Endosperm variability: from endoreduplication within a seed to higher ploidy across species, and its competence

Abstract

Endosperm tissue that nourishes the embryo during seed development, upon maturity, nourishes the global population with special reference to cereal crops like maize, wheat and rice. In about 70% of the angiosperms, endosperm genome content is ‘3n’ with 2:1 (maternal:paternal) contribution, as a result of the second fertilization event. However, angiosperms evolution also documents diversity in endosperm genome content from ‘2n’ to ‘15n’, in scale with the corresponding maternal genome dosage variability (‘1n’ to ‘14n’), whereas paternal contribution is invariable. In apomicts, due to lack of fertilization, or pseudogamy (fertilization of the central cell for endosperm formation), endosperm genome dosage (m:p) has been reported to range between 1:1 and 8:3. Exceptionally, the central cell with one unreduced nucleus and fused with a reduced sperm cell, with 2:1 normal genome dosage, has been reported in Panicum. Altered genome dosage levels are reportedly correlative with eccentricities among maternal and paternal contribution to seed resource allocation. Besides endosperm ploidy variability between species of angiosperms, the present review gives an overview of the ploidy variability in endosperm cells within a seed, up to ‘690n’. In addition to genome-scale variability in the endosperm, some taxa of angiosperms exhibit chlorophyllous endosperms and some chlorophyllous embryos. Also, endosperm cell number during seed development is reported to have a strong association with grain weight at maturity. Genes underlying these traits of variability are unknown, and the present review underscores the variability and highlights the potential of the single-cell sequencing techniques towards understanding the genetic mechanisms associated with these variable traits.

Can omic tools help generate alternative newer sources of edible seed oil?

“…Understanding the gene regulatory networks in plants that produce oil in the endosperm (Reynolds et al, 2019 ) might help define strategies to synthesize oil in the endosperm of the cereal crops and other crops where the endosperm is chlorophyllous in nature (Rangan, 2020 , and citations thereof). Utilizing the strengths of endosperm‐specific callus cell cultures could be a commercially viable option in the near future with successful demonstration of developing cell cultures producing TAG (Carmona‐Rojas et al, 2021 ).…”

Comparative transcriptomics of seed nourishing tissues: uncovering conserved and divergent pathways in seed plants

“…In fact, seed nourishing tissues have substantially diverged in morphology and developmental patterns throughout the more than 300 million years since angiosperms diverged from their common gymnosperm ancestor (Lubna et al., 2021; Ran et al., 2018; Zimmer et al., 2007). For instance, endosperms of different species can have varying ploidies and maternal to paternal genome ratios, depending on the type of megagametogenesis that occurs in each given species, and on the type of reproduction, sexual or asexual (Baroux et al., 2002; Geeta, 2003; Rangan, 2020). Moreover, endosperms can follow different modes of development (Floyd & Friedman, 2000): nuclear endosperms, like those of Arabidopsis thaliana and of cereals, are coenocytic in the first stages of development, and only cellularize at a later time point (Olsen, 2004); while in cellular endosperms, like those of the Solanaceae, Lamiales and of early diverging angiosperms, karyokinesis is always coupled to cytokinesis (Oneal et al., 2016; Povilus et al., 2015; Roth et al., 2018); finally, in the more uncommon helobial endosperms, two chambers are formed, each of which undergoes a different developmental program (Swamy & Parameswaran, 1963).…”

Comparative transcriptomics of seed nourishing tissues: uncovering conserved and divergent pathways in seed plants

“…In fact, seed nourishing tissues have substantially diverged in morphology and developmental patterns throughout the more than 300 million years since angiosperms diverged from their common gymnosperm ancestor (Zimmer et al ., 2007; Ran et al ., 2018; Lubna et al ., 2021). For instance, endosperms of different species can have varying ploidies and maternal to paternal genome ratios, depending on the type of megagametogenesis that occurs in each given species, and on the type of reproduction, sexual or asexual (Baroux et al ., 2002; Geeta, 2003; Rangan, 2020). Moreover, endosperms can follow different modes of development (Floyd & Friedman, 2000): nuclear endosperms, like those of Arabidopsis thaliana and of cereals, are coenocytic in the first days of development, and only cellularize at a later time point (Olsen, 2004); while in cellular endosperms, like those of the Solanaceae, Lamiales and of early diverging angiosperms, karyokinesis is always coupled to cytokinesis (Povilus et al ., 2015; Oneal et al ., 2016; Roth et al ., 2018); finally, in the more uncommon helobial endosperms, two chambers are formed, each of which undergoes a different developmental program (Swamy & Parameswaran, 1963).…”