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Illustration of apomixis in wild type and engineering of asexual propagation through seeds based on the MiMe triple mutant. (A) In the wild type, the megaspore mother cell (MMC) undergoes meiosis, leading to the formation of reduced and recombined haploid (n) male and female gametes. Double fertilization of the egg cell and central cell by sperm cells leads to the formation of the embryo (2n) and endosperm (3n), respectively. (B) In the MiMe triple mutant, the MMC undergoes a mitotic-like division (mitosis instead of meiosis, MiMe), leading to the formation of unrecombined and unreduced diploid (2n) gametes. The fusion of the egg cell nucleus (2n) and central polar nucleus (4n) with the sperm cell nucleus (2n) produces a tetraploid (4n) clonal embryo and hexaploid (6n) endosperm, respectively. (C–E) Engineering apomixis has been achieved using three schemes based on the MiMe triple mutant. (C) Combination of the MiMe triple mutant with the ectopic expression of BBM (OsBBM1 in rice) in the egg cell triggers the formation of a parthenogenetic embryo (2n). (D) Crossing the male CENH3-modified genome elimination line (GEM) with the female MiMe triple mutant triggers the formation of a diploid clonal embryo (2n). (E) Creating the MiMe mtl quadruple mutant triggers the formation of a diploid clonal embryo (2n), but the ploidy of the endosperm is not known.
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In plants, embryogenesis and reproduction are not strictly dependent on fertilization. Several species can produce embryos in seeds asexually, a process known as apomixis. Apomixis is defined as clonal asexual reproduction through seeds, whereby the progeny is identical to the maternal genotype, and provides valuable opportunities for developing su...
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The combination of apomixis and hybrid production is hailed as the holy grail of agriculture for the ability of apomixis to fix heterosis of F1 hybrids in succeeding generations, thereby eliminating the need for repeated crosses to produce F1 hybrids. Apomixis, asexual reproduction through seed, achieves this feat by circumventing two processes tha...
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... Apomixis produces offspring without sperm-egg interaction and was first discovered by Smith in Aconitum [1], and have been described in more than 400 flower plant species. Thus far, the majority of research on apomixis has been conducted on Hieracium umbellatum L., Tripsacum L., Arabidopsis thaliana and other related wild species [2]. ...
Apomixis is a unique reproductive process that produces fertile offspring without the combination of sperm and egg cells. This process perfectly reproduces maternal DNA, making it possible to fix heterosis during reproduction. Malus shizongensis is a newly discovered species that is closely related to Malus hupehensis Rehd. After de-male bagging, it was found that the fruit set rate reached 78.7%. Preliminary analysis indicated that M. shizongensis have apomictic reproductive characteristics. In this work, we employed paraffin sectioning and electron scanning microscopy to explore apomixis in M. shizongensis during the development of male–female gametes and embryo sacs. Stigma fluorescence assays showed that pollen germination was normal, but less pollen entered the ovaries. Additionally, analysis of anthers indicated the presence of dysplasia and paraffin sectioning revealed that the pollen mother cells were aborted due to abnormal disintegration of the tapetum layer. Taken together, our results indicate that the primary causes of apomixis in M. shizongensis are anther dysplasia and male gamete development failure, resulting in reduced pollen tube entry into ovaries and reduced reproduction of female gametes. In conclusion, this study provide a theoretical basis and technical supports for apple stock breeding and apple industry development.
... X. . In the SE process, somatic embryos are produced either directly from differentiated somatic cells or indirectly via embryogenic callus (EC; Su et al., 2021;Yin et al., 2022). Owing to these features, SE has found widespread uses in a variety of contexts, including but not limited to, germplasm conservation, artificial seed production, haploid breeding, asexual reproduction, and as a platform tool in the research field of plant biotechnology. ...
Plant somatic embryogenesis (SE) is a multifactorial developmental process where embryos that can develop into whole plants are produced from somatic cells rather than through the fusion of gametes. The molecular regulation of plant SE, which involves the fate transition of somatic cells into embryogenic cells, is intriguing yet remains elusive.
