Abstract
Apomixis is a method of reproduction to generate clonal seeds and offers tremendous potential to fix heterozygosity and hybrid vigor. The process of apomictic seed development is complex and comprises three distinct components, viz., apomeiosis (leading to formation of unreduced egg cell), parthenogenesis (development of embryo without fertilization) and functional endosperm development. Recently, in many crops, these three components are reported to be uncoupled leading to their partitioning. This review provides insight into the recent status of our understanding surrounding partitioning apomixis components in gametophytic apomictic plants and research avenues that it offers to help understand the biology of apomixis. Possible consequences leading to diversity in seed developmental pathways, resources to understand apomixis, inheritance and identification of candidate gene(s) for partitioned components, as well as contribution towards creation of variability are all discussed. The potential of Panicum maximum, an aposporous crop, is also discussed as a model crop to study partitioning principle and effects. Modifications in cytogenetic status, as well as endosperm imprinting effects arising due to partitioning effects, opens up new opportunities to understand and utilize apomixis components, especially towards synthesizing apomixis in crops.
Highlights
Overview of Apomixis Phenomenon: Genetics and RegulationApomixis is a natural method of clonal reproduction through seeds, whereby the progeny is represented exactly by the maternal genotype (Asker and Jerling, 1992)
Induction of autonomous mode of endosperm development in otherwise pseudogamous species by acquiring additional genetic determinants or by removal of suppressors that restrict the proliferation of polar nuclei in absence of fertilization, or vice versa
Such modifications are reported in several apomictic species (e.g., Taraxacum officinale, Panicum maximum, Hieracium spp., etc.) and in mutants mimicking apomixis components in otherwise sexual crops
Summary
Apomixis is a natural method of clonal reproduction through seeds, whereby the progeny is represented exactly by the maternal genotype (Asker and Jerling, 1992). As a consequence of uncoupling of apomixis components, the functional linkage between apomeiosis and parthenogenesis is lost, and apomeiotically derived unreduced egg cell (2n) loses the capacity of parthenogenesis and requires fertilization with male gamete (1n) for embryo development, eventually leading to the formation of a triploid embryo (2n + 1n = 3n) This recombined pathway may be represented as apomeiosis:zygotic-embryogenesis. Induction of autonomous mode of endosperm development in otherwise pseudogamous species by acquiring additional genetic determinants or by removal of suppressors that restrict the proliferation of polar nuclei in absence of fertilization, or vice versa Such modifications are reported in several apomictic species (e.g., Taraxacum officinale, Panicum maximum, Hieracium spp., etc.) and in mutants mimicking apomixis components in otherwise sexual crops (van Dijk et al, 2003; Bicknell and Koltunow, 2004; Kaushal et al, 2008; Schmidt et al, 2015; Brukhin, 2017). The situation may be more complex in facultative individuals, as both sexual and apomeiotic factors are present in the same genotype, though with different extensions (Delgado et al, 2016; Kaushal et al, 2018)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
