Transcriptional activity of Hyacinthus orientalis L. female gametophyte cells before and after fertilization

Abstract

We characterized three phases of Hyacinthus orientalis L. embryo sac development, in which the transcriptional activity of the cells differed using immunolocalization of incorporated 5′-bromouracil, the total RNA polymerase II pool and the hypo- (initiation) and hyperphosphorylated (elongation) forms of RNA Pol II. The first stage, which lasts from the multinuclear stage to cellularization, is a period of high transcriptional activity, probably related to the maturation of female gametophyte cells. The second stage, encompassing the period of embryo sac maturity and the progamic phase, involves the transcriptional silencing of cells that will soon undergo fusion with male gametes. During this period in the hyacinth egg cell, there are almost no newly formed transcripts, and only a small pool of RNA Pol II is present in the nucleus. The transcriptional activity of the central cell is only slightly higher than that observed in the egg cell. The post-fertilization stage is related to the transcriptional activation of the zygote and the primary endosperm cell. The rapid increase in the pool of newly formed transcripts in these cells is accompanied by an increase in the pool of RNA Pol II, and the pattern of enzyme distribution in the zygote nucleus is similar to that observed in the somatic cells of the ovule. Our data, together with the earlier results of Pięciński et al. (2008), indicate post-fertilization synthesis and the maturation of numerous mRNA transcripts, suggesting that fertilization in H. orientalis induces the activation of the zygote and endosperm genomes.

Late progamic phase and fertilization affect calreticulin expression in the Hyacinthus orientalis female gametophyte

“…The results of our study indicate that prior to anthesis, all cells from the Hyacinthus embryo sac exhibit an accumulation of CRT mRNA, but significant differences in distribution pattern of investigated transcripts appear after flower opening, followed by the fusion of gametes. The observed changes in the expression of CRT in the cells that were involved in double fertilization are correlated in time with result previously reported by our group regarding the total transcriptional activity of Hyacinthus female gametophyte, whose level is comparable prior to anthesis but changes in response to flower opening, gamete fusion and early embryogenesis (Niedojadło et al 2012a ).…”

“…During the period preceding fertilization, from anthesis to the late progamic phase, the highest transcriptional activity of CRT was observed in synergids and in the central cell, while the metabolically silent egg cell exhibited reduced level of CRT expression (Niedojadło et al 2012a and this work). Furthermore, during the progamic phase, there were clear differences in CRT expression in both synergids, in which mRNA CRT distribution is analogous to the location of incorporated 5′-bromouracil (BrU); the particular accumulation of these molecules occurs in the cytoplasm of sister synergids below the FA (Niedojadło et al 2012a and this work).…”

“…During the period preceding fertilization, from anthesis to the late progamic phase, the highest transcriptional activity of CRT was observed in synergids and in the central cell, while the metabolically silent egg cell exhibited reduced level of CRT expression (Niedojadło et al 2012a and this work). Furthermore, during the progamic phase, there were clear differences in CRT expression in both synergids, in which mRNA CRT distribution is analogous to the location of incorporated 5′-bromouracil (BrU); the particular accumulation of these molecules occurs in the cytoplasm of sister synergids below the FA (Niedojadło et al 2012a and this work). These observations are consistent with previous results that were obtained for dicotyledonous Petunia (Lenartowski et al 2014 ) and indicate that the progamic phase is a period of increased transcriptional activity of CRT in cells whose participation in the adoption of the growing pollen tube is crucial (Kessler and Grossniklaus 2011 ; Bleckmann et al 2014 ).…”

“…Commercial cultivars of Hyacinthus orientalis L. were grown at room temperature. The Hyacinthus pistil is composed of a hollow style and a dry stigma, while the female gametophyte develops according to the Polygonum type and consists of two synergids, the egg cell, the central cell containing two polar nuclei, and three antipodals (Pięciński et al 2008 ; Niedojadło et al 2012a , b , 2015 ). For fluorescence and electron microscopy studies, the ovules were mechanically dissected from unpollinated flowers before and during anthesis and from hand-cross-pollinated flowers 8 h after pollination (at the late progamic phase when the pollen tubes have reached approximately three-quarters of the style length and have not entered the ovary) and 96 h after pollination (fertilized ovules).…”

Transcriptional Activation of Arabidopsis Zygotes Is Required for Their Initial Division

“…Histological and molecular evidence in Hyacinthus orientalis (hyacinth, (Niedojadło et al, 2012;Pięciński et al, 2008), Nicotiana tabacum (tobacco, (Ning et al, 2006;Zhao et al, 2011), Oryza sativa (rice, (Abiko et al, 2013;Anderson et al, 2013;Anderson et al, 2017;Ohnishi et al, 2014;Ohnishi et al, 2019), Triticum aestivum (wheat, (Domoki et al, 2013;Sprunck et al, 2005) and Zea mays (maize, (Chen et al, 2017;Dresselhaus et al, 1999;Meyer and Scholten, 2007;Okamoto et al, 2005;Sauter et al, 1998) altogether indicate that large-scale transcriptional activities increase in zygotes after fertilization and prior to the first division. These results suggest that, similar to animals, plant zygotic genomes may also transition from a transcriptionally quiescent to active state.…”