Tandem duplication underlies diversification of the gymnosperm-specific TPS-d subfamily

Terpene synthases (TPSs) are key drivers of terpenoid diversity in plants, yet the diversity and mechanisms driving their diversification in gymnosperms remain poorly understood. Through comparative genomic analyses of 16 representative land plant species, we demonstrate that tandem duplication (TD) plays an important role in the expansion of gymnosperm-specific TPS-d subfamily. These TD-generated TPS-d genes exhibit elevated sequence variability and markedly increased tissue specificity (τ) compared with conserved primary-metabolic TPS-c and TPS-e/f genes, indicating rapid functional and regulatory divergence following duplication. Together, our results propose a comprehensive evolutionary framework that illustrates how TD, sequence divergence, and expression diversification collectively shape TPS-d gene evolution in gymnosperms, providing new insights into lineage-specific terpenoid profiles and ecological adaptation in gymnosperms.