Detection of large sequence insertions by a hybrid approach that combine de novo assembly and resequencing of medium-coverage genome sequences.

Large sequence insertion (LSI) is one of the structural variations (SVs) that may cause phenotypic differences in plants. To identify the LSIs using medium-coverage sequencing data of four wild soybean (Glycine soja) genotypes, we designed a hybrid approach combining de novo assembly and read mapping. Total reads and reads with both ends unmapped were independently assembled into "ordinary contigs" and "orphan contigs", respectively, and subjected to pairwise alignment and stringent filtering. This approach predicted 24 LSIs averaging 2682 bp in size, with no overlap with SVs detected by Pindel, BreakDancer, or ScanIndel, and they were validated by PCR. Compared with the soybean (Glycine max) reference genome, 20 LSIs were located outside genic regions. One of the four LSIs within a genic region, LSI05, is located in the coding DNA sequence region of a protein kinase superfamily gene (Glyma.08G123500). It caused delayed translation initiation and loss of 24 amino acids in the wild soybean genotype CW12. LSI05 was more frequently observed in 29 G. soja accessions than in 34 G. max accessions. Identified LSIs would be genomic resources harboring novel gene contents for studying SVs and improving crops. Moreover, our cost-efficient approach may be applicable to other plant species.