Epigenetic Mechanism And Effects Of UV-B Radiation On Growth Of Clonal Plant Glechoma Longituba

Ultraviolet-B(UV-B)radiation in sunlight plays an important regulatory role for the growth and development of plants.With the progress of human industrialization and modernization,the decay of ozone layer and the increase of accompanying UV-B radiation on the ground can't be ignored.Studies have shown that epigenetic variation and its induced phenotypic plasticity are closely related to plant adaptation for new stress environments.However,compared with a large number of reports of epigenetic changes of plants in virous stress environments,the research for plants under UV-B stress condition is very scarce,and this is essential to reveal the effects of UV-B radiation on plants comprehensively,especially for explain the widespread distribution of clonal plants in various ecosystems.In the research,we planted the mother ramets of clonal plant Glechoma longituba in four environments(the absence of UV-B radiation,1-d UV-B radiation,20-d UV-B radiation,and40-d UV-B radiation),and the offspring ramets were grown under natural light conditions.At the end of the 41-day experiment,the growth indicators(biomass allocation,leaf area,specific leaf area(SLA))and defensive indicator(UV-B absorbing compounds)of the mother plant and the offspring ramets were measured to determine the effect of UV-B radiation on growth and phenotypic effects of G.longituba.Moreover,the methylation-sensitive polymorphism analysis(MSAP)technology was performed to analyze epigenetic variation(DNA methylation level)of ramets,so as to explore the following scientific questions:(1)Can G.longituba remember their UV-B radiation experience,and form epigenetic memory?(2)If yes,are the memory imprinting of different frequency UV-B was different?(3)How the UV-B environment of the mother ramet effect the growth of offspring ramets.The main results of this study were as follows:(1)G.longituba could form epigenetic memory of their UV-B radiation experience,which was displayed as a decrease of the total DNA methylation level.And the memory imprinting of different radiation frequencies was different,the total methylation degree gradually decreased with the increase of radiation frequency.(2)The UV-B radiation memory of the mother ramet could be transmitted across generations to offspring,but the timeliness of the memory varied with the radiation frequency.The memory of short-term UV-B radiation(1 day)was transient and reversible,while the memory of medium and high frequency radiation(20 and 40 days)was stable.(3)The different UV-B radiation experienced by the mother ramet would lead to different growth behaviors of the genet and the offspring,which led to different survival strategies.For example,if mother ramet was exposed to low-frequency UV-B radiation,the offspring grew randomly,that means,growth indicators(biomass,leaf area,and SLA)manifested as randomly among the different offspring ramets;when mother ramet was exposed to medium-frequency radiation,the offspring would grow uniformly;when mother plant was exposed to high-frequency radiation,the growth investment tended to the older offspring ramets.However,the investment allocation of defensive substances(UV-B absorbing compounds)was completely different.If mother ramet was in a low-frequency radiation environment,more defensive substances tended to be allocated to older offspring ramets;while if mother ramet was in a medium-high frequency radiation environment,the result was quite different,more defensive substance was distributed to younger offspring.In the end,the total biomass of the genet was promoted in the low-frequency radiation environment and suppressed in the medium-high frequency radiation.(4)The growth indexes of mother ramet was significantly affected by the changes their DNA methylation level caused by direct UV-B radiation,while UV-B absorbing compounds and SLA of ramets were related to the mother's DNA methylation level.In brief,the transgenerational effects of epigenetic memory and some phenotypic plasticity of G.longituba under UV-B radiation were frequency-dependent,and the variation of epigenetics,and phenotypes caused by different environments may lead to different growth behaviors.The results of this study can help us to comprehensively understand the mechanism of UV-B radiation on plants and the adaptive strategies of clone plants to the environment.