Ectomycorrhizal-mediated lignin pathway activation enhances phosphorus use efficiency in Pinus massoniana

Phosphorus (P) is a key limiting nutrient for plant growth and productivity in forest ecosystems. Ectomycorrhizal (ECM) fungi are known to enhance host P uptake and stress resilience, the metabolic regulatory mechanisms underlying this symbiosis remain unclear in coniferous species. In this study, we investigated the role of Scleroderma citrinum colonization in modulating low-P tolerance and phenylpropanoid metabolism in Pinus massoniana . Physiological analyses revealed that under prolonged low-P conditions, ECM-inoculated seedlings exhibited significantly improved growth, root development, and organ-level P accumulation compared to non-inoculated controls, indicating effective mitigation of P deficiency. Transcriptomic profiling demonstrated that ECM symbiosis systemically activated key branches of the phenylpropanoid pathway: in needles, PmCAD1 , PmCAD2 , and PmPRX1 were upregulated to promote monolignol biosynthesis and polymerization; in roots, PmPRX2 , as well as several 4CL , BGL , and REF family genes, were co-induced, contributing to cell wall remodeling and signal interface optimization. To further validate these transcriptomic insights, we functionally characterized two key genes, PmCAD3 and PmPRX7 , confirming their roles in lignin biosynthesis. After 20 days of P-deficient treatment, transgenic lines displayed no marked phenotypic differences but accumulated significantly higher shoot P content than wild-type plants, confirming their role in enhancing P acquisition and tolerance. Collectively, our findings supports the conclusion that ECM symbiosis is likely to improve the structural and metabolic adaptability of P. massoniana to low-phosphorus environments by activating phenylpropanoid-lignin biosynthetic module. This study provides new molecular insights into ECM-regulated nutrient adaptation in conifers and offers a theoretical basis for breeding low-P-efficient forestry species. • Mycorrhizal symbiosis with Sc significantly enhances P uptake and growth performance of Pinus massoniana under low-P stress. • Transcriptome reveals that ectomycorrhizal colonization specifically activates the phenylpropanoid–lignin pathway. • Functional validation in Arabidopsis confirms that key mycorrhiza-responsive genes improve P accumulation under low-P stress.