N6-methyladenosine-mediated feedback regulation of abscisic acid perception via phase-separated ECT8 condensates in Arabidopsis.

N6-methyladenosine (m6A) is the most abundant internal modification in eukaryotic mRNAs, yet how plants recognize this chemical modification to swiftly adjust developmental plasticity under environmental stresses remains unclear. Here we show that m6A mRNA modification and its reader protein EVOLUTIONARILY CONSERVED C-TERMINAL REGION 8 (ECT8) act together as a key checkpoint for negative feedback regulation of abscisic acid (ABA) signalling by sequestering the m6A-modified ABA receptor gene PYRABACTIN RESISTANCE 1-LIKE 7 (PYL7) via phase-separated ECT8 condensates in stress granules in response to ABA. This partially depletes PYL7 mRNA from its translation in the cytoplasm, thus reducing PYL7 protein levels and compromising ABA perception. The loss of ECT8 results in defective sequestration of m6A-modified PYL7 in stress granules and permits more PYL7 transcripts for translation. This causes overactivation of ABA-responsive genes and the consequent ABA-hypersensitive phenotypes, including drought tolerance. Overall, our findings reveal that m6A-mediated sequestration of PYL7 by ECT8 in stress granules negatively regulates ABA perception, thereby enabling prompt feedback regulation of ABA signalling to prevent plant cell overreaction to environmental stresses.

N6-methyladenosine modification underlies messenger RNA metabolism and plant development.

RNA modifications constitute an essential layer of gene regulation in living organisms. As the most prevalent internal modification on eukaryotic mRNAs, N6-methyladenosine (m6A) exists in many plant species and requires the evolutionarily conserved methyltransferases, demethylases, and m6A binding proteins for writing, erasing, and reading m6A, respectively. In plants, m6A affects many aspects of mRNA metabolism, including alternative polyadenylation, secondary structure, translation, and decay, which underlies various plant developmental processes and stress responses. Here, we discuss the recent progress in understanding the roles of m6A modification in mRNA metabolism and their mechanistic link with plant development and stress responses. We also highlight some outstanding questions and provide an outlook on future prospects of m6A research in plants.

Use of digital gene expression to discriminate gene expression differences in early generations of resynthesized Brassica napus and its diploid progenitors.

BACKGROUND: Polyploidy is an important evolutionary mechanism in flowering plants that often induces immediate extensive changes in gene expression through genomic merging and doubling. Brassica napus L. is one of the most economically important polyploid oil crops and has been broadly studied as an example of polyploid crop. RNA-seq is a recently developed technique for transcriptome study, which could be in choice for profiling gene expression pattern in polyploids. RESULTS: We examined the global gene expression patterns of the first four generations of resynthesized B. napus (F1-F4), its diploid progenitors B. rapa and B. oleracea, and natural B. napus using digital gene expression analysis. Almost 42 million clean tags were generated using Illumina technology to produce the expression data for 25959 genes, which account for 63% of the annotated B. rapa genome. More than 56% of the genes were transcribed from both strands, which indicate the importance of RNA-mediated gene regulation in polyploidization. Tag mapping of the B. rapa genome generated 19023, 18547, 24383, 20659, 18881, 20692, and 19955 annotated genes for the B. rapa, B. oleracea, F1-F4 of synthesized B. napus, and natural B. napus libraries, respectively. The unambiguous tag-mapped genes in the libraries were functionally categorized via gene ontological analysis. Thousands of differentially expressed genes (DEGs) were identified and revealed the substantial changes in F1-F4. Among the 20 most DEGs are DNA binding/transcription factor, cyclin-dependent protein kinase, epoxycarotenoid dioxygenase, and glycine-rich protein. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of the DEGs suggested approximately 120 biological pathways. CONCLUSIONS: The systematic deep sequencing analysis provided a comprehensive understanding of the transcriptome complexity of early generations of synthesized B. napus. This information broadens our understanding of the mechanisms of B. napus polyploidization and contributes to molecular and genetic research by enriching the Brassica database.