Specialized Metabolic Reprogramming in Plant Immunity: Biosynthetic Networks, Spatiotemporal Regulation, and Quantitative Defense

Specialized metabolic reprogramming is a central component of plant immunity. However, its integration across biosynthetic networks and defense phenotypes remains incompletely understood. This mini review examines how specialized metabolites are produced, regulated, spatially deployed, and linked to defense outcomes. We highlight how metabolites such as camalexin, indolic glucosinolates, benzoxazinoids, flavonoids, lignin precursors, pipecolic acid, and N-hydroxypipecolic acid are produced through pathway branching, metabolic flux redistribution, and coordination with primary metabolism. We further discuss how immune signaling modules and transcriptional regulators, including salicylic acid, jasmonic acid, and ethylene pathways, together with transcription factors, regulate defense mechanisms through genes such as PAD3, CYP71A12, CYP71A13, ALD1, SARD4, FMO1, JAZ, and ORA59. Emphasis is placed on spatiotemporal compartmentation, including cell- and tissue-specific responses, plastidial and endoplasmic reticulum-associated metabolism, vacuolar sequestration, apoplastic deployment, and transport-dependent localization, as metabolite function depends greatly on when and where compounds accumulate. This review also evaluates how these metabolic programs are translated into quantitative defense phenotypes, such as resistance outcomes, growth-defense tradeoffs, and fitness costs. Finally, we evaluate emerging tools, including metabolomics, spatial metabolomics, multiomics integration, network inference, and predictive modeling, to elucidate causal relationships between metabolic reprogramming and immune performance. Collectively, the evidence supports a multiscale framework in which specialized metabolism links immune perception to quantitative defense output.