Mobilization Of Transposon MPing And Heritable Alterations In DNA Methylation Pattern Induced By Laser Irradiation In Rice(cv.Nipponbare)

External stresses on plants can be divided into those of biotic and abiotic.They exert strong evolutionary pressure on all organisms,and organisms need to develop some mechanisms like resistance,tolerance and avoidance to survive.Plants can not escape from the stress conditions,and they mainly develop sophisticated responses to survive which involve cellular physiology,gene regulation and genome remodeling.Transposons have many copies and account for most important part in eukaryotic cell genome,and they can insert into new chromosomal locations and often make duplicate copies of themselves in the process.It has been shown that plants' transposon mobilization can be affected by the epigenetic mechanisms such like the change of DNA methylation and siRNA under abiotic stress conditions.As a result,the structure of plant genome and expression of genes can be remolded for the activation of some transposable elements.The miniature-Ping(mPing) is a recently isolated active miniature inverted-repeat transposable element(MITE) from rice,which was mobilized by tissue culture andγ-ray irradiation.Our laboratory has found that He-Ne laser can induce the activation of mPing and the change of DNA methylation at the cultivar JL01-124.On the basis of this work, we have further studied the issue and show here that there were many phenotypic mutants after the Nipponbare seeds were irradiated by the He-Ne laser.We thus tested the mobilization of mPing and Pong in this phenotypic mutants by Southern blot and locus-specific PCR assays at the M₁ and M₂ selfed generations.We got results that laser irritation could induce the activation and new insertion of mPing and Pong;the offsprings of M₁ and M₂ could stably inherit these mobilizations by meiosis;there was no further activation of mPing in the crossbreeds of M₁ and nipponbare.We also tested the DNA methylation variation in M₀ M₁ and M₂ somatic cells by Southern blot,and found that most of the genes and transposons changed the methylation level in CCGG loci,and the changes could be transferred to offsprings stably.There were also some plants occured reverse mutation or showed more changes in next generation.