅰ),10 primers were used. For 180 samples, each produced 988 repeatable and clear bands. The absence and presence of band were recorded as 0 or 1, and data were analyzed. The results were summarized as below:(1) Salt stress can significantly increase the levels of epigenetic variation within population. We fail to find consistent methylation changes in response of salt stress at certain locus across different individuals. Instead, all treatment groups had significant higher levels of DNA methylation variation than the corresponding control groups.(2) The effect of salt stress is related to developmental stage. Compared with cuttage seedlings, adult plants were more sensitive to salt stress. In case of salt stress, the Shannon diversity index ranges from 0.001 to 0.008 in seedling groups but from 0.016 to 0.035 in adult groups.(3) The effect of salt stress on DNA methylation variation increased with the treatment duration, ranging from 0.005-0.014 (7 days) to 0.016-0.032 (30 days).(4) Variable genotypes have significant different responses of DNA methylation under salt stress, with consistent results for the two combinations of restriction endonucleases (i.e. Hpa Ⅱ/EcoR Ⅰ and Msp Ⅰ/EcoR Ⅰ).Taken together, salt stress can induce significant changes of DNA methylation in A. philoxeroides, especially the increase of epigenetic variation within populations. The effect size seems to be affected by plant genotypes, developmental stage, and treatment duration. Such increased epigenetic diversity within populations under stress may be essential for adaptation in the clonal invasive species like A. philoxeroides.