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

Abstract

AbstractEndosperm 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 inPanicum. 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.