#androgenesis

Plant tissue culture 2

Plants produced via androgenesis are initially:

Plants produced via androgenesis are initially haploid bearing single chromosome set n derived from meiotic reduction of diploid mother cells into microspores. After meiosis each microspore contains recombined haploid genome; when cultured without fertilization embryogenic divisions maintain this n number, so tissues leaves roots show halved DNA content compared to diploid control confirmed by flow cytometry and chromosome counting revealing for example 7 chromosomes in barley haploid versus 14 diploid. Such haploids exhibit reduced vigor smaller organs small stomatal guard cells and complete male and female sterility due to failure of homologous pairing during meiosis producing unbalanced gametes. For breeding utility spontaneous or induced chromosome doubling restores diploidy creating doubled haploid line homozygous at all loci capturing single meiotic recombination event. Spontaneous doubling occurs at low frequency through endomitosis nuclear fusion, but artificial doubling usually applied using colchicine or oryzalin which inhibit spindle fiber polymerization during mitosis causing chromosome duplication without cell division. Haploid phase is prerequisite step linking gametic selection to instant homozygous diploid production accelerating cultivar development.

Ref: Kasha & Kao 1970 haploid plants; Maluszynski et al., FAO doubled haploid manual.

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Plant tissue culture 2

Gynogenesis differs from androgenesis because it uses:

Gynogenesis differs from androgenesis because it uses female gametophyte components unfertilized ovules ovaries or embryo sacs as explant source rather than anther pollen. In gynogenesis egg cell synergid or antipodal cells within embryo sac are induced to develop sporophytically into haploid embryo without fertilization, typically by culturing unpollinated ovaries or ovules on sucrose enriched medium with auxin cytokinin combination. Female gametophyte origin ensures captured genome is that of maternal parent, contrasting with androgenesis capturing paternal genome from microspores. Gynogenesis became important in crops where androgenesis is recalcitrant or produces high frequency of albino plantlets such as sugar beet onion cucumber barley where pollen culture fails. Culture conditions differ often requiring high sucrose 8-10 percent to mimic ovary environment and dark incubation initially. Induction rate generally lower than androgenesis but avoids genotype dependent albinism. Both pathways converge on production of haploid plants that are initially sterile n and require colchicine mediated chromosome doubling to generate doubled haploid lines fully homozygous valuable for hybrid breeding and marker assisted selection programs.

Ref: Yang & Zhou Theor Appl Genet gynogenesis; Bohanec 2009 haploid production review.

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Plant tissue culture 2

Androgenesis is commonly achieved by culture of:

Androgenesis is commonly accomplished through culture of anthers or isolated microspores pollen at uninucleate stage, landmark discovery by Guha and Maheshwari 1964 in Datura innoxia demonstrating that anthers could produce haploid embryos on MS medium. Most responsive microspores are at mid uninucleate to early binucleate stage where gametophytic commitment is still reversible; vacuolate microspores have large central vacuole and peripheral nucleus poised for embryogenic switch. Anthers excised from surface sterilized buds given cold pretreatment 4 degrees for several days or heat shock 33 degrees that disrupts cytoskeleton and blocks starch accumulation are placed on agar solidified medium containing auxin 2,4-D and cytokinin BAP at low levels plus sucrose 3 percent often with activated charcoal adsorbing inhibitory phenolics from anther wall. Inside locule microspores undergo sporophytic divisions forming multicellular structures that rupture exine to emerge as globular embryos. Isolated microspore culture eliminates anther wall somatic tissue producing higher haploid yield and better for transformation but requires precise density control 10^4 per ml and nurse culture. Ovule culture corresponds to gynogenesis not androgenesis.

Ref: Nitsch & Nitsch 1969 androgenesis; Germaná 2011 anther culture history; NCBI NBK21429.

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Plant tissue culture 2

Androgenesis results in plants genetically identical to:

Androgenesis results in plants whose nuclear genetic constitution is identical to male parent gamete contribution because development originates from male gametophyte microspore. Microspores formed after meiosis in anther tapetum carry recombined haploid genome representing segregation products of diploid male parent heterozygous loci. Under stress pretreatment cold starvation heat and culture conditions gametophytic program that would normally produce mature binucleate pollen with vegetative generative cells is aborted, sporophytic pathway triggered leading to repeated mitotic divisions forming embryoid or callus inside anther locule. Since no contribution from female genome occurs, regenerated plant inherits solely paternal alleles for nuclear traits such as disease resistance plant height etcetera, while organellar DNA may show biparental leakage depending on species. Initially plants are haploid n requiring chromosome doubling via colchicine to restore diploidy producing doubled haploids fully homozygous for male derived alleles. This feature enables capture of male recombination products in single generation accelerating breeding for traits transmitted through pollen parent without maternal interference.

Ref: Guha & Maheshwari 1964 androgenesis; Touraev et al., Trends Plant Sci microspore embryogenesis.

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Plant Breeding 4

Androgenesis involves culture of:

Androgenesis is male gametophyte-mediated haploid production pathway exploiting totipotency of immature pollen. Anthers containing uninucleate microspores at late uninucleate to early binucleate stage are excised and cultured on nutrient media, or isolated microspores are separated from anthers and cultured in liquid medium under stress. Developmental program of microspore shifts from pollen grain maturation toward sporophytic division, forming embryo-like structures or callus that regenerate haploid plantlets with n chromosomes derived entirely from paternal gametic genotype. Process exploits ability to switch from gametophytic to embryogenic pathway under stress treatments such as cold pretreatment, starvation, heat shock, and hormones auxin and cytokinin. Androgenic DH lines have been successful in rice, wheat, barley, tobacco, and pepper. Efficiency depends on genotype responsiveness, microspore stage precision, and anther wall influence, requiring optimization of media with sucrose and growth regulators for embryo induction and regeneration protocols. Androgenic response is regulated by embryogenic genes BBM, LEC1, SERK, and chromatin remodeling factors; stress induced reprogramming involves histone deacetylation, DNA demethylation, and auxin biosynthesis shift, converting microspore from gametophytic to sporophytic fate enabling efficient haploid embryo formation in responsive genotypes under optimized protocols.

Ref: Seguí-Simarro JM. Androgenesis review 2010 J Exp Bot; Maluszynski et al. FAO Haploid protocols – anther culture

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