N 6-Methyladenosine (m6A) in Horticultural Crops: A Review of Functions and Research Gaps

N 6 -methyladenosine (m6A), the most abundant internal mRNA modification in eukaryotes, is a dynamic and reversible epitranscriptomic mark regulated by m6A methyltransferases (writers), demethylases (erasers), and reader proteins (readers). By modulating mRNA stability, alternative splicing, and translation efficiency, m6A modification contributes to essential horticultural traits, including fruit ripening and shelf life, floral color and morphology in ornamentals, long-term stress adaptation in woody crops, accumulation of bioactive compounds in medicinal plants and graft compatibility. Advances in methylated RNA immunoprecipitation sequencing (MeRIP-seq) and nanopore direct RNA sequencing have enabled transcriptome-wide m6A profiling. However, mechanistic and functional validation in horticultural crops remains limited to a small number of model species and major crops. This leaves the epitranscriptomic landscapes of many economically valuable fruits, vegetables, ornamentals, and medicinal plants largely underexplored, and horticulture-specific m6A regulatory patterns remain insufficiently integrated. Here, we synthesize evidence from 189 plant species (categorized into core horticultural, broadly relevant, and reference species) to summarize current knowledge of m6A-associated regulatory roles and highlight translational opportunities for trait improvement. This review provides a comprehensive, horticulture-tailored functional reference for fruit biology, vegetable breeding, and ornamental and medicinal plant research. Future priorities include developing specialized m6A detection platforms for polysaccharide-rich woody tissues, establishing m6A-based molecular breeding systems, such as marker-assisted selection for fruit shelf life and stress tolerance, and overcoming functional validation bottlenecks in non-model horticultural crops. These efforts may facilitate the translational application of m6A-based regulation in horticultural crop improvement.