Transport of secondary metabolites in plants: Mechanistic insights and transporter engineering for crop improvement

Secondary metabolites (SMs) are essential for plant survival and adaptation, playing multiple roles in ecological interactions such as defense and stress tolerance. Specialized transporters relocate SMs from their synthesis sites to defense tissues or storage organs. The spatiotemporal distribution of defense-related SMs is a key determinant of plant fitness. However, the accumulation of anti-nutritional SMs in crop seeds or fruits can pose health risks to humans and livestock. Recent advances have revealed the critical role of SM transporters in optimizing metabolite allocation. This review examines the transport mechanisms of both defense and anti-nutritional SMs, with a particular focus on long-distance transporters that regulate source-sink dynamics and their potential applications in agricultural biotechnology. We highlight innovative strategies to manipulate transporter activity, ranging from multi-omics integration to precision engineering, and discuss how these approaches can be used to design crops with enhanced defense capacity, increased levels of beneficial compounds, and improved palatability of seeds and fruits. Finally, we outline emerging technologies and conceptual frameworks for discovering and characterizing long-distance SM transporters for crop improvement. Transporter-focused strategies offer promising solutions to global agricultural challenges and provide new opportunities for advancing crop improvement in the context of global food security.