A localized transcriptome at the synapse facilitates synapse-, stimulus-, and transcript-specific synthesis of the local proteome in response to neuronal activity. While enzyme-mediated mRNA modifications have been shown to regulate cellular mRNA turnover and translation, the role of these modifications in regulating synaptic RNA has not been studied. We established low-input m6A-seq of synaptosomal RNA to determine the chemically modified local transcriptome in healthy adult mouse forebrain and identified 4,329 selectively enriched m6A RNA peaks in 2,987 genes, which we refer to as the synaptic m6A epitranscriptome (SME). SME is functionally enriched in synthesis and modulation of tripartite synapses, and in pathways implicated in neurodevelopmental and neuropsychiatric diseases. Interrupting m6A-mediated regulation via knockdown of reader YTHDF1 in hippocampal neurons alters expression of SME member Apc, and causes synaptic malfunctions manifesting immature spine morphology and dampened excitatory synaptic transmission concomitant with decreased PSD-95 clustering and GluA1 surface expression. Our findings indicate that chemical modifications of synaptic mRNAs critically contribute to synaptic function.

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Phosphorus (P) limitation is a significant factor restricting crop production in agricultural systems, and enhancing the internal P-utilization efficiency (PUE) of crops plays an important role in ensuring sustainable P use in agriculture. To better understand how P is remobilized to affect crop growth, we first screened P-efficient (B73 and GEMS50) and P-inefficient (Liao5114) maize genotypes at the same shoot P content, and then analyzed P pools and performed non-targeted metabonomic analyses to explore changes in cellular P fractions and metabolites in maize genotypes with contrasting PUE. We show that lipid-P and nucleic acid-P concentrations were significantly lower in lower leaves of P-efficient genotypes, and these P pools were remobilized to a major extent in P-efficient genotypes. Broad metabolic alterations were evident in leaves of P-efficient maize genotypes, particularly affecting products of phospholipid turnover and phosphorylated compounds, and the shikimate biosynthesis pathway. Taken together, our results suggest that P-efficient genotypes have a high capacity to remobilize lipid-P and nucleic acid-P and promote the shikimate pathway towards efficient P utilization in maize.

Building and maintaining neuronal networks and cognitive functions require mRNA localization and regulated protein synthesis in neurons. RNA modification N6-methyl-adenosine (m6A) has recently been shown in axonal and synaptically localized mRNAs whose local activity is required for axon growth, synaptogenesis, and neuronal plasticity. However, no cellular pathways engaging local epitranscriptomic modulation are known to underlie these post-mitotic neuronal functions. Now we report that cytoplasmic m6A reader YTHDF1 is enriched in neurons and required for axonal, dendritic, and spine development. We show that m6A and YTHDF1 are part of a microtubule plus-end associated RNA granule that contains extensive networks of mRNAs organized by autism risk gene adenomatous polyposis coli (APC). Disrupting m6A signals by knocking down methyltransferase METTL14 or YTHDF1, or overexpressing autism or schizophrenia-associated missense mutations I311V or S399L in human METTL14, reduce expression of APC granule and tubulin, disrupt microtubule assembly and function. These results reveal a novel neuronal subcellular locus for epitranscriptomic regulation to promote post-mitotic neurodevelopment.