Abstract: Triterpene scaffolds are cyclized by differential functional genes of the oxidosqualene cyclase (OSC) gene family, which are widely present in plant species. Thirty-nine OSCs were identified from the hexaploid bread wheat (Triticum aestivum L.) genome. The gene structure organization and the distribution of conserved motifs of OSCs gene family revealed that the TaOSC proteins are highly conserved. By phylogenetic analysis, all OSC proteins from wheat and other cereal crops were clustered into 11 subfamilies (I–XI). Based on the publicly available transcriptional profiling, the tissue-specific expression patterns of TaOSC during several developmental stages revealed diverged expression patterns, indicating that the TaOSC family has undergone subfunctionalization. Furthermore, homeolog expression bias was commonly detected in the TaOSC subfamilies, such as the expression of Ta5A004900 and Ta5D011800 in the subfamily II were specifically expressed in the leaf sheath and flag leaf sheath. In addition, two genes were strongly induced by Pst, indicating that the two homolog genes are involved in the resistance to powdery mildew. Molecular evolution analysis indicated that the TaOSC family genes were undergone purifying selection. So, the powdery mildew response may be very conservative and important biological function of the Ta5A004900 and Ta5D011800 in wheat. In conclusion, these results can be used to explore the diversity of triterpenes and clarify the mechanism of triterpene cyclization, and also provide useful information for future studies on the function of the TaOSC gene family in bread wheat and other important crops.

Key words: evolution, gene family, oxidosqualene cyclase, triterpene, wheat