We deciphered the molecular mechanisms by which GhRCD1 interacts with GhMYC3 to regulate cell fate transitions during SE in cotton. While silencing of GhMYC3 had no discernible effect on SE, its overexpression accelerated callus formation, and proliferation.
We identified two of GhMYC3 downstream SE regulators, GhMYB44 and GhLBD18. GhMYB44 overexpression was unconducive to callus growth but bolstered EC differentiation. However, GhLBD18 can be triggered by GhMYC3 but inhibited by GhMYB44, which positively regulates callus growth. On top of the regulatory cascade, GhRCD1 antagonistically interacts with GhMYC3 to inhibit the transcriptional function of GhMYC3 on GhMYB44 and GhLBD18, whereby a CRISPR‐mediated rcd1 mutation expedites cell fate transition, resembling the effects of GhMYC3 overexpression. Furthermore, we showed that reactive oxygen species (ROS) are involved in SE regulation.
Our findings elucidated that SE homeostasis is maintained by the tetrapartite module, GhRCD1–GhMYC3–GhMYB44–GhLBD18, which acts to modulate intracellular ROS in a temporal manner.
... Despite the recent advances in synthetic apomixis in monocots such as rice, the process is still poorly explored in maize, in which efforts are more focused in the development of haploid induction. Apomixis-based genome editing strategies can be exploited to directly edit hybrids, fix hybrid vigor and facilitate clonal propagation of GE lines, although they need to be further optimized to be vastly applied in hybrid seed production in various crops (recently reviewed by Ozias-Akins and Conner 2020; Chen et al., 2021;Yin et al., 2022). ...
Recent advances in genome editing have enormously enhanced the effort to develop biotechnology crops for more sustainable food production. CRISPR/Cas, the most versatile genome-editing tool, has shown the potential to create genome modifications that range from gene knockout and gene expression pattern modulations to allele-specific changes in order to design superior genotypes harboring multiple improved agronomic traits. However, a frequent bottleneck is the delivery of CRISPR/Cas to crops that are less amenable to transformation and regeneration. Several technologies have recently been proposed to overcome transformation recalcitrance, including HI-Edit/IMGE and ectopic/transient expression of genes encoding morphogenic regulators. These technologies allow the eroding of the barriers that make crops inaccessible for genome editing. In this review, we discuss the advances in genome editing in crops with a particular focus on the use of technologies to improve complex traits such as water use efficiency, drought stress, and yield in maize.
... Spontaneous haploids are observed in nature and can develop in the following ways: (1) semigamy (an abnormal type of fertilization whereby either reduced or unreduced male and female gametes participate in embryo formation, but fertilization does not occur); (2) polyembryony (the production of two or more embryos in one seed, owing to the existence and fertilization of more than one embryonic sac in one ovule); (3) androgenesis (embryo formation after failure of the egg nucleus to participate in fertilization); or (4) gynogenesis (embryo formation after failure of the sperm cell to fuse with the egg nucleus). However, the occurrence of spontaneous haploidization is rare [9,10]. On the other hand, haploids can be induced by various in vitro methods using female and male gametophytes ( Figure 1). ...
The induction of haploid cell development into normal plants enables the production of doubled haploid lines, which are homozygous and can be used in breeding programs as an alternative to conventionally derived inbred lines. In this paper, we present the historical background and current status of the attempts of haploid induction in carrot (Daucus carota L.). Economically, carrot is one of the most important vegetables. It is an outcrossing diploid (2n = 2x = 18) species. Nowadays, the seeds of hybrid cultivars constitute the majority of the carrot seeds sold in the world. Hybrid cultivars of carrot are produced using inbred populations. Inbreeding in this species is difficult due to an inbreeding depression and is also time-consuming, as it is a biennial crop. Therefore, the implementation of the haploidization technology into the breeding programs of carrot is of high interest. Androgenesis, gynogenesis and induced parthenogenesis are the methods that have been used for haploid induction, and their potential in haploidization of carrot is discussed. The centromere-specific histone 3 variant (CENH3) and its manipulation in carrot is also acknowledged.
