In most plants, centromeric DNA contains highly repetitive sequences, including tandem repeats and retrotransposons; however, the roles of these sequences in the structure and function of the centromere are unclear.
Recently, a research made by the team led by HAN Fangpu at University of Chinese Academy of Sciences and Institute of Genetics and Developmental Biology, CAS, addressed the interaction between CRMs and centromere structure and function. The research team found that multiple RNA sequences from centromeric retrotransposons (CRMs) were enriched in maize (Zea mays) centromeres, and back-spliced RNAs were generated from CRM1. The study identified 3 types of CRM1-derived circular RNAs with the same back-splicing site based on the back-spliced sequences. These circular RNAs bound to the centromere through R-loops. Two R-loop sites inside a single circular RNA promoted the formation of chromatin loops in CRM1 regions. When RNA interference (RNAi) was used to target the back-splicing site of the circular CRM1 RNAs, the levels of R-loops and chromatin loops formed by these circular RNAs decreased, while the levels of R-loops produced by linear RNAs with similar binding sites increased. Linear RNAs with only one R-loop site could not promote chromatin loop formation. Higher levels of R-loops and lower levels of chromatin loops in the CRM1 regions of RNAi plants led to a reduced localization of the centromeric H3 variant (CENH3). The study reveals centromeric chromatin organization by circular CRM1 RNAs via R-loops and chromatin loops, which suggested that CRM1 elements might help build a suitable chromatin environment during centromere evolution. These results highlight that R-loops are integral components of centromeric chromatin and proper centromere structure is essential for CENH3 localization.
The study is published in PLOS Biology entitled “Back-spliced RNA from retrotransposon binds to centromere and regulates centromeric chromatin loops in maize” on January 29. LIU Yalin and SU Handong at University of Chinese Academy of Sciences are the first authors of the study, HAN Fangpu is the corresponding author. This work was supported bu the National Natural Science Foundation of China (NSFC). XIAO Xue (Institute of Physics, CAS) , HANG Runlai from the laboratory of CAO Xiaofeng (Institute of Genetics and Developmental Biology, CAS), SHEN Jie from the laboratory of LI Guohong (Institute of Biophysics, CAS), YE Xingguo (Institute of Crop Science, Chinese Academy of Agricultural Sciences), TIAN Zhixi and XIE Qi (Institute of Genetics and Developmental Biology, CAS) also contributed to the study.
