The ancestral tomato species are known to possess genes that are valuable for improving traits in breeding. Here, we aimed to construct high-quality de novo genome assemblies of Solanum pimpinellifolium ‘LA1670’ and S. lycopersicum var. cerasiforme ‘LA1673’, originating from Peru. The Pacific Biosciences (PacBio) long-read sequences with 110× and 104× coverages were assembled and polished to generate 244 and 202 contigs spanning 808.8 Mbp for ‘LA1670’ and 804.5 Mbp for ‘LA1673’, respectively. After chromosome-level scaffolding with reference guiding, 14 scaffold sequences corresponding to 12 tomato chromosomes and 2 unassigned sequences were constructed. High-quality genome assemblies were confirmed using the Benchmarking Universal Single-Copy Orthologs and long terminal repeat assembly index. The protein-coding sequences were then predicted, and their transcriptomes were confirmed. The de novo assembled genomes of S. pimpinellifolium and S. lycopersicum var. cerasiforme were predicted to have 71,945 and 75,230 protein-coding genes, including 29,629 and 29,185 non-redundant genes, respectively, as supported by the transcriptome analysis results. The chromosome-level genome assemblies coupled with transcriptome data sets of the two accessions would be valuable for gaining insights into tomato domestication and understanding genome-scale breeding.

mitoTALEN, a mitochondrial genome editing technology, demonstrated that the mitochondrial gene orf137 is responsible for inducing cytoplasmic male sterility in tomato.

To identify cytoplasmic male sterility (CMS)-associated genes in tomato, we determined the genome sequences of mitochondria and chloroplasts in three CMS tomato lines derived from independent asymmetric cell fusions, their nuclear and cytoplasmic donors, and male fertile weedy cultivated tomato and wild relatives. The structures of the CMS mitochondrial genomes were highly divergent from those of the nuclear and cytoplasmic donors, and genes of the donors were mixed up in these genomes. On the other hand, the structures of CMS chloroplast genomes were moderately conserved across the donors, but CMS chloroplast genes were unexpectedly likely derived from the nuclear donors. Comparative analysis of the structures and contents of organelle genes and transcriptome analysis identified three genes that were uniquely present in the CMS lines, but not in the donor or fertile lines. RNA-sequencing analysis indicated that these three genes transcriptionally expressed in anther, and identified different RNA editing levels in one gene, orf265, that was partially similar to ATP synthase subunit 8, between fertile and sterile lines. The orf265 was a highly potential candidate for CMS-associated gene. This study suggests that organelle reorganization mechanisms after cell fusion events differ between mitochondria and chloroplasts, and provides insight into the development of new F1 hybrid breeding programs employing the CMS system in tomato.

To identify cytoplasmic male sterility (CMS)-associated genes in tomato, we determined the genome sequences of mitochondria and chloroplasts in three CMS tomato lines derived from independent asymmetric cell fusions, their nuclear and cytoplasmic donors, and male fertile weedy cultivated tomato and wild relatives. The structures of the CMS mitochondrial genomes were highly divergent from those of the nuclear and cytoplasmic donors, and genes of the donors were mixed up in these genomes. On the other hand, the structures of CMS chloroplast genomes were moderately conserved across the donors, but CMS chloroplast genes were unexpectedly likely derived from the nuclear donors. Comparative analysis of the structures and contents of organelle genes and transcriptome analysis identified three genes that were uniquely present in the CMS lines, but not in the donor or fertile lines. RNA sequencing analysis indicated that these three genes transcriptionally expressed in anther, two of which were also expressed in pollen. They could be potential candidates for CMS-associated genes. This study suggests that organelle reorganization mechanisms after cell fusion events differ between mitochondria and chloroplasts, and provides insight into the development of new F1 hybrid breeding programs employing the CMS system in tomato.