Exploring the sister cells of embryo sac: developmental and functional attributes

Abstract

Synergids are metabolically dynamic cells of the egg apparatus and represent an important component of the female gametophyte. Besides directing the growth of the pollen tube towards the micropylar end of the embryo sac, these ephemeral structures make room for the pollen tube cytoplasm. Nature of chemotrophic substances that direct the growth of the pollen tube, the mechanism of degeneration of one of the synergids before fertilization and the molecular aspects of synergid morphogenesis have been studied in detail. Research carried out on model systems such as Arabidopsis, Brassica, Capsella, Triticum and Torenia has bettered our understanding of the molecular regulation of the pollen tube journey, its guidance and navigation in the pistil. Recently, the critical role of the central cell in fertilization and prevention of polytuby has also been thoroughly investigated. Interesting aspects that lead to degeneration of synergids, and the factors governing degeneration including molecular aspects have brought a paradigm shift in understanding of these intriguing units. Sophisticated confocal microscopy, live cell imaging, and molecular tools have helped in furthering our knowledge in the functioning of synergids. Recent research using the high throughput techniques have deciphered the role of various genes that regulate and govern the release of chemotropic substances, cell to cell interaction and synergid cell degeneration. Also, with the diversity displayed in form and function of organs in the angiosperms, and the switching over of roles of the cells of egg apparatus many new insights have been provided on the involvement of synergids both pre- and post-fertilization. Present review provides a comprehensive account of synergids, their role in fertilization and the post fertilization events that have emerged using interdisciplinary approaches in recent years. We also discuss the variations observed in degeneration of synergids and the mechanisms that have been unravelled lately. Looking at the dynamism synergids display, newer roles of these are emerging in fertilization. It is still unknown how synergids in angiosperm taxa where genetic transformation/alteration is carried out, will respond to pollen stimuli. Considering the environmental factors also a role to play in synergid functions, there is lack of experimental studies in this direction. Further research in developing adequate protocols for manipulating synergid functions is much desired. This research has enormous potential in advancement of basic science and can find applications in agriculture, horticulture, and bioprospecting.

Understanding megasporogenesis through model plants: contemporary evidence and future insights

“…there are many independent aspects which come into action during megasporogenesis, such as regulation of the cell cycle, hormonal interplay, ribosome biogenesis, protein degradation and epigenetic pathways (Simpson, 2019). all these pathways are interconnected and operate via cell-to-cell communication in the developing ovule and its components (Kaur and Koul, 2022). Cell fate transition (somatic cell to germline cell transition) is accompanied by a large-scale chromatin reprogramming which is partially synchronous with meiotic S phase.…”