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

Secondary metabolites (SMs) are crucial for plant survival and adaptation and play multiple roles in mediating ecological interactions, such as defense and stress tolerance. Specialized transporters relocate SMs from 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 may pose health risks to humans and livestock. Recent advances have highlighted the significant role of SM transporters in optimizing the allocation of metabolites. This review explores the transport mechanisms for both defense and anti-nutritional SMs, focusing on long-distance transporters that regulate source-sink dynamics and their potential implications in agricultural biotechnology. We highlight innovative approaches to manipulating transporter activities, ranging from multi-omics integration to precision engineering, and discuss how these tools can be used to design crops with enhanced defense capacity, increased levels of beneficial compounds, and more palatable seeds and fruits. We explore the technologies and frameworks for the discovery and characterization of long-distance transporters of SMs for crop improvement. Transporter-focused frameworks offer a promising solution to global agricultural challenges and present exciting opportunities for advancing crop improvement in the context of global food supply.