Characteristics of N-methyladenosine Modification During Sexual Reproduction of Chlamydomonas reinhardtii.

The unicellular green alga Chlamydomonas reinhardtii (hereafter Chlamydomonas) possesses both plant and animal attributes, and it is an ideal model organism for studying fundamental processes such as photosynthesis, sexual reproduction, and life cycle. N-methyladenosine (mA) is the most prevalent mRNA modification, and it plays important roles during sexual reproduction in animals and plants. However, the pattern and function of mA modification during the sexual reproduction of Chlamydomonas remain unknown. Here, we performed transcriptome and methylated RNA immunoprecipitation sequencing (MeRIP-seq) analyses on six samples from different stages during sexual reproduction of the Chlamydomonas life cycle. The results show that mA modification frequently occurs at the main motif of DRAC (D = G/A/U, R = A/G) in Chlamydomonas mRNAs. Moreover, mA peaks in Chlamydomonas mRNAs are mainly enriched in the 3' untranslated regions (3'UTRs) and negatively correlated with the abundance of transcripts at each stage. In particular, there is a significant negative correlation between the expression levels and the mA levels of genes involved in the microtubule-associated pathway, indicating that mA modification influences the sexual reproduction and the life cycle of Chlamydomonas by regulating microtubule-based movement. In summary, our findings are the first to demonstrate the distribution and the functions of mA modification in Chlamydomonas mRNAs and provide new evolutionary insights into mA modification in the process of sexual reproduction in other plant organisms.