Expression of nuclear-cytoplasmic genomic incompatibility in interspecific Petunia somatic hybrid plants

Abstract

Somatic hybrid plants were regenerated following calcium-high pH fusion of the unidirectional, sexually incompatible cross of Petunia parodii wild-type leaf mesophyll protoplasts with protoplasts from a cytoplasmic determined chlorophyll-deficient mutant of P. inflata. Genic complementation to chlorophyll synthesis and sustained growth in the selective medium was used to visually identify hybrid calluses. Hybrid calluses were subsequently regenerated to shoots, rooted, and confirmed as somatic hybrids by their intermediate floral and leaf morphology based on comparison to the 2 n = 4 x = 28 sexual counterpart, dominant anthocyanin expression in the corolla, chromosome number, and peroxidase and maleic dehydrogenase isozyme patterns. Certain cytologically stable somatic hybrids displayed aberrant reproductive and floral morphologies including subtle to moderate corolla and leaf pigment variegation, floral dimension changes and reduced pollen viability. In contrast, cytologically unstable somatic hybrids showed various degrees of aneuploidy coupled with corolla splitting, and irregularities in reproductive organs such as double stigmas and styles in addition to reduced pollen viability. Postulated mechanisms to account for these phenotypic changes in stable and unstable somatic hybrids include nuclear-cytoplasmic genomic incompatibility, chromosome loss in a biparental cytoplasm, or a phenomenon similar to hybrid dysgenesis occurring as a result of somatic fusion.

Somatic versus sexual hybridization: features, facts and future

“…Aberrant traits resulting from the process of hybrid disgenesis, such as sterility, segregation and sex ratio distortions, high frequency mutations, chromosome structural changes, rearrangement and nondisjunction, split corolla phenotype and variegation, have been observed in specific hybrid combinations and are conditioned by the direction of the cross in both plants (e.g. Oenothera, Petunia) and Drosophila (D'Amato 1977;Schnabelraum et al 1985, and references therein).…”

“…Somatic interspecific hybrids show, as their sexual counterparts do, low or no selffertility (Hamill et al 1985;Schnabelraum et al 1985;O'Connell & Hanson 1987;Sundberg et al 1987;Sidorov et al 1987;Wright et al 1987). By recurrent selection of the most fertile individuals over two generations it was possible to increase the level of self-fertility in Nicotiana hybrids (Hamill et al 1985).…”

“…By recurrent selection of the most fertile individuals over two generations it was possible to increase the level of self-fertility in Nicotiana hybrids (Hamill et al 1985). In Petunia (Schnabelraum et al 1985), the sexual cross of P. parodii x P. inflata was successful only with P. parodii as the female partner (prezygotic incompatibility), while in the somatic hybrids dysgenic mechanisms were considered to operate.…”

Production of fertile somatic hybrid plants between Oriental hybrid lily and Lilium�formolongi

“…In the case of floricultural crops, reports of protoplast-to-plant systems have accumulated for Petunia (reviewed in Sink 1991), which belongs to the Solanaceae family, and further investigations based on the protoplast-to-plant system have been actively carried out, especially on the symmetric/asymmetric somatic hybridization for the improvement of floricultural crops (Power et al 1978(Power et al , 1979(Power et al , 1980Schnabelrauch et al 1985;Taguchi et al 1993) and for the analysis of genomic rearrangements (Clark et al 1986;Bonnett and Glimelius 1990;Hinnisdaels et al 1991). Though several studies have succeeded in regenerating commercially important floricultural crops from protoplasts, such as Dianthus (reviewed in Nakano and Mii 1995), Rosa (Matthews et al 1991), Chrysanthemum (Lindsay and Ledger 1993), and Iris (Shimizu et al 1996), reports of successful somatic hybridization have, to the best of our knowledge, been limited (Shimizu et al 1999;reviewed in Nakano et al 2001).…”

Petunia

“…parodii + P. integrifolia subsp. inflata somatic hybrids were not as stable as their sexually produced counterparts (Schnabelrauch et al, 1985). Many of the plants produced branches with slightly abnormal leaves and flowers.…”