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. Author manuscript; available in PMC: 2022 Jul 6.
Published in final edited form as: Wiley Interdiscip Rev RNA. 2020 May 4;11(6):e1597. doi: 10.1002/wrna.1597

Figure 2: Regulation of translatomes in pollen development and seed germination.

Figure 2:

Yellow boxes indicate translation state, abundance of polysome or monosomes and cellular RNP complexes; blue (pink) boxes indicate functional gene ontology terms that are translationally active (repressed); green boxes indicate examples of translationally repressed mRNAs corresponding to a specific developmental stage.

(A) Pollen. The vertical timeline covers (pre-)meiotic (sporophytic, diploid) followed by postmeiotic (gametophytic, haploid) stages of tobacco pollen. Early stage proteomes are characterized by abundant heat shock protein chaperones (HSPs), RNA binding proteins (RBPs), cell wall loosening enzymes and protein degradation, while the later gametophytic stage is rich in glycolytic and fermentation enzymes and late embryo abundant (LEA) proteins. LEA proteins are linked to ABA signaling, cell wall synthesis and the maintenance of ROS balance. Mature, desiccated pollen grains contain a high amount of monosomes in the form of special structures called EDTA/Puromycin resistant Particles (EPPs), which are translationally inactive. EPPs contain stalled monosomes on transcripts maintained in a translationally quiescent state, to be released for translation towards the maturation phase of pollen germination. The EPP proteome contains ribosomal 60S proteins and translation initiation and elongation factors. Examples of the mature pollen EPP transcriptome include pollen-specific cell wall glycoprotein (NTP303 ortholog ATSKU5) and pollen-specific LIM domain containing protein (WLIM2B). After Hafidh et al., 2018 and Ischebeck et al., 2014. (B) Seed germination begins with a dry seed (top=early) and involves two distinct translational shifts, coincident with seed hydration and root protrusion (‘germination’ proper). During the hydration shift (0–6 h after imbibition) transcripts found abundant in the last stages of seed maturation become polysome loaded and actively translated (e.g. PM1 is translated during this phase and suppresses the translation of a glycine-rich protein). The second translational shift (26–48 h) occurs between testa rupture and root protrusion. At this stage, abundant polysomes contain transcripts related to RNA processing and modification and lipid metabolism. After Bai et al., 2017, Bai et al., 2020.