Genetic analysis of mitochondrial sorting from the MSC3 mosaic mutant of cucumber

Authors: Wallace, Lyle; Havey, Michael

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2021
Publication Date: 7/6/2021
Citation: Wallace, L.T., Havey, M.J. 2021. Genetic analysis of mitochondrial sorting from the MSC3 mosaic mutant of cucumber. Journal of the American Society for Horticultural Science. 146(5):346-350. https://doi.org/10.21273/JASHS05075-21.
DOI: https://doi.org/10.21273/JASHS05075-21

Interpretive Summary: Passage of the highly inbred line ‘B’ of cucumber through cell cultures produces plants with a mosaic (MSC) phenotype on cotyledons and leaves, as well as rearrangements in the mitochondrial DNA. Both of these characteristics show paternal transmission. MSC3 and MSC16 were derived from different cell-culture experients and have distinct mosaic phenotypes and different under-represented regions in their mitochondrial DNAs. A nuclear locus, Psm for paternal transmission of mitochondria, conditions a high proportion of wild type progenies when MSC16 is crossed as the male with female plants carrying the Psm- allele. Plants with homozygous genotypes at Psm were crossed with both MSC3 and MSC16, and segregation of wild-type versus mosaic progenies in these families were not consistent suggesting that sorting of wild-type progenies from crosses with MSC3 and MSC16 have different genetic bases. We identified cucumber plants that produced a high proportion of wild-type progenies in crosses with MSC3 as the male parent. Plants from a segregating F2 family were crossed with MSC3 as the male and progenies scored for numbers of mosaic versus wild-type progenies. The same F2 plants were genotyped-by-sequencing and single nucleotide polymorphisms identified for genetic mapping. Quantitative analysis of the proportion of wild-type progenies identified a major quantitative trait locus (QTL) in the same genomic region as the Psm locus; however the most significant SNP associated with this QTL was located over 856 kilobases from Psm. Eventual identification of a candidate gene controlling this mitochondrial sorting in cucumber should reveal important aspects of mitochondrial-nuclear interactions affecting the prevalence of specific mitochondrial DNAs. This research will be useful for cucurbit breeders towards exploitation of beneficial nuclear-mitochondrial interactions to enhance productivity.

Technical Abstract: Passage of the highly inbred line ‘B’ of cucumber through cell cultures has produced regenerated plants with a mosaic (MSC) phenotype on cotyledons and leaves, as well as rearrangements in the mitochondrial DNA. Both of these characteristics show paternal transmission. MSC3 and MSC16 were derived from independent cell-culture experients and have distinct mosaic phenotypes and different under-represented regions in their mitochondrial DNAs. A nuclear locus, Psm for paternal transmission of mitochondria, conditions a high proportion of wild type progenies when MSC16 is crossed as the male with female plants carrying the Psm- allele. Plants with homozygous genotypes at Psm were crossed with both MSC3 and MSC16, and segregation of wild-type versus mosaic progenies in these families were not consistent suggesting that sorting of wild-type progenies from crosses with MSC3 and MSC16 have different genetic bases. We identified cucumber plants that produced a high proportion of wild-type progenies in crosses with MSC3 as the male parent. Plants from a segregating F2 family were crossed with MSC3 as the male and progenies scored for numbers of mosaic versus wild-type progenies. The same F2 plants were genotyped-by-sequencing and single nucleotide polymorphisms identified for genetic mapping. Quantitative analysis of the proportion of wild-type testcross progenies identified a major quantitative trait locus (QTL) in the same genomic region as the Psm locus; however the most significant SNP associated with this QTL was located over 856 kilobases from Psm. Eventual identification of a candidate gene controlling this mitochondrial sorting in cucumber should reveal important aspects of mitochondrial-nuclear interactions affecting the prevalence of specific mitochondrial DNAs.