The Genetic Control of Apomixis: Asexual Seed Formation

Abstract

Apomixis (asexual seed formation) is the result of a plant gaining the ability to bypass the most fundamental aspects of sexual reproduction: meiosis and fertilization. Without the need for male fertilization, the resulting seed germinates a plant that develops as a maternal clone. This dramatic shift in reproductive process has been documented in many flowering plant species, although no major seed crops have been shown to be capable of apomixis. The ability to generate maternal clones and therefore rapidly fix desirable genotypes in crop species could accelerate agricultural breeding strategies. The potential of apomixis as a nextgeneration breeding technology has contributed to increasing interest in the mechanisms controlling apomixis. In this review, we discuss the progress made toward understanding the genetic and molecular control of apomixis. Research is currently focused on two fronts. One aims to identify and characterize genes causing apomixis in apomictic species that have been developed as model species. The other aims to engineer or switch the sexual seed formation pathway in non-apomictic species, to one that mimics apomixis. Here we describe the major apomictic mechanisms and update knowledge concerning the loci that control them, in addition to presenting candidate genes that may be used as tools for switching the sexual pathway to an apomictic mode of reproduction in crops.

A parthenogenesis gene of apomict origin elicits embryo formation from unfertilized eggs in a sexual plant

“…In this study, we demonstrate that the PsASGR-BABY BOOM-like (PsASGR-BBML) gene is expressed in egg cells before fertilization and can induce parthenogenesis and the production of haploid offspring in transgenic sexual pearl millet. A reduction of PsASGR-BBML expression in apomictic F 1 RNAi transgenic plants results in fewer visible parthenogenetic embryos and a reduction of embryo cell number compared with controls. Our results endorse a key role for PsASGR-BBML in parthenogenesis and a newly discovered role for a member of the BBM-like clade of APETALA 2 transcription factors.…”

“…In gametophytic apomixis, a chromosomally unreduced embryo sac develops from the megaspore mother cell (diplospory) or from a nearby nucellar cell (apospory) in a process termed apomeiosis. Parthenogenesis, the development of the unreduced, unfertilized egg into an embryo, constitutes the second step of the apomictic process (1,2).…”

The cutting effect of male flower on the size of the fruit cob, the size of the fruit and seeds in Porang (Amorphophallus muelleri Blume)

“…22 Initial cells that later develop into apomixis seeds are nucleus cells, integument cells, epidermal cells of the lining of LI and LII of ovule. 23 In this study, the presence of apomixis seeds in more than one in one individual fruit can be known from the measurement of the individual diameter of the fruit. The individual diameter of the fruit of the cut-male flower tends to be wider than the normal flower.…”

Flower Development and Its Implication for Seed Production on Amorphophallus muelleri Blume (Araceae)

“…However, many farmers remove flower buds in order to maintain high glucomannan production, thus flowering of A. muelleri plants are rare in fields (Santosa et al, 2003). Flowers produce triploid (2n=3x=39) apomictic seeds (Jansen et al, 1996); thus progenies are genetically identical to the maternal plant (Hand and Koltunow, 2014), preventing cross breeding. Therefore, there were few studies on flower morphology and flowering phenology.…”