Effect of light quality and 5-azacytidine on genomic methylation and stem elongation in two ecotypes of Stellaria longipes

Changes in cytosine methylation are known to occur in response to various e nvironmental stimuli, therefore, we looked at methylation changes in relati on to stem elongation. More specifically, we investigated the response of g enomic cytosine methylation to irradiance-mediated plasticity of stem elong ation in two ecotypes of Stellaria longipes, Ramets of S. longipes were gro wn under high and low ratios of red/far-red light (F/FR; 3.7 and 0.7, respe ctively). Stem elongation and methylated cytosine content were measured ove r a period of 7 days, Ramets of S, longipes demonstrated the highest level of demethylation after 4 days of long-day warm (LDW) treatment, which coinc ides with the first day of rapid stem elongation initiation, The extent of demethylation associated with day 4 depended upon the relative ratio of R/F R light. In particular, those plants treated with low R/FR light ratios sho wed a lower level of methylation, and were taller than the high R/FR light grown counterparts. In addition, prairie ecotype plants demonstrated lower day 4 methylation levels, as well as longer day 7 stem lengths, than the al pine ecotype plants within the same R/FR light treatments. To investigate i f the degree of methylation was a crucial factor in controlling the stem el ongation response, ramets of both alpine and prairie plants were grown in M S media supplemented with 5-azacytidine (5-AzaC), and grown for 14 days und er a R/FR ratio of 3.7 and two different PAR values, 5-AzaC treatments demo nstrated that the prairie ecotype plants required greater doses of 5-AzaC, and thus lower methylation levels, than the alpine ecotype plants in order to promote maximal stem elongation. These observations suggest that DNA dem ethylation is involved in the shade-avoidance response.