Impact of m6A Modification and Transcript Quantity on mRNA Composition in Plant Stress Granules.

Abstract

Stress granules (SGs) are cytoplasmic structures that emerge in response to unfavorable environmental conditions. The mechanisms governing the accumulation of transcripts in SGs are only partially understood. Despite the recognized role of N6-methyladenosine (m6A) in plant transcriptome regulation, its impact on SGs' composition and assembly remains elusive. In Lupinus angustifolius, SGs display a distinctive bi-zonal structure comprising of a ring and a central area with differences in ultrastructure and composition. Subsequent to the transcriptome analysis, specific mRNA were chosen to investigate their localization within SGs and assess m6A levels. Transcripts of hypoxia-responsive genes (ADH1 and HUP7) showed significantly lower levels of m6A compared to housekeeping genes, but only ADH1 was absent in SGs. HUP7 mRNA, characterized by a low quantity of m6A, is present both in the SGs and cytoplasm, probably due to extremely high expression level. The m6A was observed only during the assembly of SGs. In mutants of Arabidopsis thaliana with reduced levels of m6A, ECT2 (reader of m6A) was not observed in SGs, and poly(A) RNA levels and the number of SGs were reduced. In summary, our findings demonstrate a limited impact of m6A modification on SGs assembly. However, the interplay between m6A modification and the overall transcript quantity in the cytoplasm appears to play a regulatory role in mRNA partitioning and assembly of SGs.