Genetic Mapping of Mitochondrial Sorting of the MSC3 Mosaic Mutant of Cucumber

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 experiments 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 approximately 856 kilobases from Psm. Eventual identification of a candidate gene controlling this unique mitochondrial sorting in cucumber should reveal important aspects of mitochondrial-nuclear interactions affecting the prevalence of specific mitochondrial DNAs.

Trans-Generational Impacts of Paternal Irradiation in a Cricket: Damage, Life-History Features and Hormesis in F1 Offspring

Animals exposed to significant stress express multi-modal responses to buffer negative impacts. Trans-generational impacts have been mainly studied in maternal lines, with paternal lines having received less attention. Here, we assessed paternal generational effects using irradiated male crickets ( Acheta domesticus), and their F1 offspring (irradiated males mated to unirradiated females). Paternal transmission of radiation impacts emerged in multiple life history traits when compared to controls. Irradiated males and their F1 offspring expressed hormetic responses in survivorship and median longevity at mid-range doses. For F0 males, 7 Gy & 10 Gy doses extended F0 longevity by 39% and 34.2% respectively. F1 offspring of 7 Gy and 10 Gy sires had median lifespans 71.3% and 110.9% longer, respectively. Survivorship for both F0 7 Gy (p < 0.0001) and 10 Gy (p = 0.0055) males and F1 7 Gy and 10 Gy (p < 0.0001) offspring significantly surpassed that of controls. Irradiated F0 males and F1 offspring had significantly reduced growth rates. For F0 males, significant reductions were evident in 4Gy-12 Gy males and F1 offspring in 4 Gy (p < 0.0001), 7 Gy (p < 0.0001), and 10 Gy (p = 0.017). Our results indicate paternal effects; that irradiation directly impacted males but also mediated diverse alterations in the life history features (particularly longevity and survivorship) of F1 offspring.