Protoplast electrofusion between common wheat (Triticum aestivum L.) and Italian ryegrass (Lolium multiflorum Lam.) and regeneration of mature cybrids

Abstract

This study describes the development of electrofusion techniques using the ‘donor-recipient’ model for the production of cybrids between common cultivated winter wheat (Triticum aestivum L.) cv. Jinghua No. 1 and a phylogenetically remote, sexually incompatible grass species, Italian ryegrass (Lolium multiflorum Lam.), which belong to two different subtribes: Triticinae and Loliinae. Wheat protoplasts were metabolically inactivated by iodoacetamide before fusion, while protoplasts of Italian ryegrass were X-ray irradiated before protoplast isolation. The suspension cells were directly used to optizmize the inactivation parameters. By exploring the minimum irreversible membrane breakdown strength, the electrofusion parameters were optimized just a few minutes before electrofusion began. A total of 108 green plantlets were obtained, and about half of the green plants uncontrollably necrotized. Among all green plants, 14 were rooted normally and transplanted in growth chamber or field and developed to maturity. All these transplanted plants were male sterile with smaller and off-white anthers. Seeds were obtained by crossing with Jinghua No. 1. Three transplanted regenerants possessed the characteristics of glume facing the rachis, which was the taxonomic characteristic distinguishing the two subtribes of Triticinae and Lolliinae. Although Southern blot hybridization analysis of 33 randomly selected regenerants using a wheat ribosomal DNA probe (pHA71) did not find any differences to wheat, analysis using two mitochondrial probes B342 (cox l), 490 (Pro II) and one chloroplastidic probe pHve H5 revealed that 31 plants were ‘true cybrids’ by showing ryegrass-specific band(s) or new band(s). It also showed that the mitochondria and chloroplasts were not coexistent as the restriction fragment length polymorphism band of Italian ryegrass was not detected by the mitochondrial probes 7 (26s), B342 (cox I), pHJ2-7-1 (cox II), B30 (atp9), and the chloroplast probe pHvc P5. To regenerate the cybrids, the regeneration capacity of the recipient (wheat) was crucial in this study.