Chromosome-Level Genome Assembly of the Leafcutter Bee Megachile rotundata Reveals Its Ecological Adaptation and Pollination Biology.

The leafcutter bee Megachile rotundata is the world's most intensively managed solitary bee, owing to its easy manipulation and high pollination efficacy. Here, a high-quality chromosome-level M. rotundata genome, covering 280.68 Mb is presented. A total of 10 701 genes are predicted, of which 93.06% are functionally annotated. Based on the new genome assembly, transposable elements, noncoding RNAs, as well as gene families associated with pollination biology and ecological adaptation are systematically characterized. Comparative genomic analysis shows a notable expansion of Toll gene family but the contraction of detoxification gene in M. rotundata genome. Surprisingly, these expanded Toll-1 genes and their downstream genes display abundant mRNA levels in diapausing prepupae. Additionally, diapausing prepupae show significantly upregulated expression of antimicrobial peptide genes and a higher survival rate after Escherichia coli exposure compared to nondiapausing prepupae, indicating an enhanced immune response during M. rotundata diapause. The M. rotundata genome provides an important foundation for understanding its ecological adaptation and optimizing its exceptional pollination efficiency in the future.