Phytochrome B and the methyltransferase complex coordinately regulate N⁶-methyladenosine RNA modification and shade...

Shade avoidance is a critical adaptive strategy that plants employ to respond to competition. N⁶-methyladenosine (m⁶A), the most abundant and dynamic mRNA modification, has emerged as a key epigenetic mechanism regulating adaptive responses. Here, we demonstrate that shade significantly reduces global m⁶A levels in a manner dependent on phytochrome B (phyB) and the m⁶A methyltransferase complex (MTC). Shade attenuates the interaction between phyB and the MTC, impairing both the RNA-binding capacity and methyltransferase activity of the complex. Transcriptome-wide m⁶A profiling revealed that shade treatment and phyB mutation similarly reduce m⁶A modification, particularly on transcripts involved in auxin and abscisic acid (ABA) signaling. Phenotypic analyses further showed that the MTC is required for shade-induced hypocotyl elongation and ABA hypersensitivity. Mechanistically, shade-induced m⁶A reduction enhances the stability of SAUR15/19/20 transcripts while decreasing the translation efficiency of ABA signaling repressors SCHNARCHZAPFEN, MYB20, and PROPEP3. Our findings uncover a mechanism by which phyB modulates m⁶A deposition to fine-tune plant elongation growth and stress adaptation under shade.