Scientists revealed the mechanism of Paramutation that multiple gene silencing pathways are involved in horizontal transmission. 

Biologists have paid more attention to the contribution of genetics of Mendelian to evolution and phenotypic plasticity, but the roles of Non-Mendelian is still underestimated. Paramutation is one of two exceptions for Non-Mendelian.  

Paramutation is an epigenetic phenomenon originally discovered in maize but has been observed in a number of other plant and animal organisms as well. The epigenetically silenced state of paramutated alleles is not only meiotically stable but also "infectious" to other active homologous alleles. The molecular mechanism of paramutation remains unclear but likely involves RNA-directed DNA methylation.  

The research group led by Dr. ZHU Jiankang of the Shanghai Center for Plant Stress Biology, Shanghai Institutes for Biological Sciences has discovered paramutation on the tandem repeats in a transgenic Arabidopsis. And the multiple gene silencing pathways are involved  in epigenetic inheritance and maintenance. The findings were published in the latest issue of Cell Reports. 

The study reported a multi-copy pRD29A-LUC transgene in Arabidopsis thaliana that behaves like a paramutation locus. The silent state of LUC is induced by mutations in the DNA glycosylase gene ROS1. The silent alleles of LUC can be maintained in the absence of ros1 mutations. Most importantly, they are not only meiotically stable but also able to transform active LUC alleles into silent alleles. Genetic analyses using multiple mutants that are defective in epigenetic regulation indicate that maintaining the silencing at the LUC gene requires action of multiple silencing pathways as well as other yet-to-be-identified factors. The study identified specific silencing factors that are involved in the paramutation-like phenomenon and established a model system to study paramutation in Arabidopsis.　 

This study will provide scientific evidence for the occurrence and inheritance of paramutation and epialleles, molecular breeding and evolution. 

Contact:
ZHENG Zhimin
Shanghai Center for Plant Stress Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences,
Shanghai 210602, China
zmzheng@sibs.ac.cn 

 Figure1: Characterization of the Paramutation-like Phenotype
"F" denotes filial generation of crosses; "BC" denotes crosses made with WT+LUC plants; "S" denotes self-crosses. (Image by Dr. ZHENG Zhiming) 

 Figure 2: The hypothesis of Paramutation mechanism in ArabidopsispRD29A-LUC transgene system (Image by Dr. ZHENG Zhiming)