Unified Multi-Caller Ensemble (UME) Generates an Unbiased Maize Haplotype Map for Variable Coverage Whole Genome Data

Area of Science:

• Genomics
• Plant Science
• Bioinformatics

Background:

• Developing a comprehensive maize (Zea mays ssp. mays) haplotype map (HapMap) is crucial for understanding genetic diversity.
• Existing methods face challenges with variable data coverage from diverse sources, leading to ascertainment bias.
• Minimizing bias is essential for accurate diversity studies in maize.

Purpose of the Study:

• To create a diversity-focused maize HapMap with over 64.5 million single nucleotide polymorphisms (SNPs).
• To introduce and validate a novel variant calling approach, Unified Multi-Caller Ensemble (UME), to address coverage biases.
• To provide a high-utility dataset for future maize genetic research and paleogenomic analyses.

Main Methods:

• Genotyping 818 diverse maize individuals, including landraces, inbred lines, and outgroups (Zea spp., Tripsacum spp.).
• Developing and implementing the Unified Multi-Caller Ensemble (UME) method to enhance variant calling accuracy in low- and mixed-coverage datasets.
• Employing a novel filtering strategy based on demographic signals to reduce sequencing errors while preserving genetic relationships.

Main Results:

• A comprehensive maize HapMap database was generated, featuring over 64.5 million SNPs and emphasizing landrace diversity.
• The UME method demonstrated superior performance in variant calling compared to individual callers, particularly for low-coverage samples.
• The resulting HapMap dataset is less affected by ascertainment bias, retaining full SNP diversity for broad utility.

Conclusions:

• The developed maize HapMap provides an unprecedented resource for studying genetic diversity, including paleogenomic analyses.
• The UME method effectively corrects for coverage biases, enabling accurate genotyping across diverse and challenging genomic datasets.
• This work facilitates a deeper understanding of maize natural diversity and supports future breeding efforts.