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

Abstract

Changes in cytosine methylation are known to occur in response to various environmental stimuli, therefore, we looked at methylation changes in relation to stem elongation. More specifically, we investigated the response of genomic cytosine methylation to irradiance‐mediated plasticity of stem elongation in two ecotypes of Stellaria longipes. Ramets of S. longipes were grown under high and low ratios of red/far‐red light (F/FR; 3.7 and 0.7, respectively). Stem elongation and methylated cytosine content were measured over 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 coincides with the first day of rapid stem elongation initiation. The extent of demethylation associated with day 4 depended upon the relative ratio of R/FR light. In particular, those plants treated with low R/FR light ratios showed 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 alpine ecotype plants within the same R/FR light treatments. To investigate if the degree of methylation was a crucial factor in controlling the stem elongation response, ramets of both alpine and prairie plants were grown in MS media supplemented with 5‐azacytidine (5‐AzaC), and grown for 14 days under a R/FR ratio of 3.7 and two different PAR values. 5‐AzaC treatments demonstrated 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 demethylation is involved in the shade‐avoidance response.