Gene Family Expansion and Functional Diversification of β‐Ketoacyl‐CoA Synthases Drives Lipid Remodeling and Extreme Cold Adaptation in Antarctic <i>Pohlia nutans</i>

Antarctica's extreme cold challenges terrestrial life. In plants, β-ketoacyl-CoA synthase (KCS) is a critical enzyme for very long-chain fatty acids (VLCFAs) biosynthesis. However, the role of KCS genes in Antarctic mosses-the dominant terrestrial flora in this harsh ecosystem-remains poorly understood. Here, we performed a comparative analysis of cold tolerance and VLCFAs profiles between the Antarctic moss Pohlia nutans and the model bryophyte Physcomitrella patens, combined with functional characterization of the P. nutans KCS gene family (PnKCS1-19). P. nutans demonstrated superior growth rates and cold tolerance compared to P. patens. Furthermore, the PnKCS gene family has undergone substantial expansion via whole genome duplication, with intra-clade sequence homology exceeding 95.0%. Notably, heterologous expression of the PnKCS gene family in both wild-type and mutant yeast systems revealed novel VLCFAs profiles in some yeast strains, reflecting the distinct catalytic capabilities of PnKCSs. Heterologous of PnKCS7 and PnKCS8 in P. patens, which catalyzed the synthesis of a novel VLCFA component (C30:0) in wild yeast, enhanced the cold tolerance and total VLCFAs content of plant. These findings reveal the mechanism of Antarctic P. nutans adaptation via KCS-mediated VLCFAs synthesis, underscoring the ecological role of lipid remodeling.