... In three separate development, CRISPR/Cas9-mediated genome editing was used to synchronously knockout three genes in rice, PAIR1, OsREC8, and OsOSD1 (Khanday et al., 2019), OsSPO11-1, OsREC8, and OsOSD1 (Xie et al., 2019) and OSD1, SPO11/PAIR1 and REC8 (Muliet et al., 2016). A common limitation of these reports are the efficiency of seed production and paucity of pathogenesis thus additional parthenogenesis or an inducer without fertilization is needed for MiMe phenotypes to achieve apomixis and resolve the issue of low fertility(Yin et al., 2022). Specific expression of BBM and MATL genes promotes the elimination of the paternal genome after fertilization whereas editing of BBM1 expression or disruption of MTL leads to clonal seed production and heritability for multiple generations. ...
Genome editing offers a range of solutions for more efficient development of crops that are productive, adapted to stresses, climate-resilient, and less dependent on agro-inputs. Clustered regularly interspaced short palindromic repeats (CRISPR)–CRISPR-associated protein (Cas9) technology is the current dominant tool used for genome editing. Originally, a Cas9 nuclease was employed to induce a double-strand break in its target site, causing the deletion of a few base pairs, inversion and gene integration to deliver desired changes in organisms. Aside from the primary nuclease activity (knock-in/out), a Base editor system, Gene priming and Cargo chauffeuring activities have been reported to deliver functionalities to specific regions in the DNA such as regulating transcription and fluorescence DNA for visualizing and understanding biological systems. Limitations of the scope of Cas9 activity were also eliminated by the recent development of more Cas9 orthologues (Cpf1-RR and Cpf1-RVR). Cas9 together with the advent of novel base editing tools that enable precise genome modifications and DNA-free genome editing via ribonucleoproteins demonstrate significant promise in the development of future crop improvement strategies. However, large-scale adoption of CRISPR/CAS will require optimizing strategies while accounting for costs, ease of implementation, and potential impacts on production gains. This review focuses on CRISPR application in plants, advances in CRISPR technology, regulations that may disadvantage scientists, resources for the smooth application of CRISPR and the preparedness of Africa to benefit from CRISPR technology.
... Apomixis, a form of reproduction, is de ned as asexual reproduction through seeds (Palumbo et al. 2022; Underwood and Mercier 2022; Yin et al. 2022). Since embryos are produced without meiosis, genetic makeup of apomictic progenies is identical to that of mother plants. ...
Nucellar embryony, a form of apomixis, is one of the most important traits in citrus breeding. Transposition of a miniature inverted repeat transposable element (MITE) in the promoter of CitRWP gene has been previously reported as the causal mutation. However, features of the MITE such as sequences of terminal inverted repeats (TIRs) and target site duplications (TSDs) remain unclear. An MITE family, DTM10, showing the highest homology was identified from 110 citrus MITE families. At least 80 DTM10 elements were identified from each of 10 genome sequences of Citrinae species. Analysis of 114 sweet orange elements showed that DTM10 contained 56-bp TIRs and mostly 9-bp TSDs. Phylogenetic analyses of DTM10 elements identified from five Citrinae species showed that MITEs in CitRWP might have transposed in a common ancestor of Citrus species. Two inverted MITEs were identified from three mutant alleles analyzed. In addition, three tandem MITEs were identified in the mutant allele of Fortunella CitRWP . A strong DNA secondary structure formed between MITEs was predicted. Due to a strong stem-loop structure, a phenomenon of polymerase jumping was observed during PCR amplification. To develop reliable molecular markers, sequences of mutant and wild-type CitRWP alleles were obtained from diverse citrus accessions. Phylogenetic analysis of CitRWP alleles showed that mutant alleles might have originated from a common ancestor of Citrus species. Based on MITE insertion and a single nucleotide polymorphism in the genic region, three complementary molecular markers were developed. Genotyping results of 241 citrus accessions were found to be identical among three molecular markers.
