Effects of phylogeny and climate on seed oil fatty acid composition across 747 plant species in China

• We investigated the effects of phylogeny and climate on seed oil fatty acid composition.
• We tested how the degree of fatty acid unsaturation varies with climate.
• Phylogeny explains a higher proportion of variance in fatty acid composition.
• Fatty acid unsaturation may evolve as an adaptive strategy in colder climates.
• Phylogenetic and climate affiliations of fatty acids may help explore potential oil plants.

Seed oil has long been recognized as an important source of food, industry and biodiesel. In biological aspect, seed oil fatty acid composition (FAC) affects lipid fluidity and cellular metabolism, depending on temperature. Hence, the variation of FAC in seeds may reflect adaptive strategies for seed survival and seedling establishment under contrasting climate conditions. In this study, we investigated the relative effects of phylogeny and climate on seed oil FAC, testing the hypothesis that the degree of fatty acid unsaturation increases in colder climates. A large seed oil FAC dataset representing 747 species from 207 sites across China was compiled and a general linear model was used to partition total variance in FAC into taxonomic ranks (family, genus and species) and environmental components. Multiple regression analysis was conducted to examine the relative effects of mean annual temperature (MAT) and mean annual precipitation (MAP). Phylogenetically independent contrast (PIC) analysis was used to test the evolutionary association of FAC with climate at the family level. The results showed that seed oil FAC varied considerably across plant species, with phylogeny explaining a greater proportion of variance than environment; however, FAC showed obvious large-scale spatial patterns. Total unsaturated fatty acid (UFA) content increased with increasing latitude. The degree of fatty acid unsaturation, as indicated by the ratio of UFA to saturated fatty acids and iodine value, was negatively correlated with MAT and to a lesser extent with MAP. The PIC results indicated that at the family level, nearly all significant phenotypic correlations of FAC with spatial and climatic variables were evolutionarily convergent. These results indicate that despite strong phylogenetic constraints on FAC, fatty acid unsaturation in seed oil appears to evolve as an adaptive strategy in colder climates. The affiliation of phylogenetic and climate in seed oil FAC may assist in the search of potential oil plants with particular FAC for food and fuel needs.