Effects of p-chlorophenoxyisobutyric acid, arabinogalactan, and activated charcoal on microspore embryogenesis in kale

Suberoylanilide hydroxamic acid induced microspore embryogenesis and promoted plantlet regeneration in ornamental kale (Brassica oleracea var. acephala)

Isolated Microspore Culture (IMC) is an efficient method to obtain the homozygous strain; however, it is difficult to apply in ornamental kale due to its low rate of microspore embryogenesis. Histone acetylation is an important epigenetic mechanism and may affect the changes of the microspore development pathway, promoting microspore embryogenesis. Here, microspores from three cut-flower ornamental kales, namely Crane Feather Queen (CFQ), Crane Pink (CP), and Crane Bicolor (CB), were treated with the histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) to induce embryogenesis. The haploid 'CFQ' microspore plantlets were doubled with colchicine. The results for 'CFQ' revealed that, the appropriate concentration of SAHA was 0.03 μM and obtained 17.27 embryos per bud. For 'CP,' the appropriate concentration of SAHA was 0.045 μM and obtained 11.19 embryos per bud. For 'CB,' the appropriate concentration of SAHA was 0.045 μM and obtained 6.10 embryos per bud. Haploid 'CFQ' microspore plantlets were treated with 75 mg/L colchicine for 7 d and the doubling rate was 41.7%. Haploid 'CFQ' plantlets were treated with 1000 mg/L colchicine by root-soaking for 4 h and the doubling rate was 64.3%. SAHA could promote microspore embryogenesis, and colchicine root soaking was more effective than adding colchicine to the medium for haploid plantlet doubling in cut-flower ornamental kale.

Androgenesis-Based Doubled Haploidy: Past, Present, and Future Perspectives

Androgenesis, which entails cell fate redirection within the microgametophyte, is employed widely for genetic gain in plant breeding programs. Moreover, androgenesis-responsive species provide tractable systems for studying cell cycle regulation, meiotic recombination, and apozygotic embryogenesis within plant cells. Past research on androgenesis has focused on protocol development with emphasis on temperature pretreatments of donor plants or floral buds, and tissue culture optimization because androgenesis has different nutritional requirements than somatic embryogenesis. Protocol development for new species and genotypes within responsive species continues to the present day, but slowly. There is more focus presently on understanding how protocols work in order to extend them to additional genotypes and species. Transcriptomic and epigenetic analyses of induced microspores have revealed some of the cellular and molecular responses required for or associated with androgenesis. For example, microRNAs appear to regulate early microspore responses to external stimuli; trichostatin-A, a histone deacetylase inhibitor, acts as an epigenetic additive; ά-phytosulfokine, a five amino acid sulfated peptide, promotes androgenesis in some species. Additionally, present work on gene transfer and genome editing in microspores suggest that future endeavors will likely incorporate greater precision with the genetic composition of microspores used in doubled haploid breeding, thus likely to realize a greater impact on crop improvement. In this review, we evaluate basic breeding applications of androgenesis, explore the utility of genomics and gene editing technologies for protocol development, and provide considerations to overcome genotype specificity and morphogenic recalcitrance in non-model plant systems.