Abstract
Eukaryotic translation initiation factor 3 (eIF3) is a large protein complex that participates in most translation initiation processes. While eIF3 has been well characterized, less is known about the roles of individual eIF3 subunits, particularly in plants. Here, we identified and characterized OseIF3e in rice (Oryza sativa L.). OseIF3e was constitutively expressed in various tissues, but most strongly in vigorously growing organs. Transgenic OseIF3e-silenced rice plants showed inhibited growth in seedling and vegetative stages. Repression of OseIF3e led to defects in pollen maturation but did not affect pollen mitosis. In rice, eIF3e interacted with eIF3 subunits b, d, e, f, h, and k, and with eIF6, forming homo- and heterodimers to initiate translation. Furthermore, OseIF3e was shown by yeast two-hybrid assay to specifically bind to inhibitors of cyclin-dependent kinases 1, 5, and 6. This interaction was mediated by the sequence of amino acid residues at positions 118–138, which included a conserved motif (IGPEQIETLYQFAKF). These results suggested although OseIF3e is not a “functional core” subunit of eIF3, it still plays crucial roles in rice growth and development, in combination with other factors. We proposed a pathway by which OseIF3e influence organ size and pollen maturation in rice, providing an opportunity to optimize plant architecture for crop breeding.
Highlights
In the process of translation initiation, eukaryotic initiation factors participate in the recruitment of initiator tRNA (Met-tRNAiMet) and mRNA to the 40S ribosomal subunit, as well in scanning for the AUG start codon (Browning et al, 2001; Kapp and Lorsch, 2004; Hinnebusch, 2006)
OseIF3e was originally identified via its interaction with the basal transcription factor Osj10gBTF3, inhibition of which results in plant miniaturization and pollen abortion (Wang et al, 2012)
To investigate the expression profile of OseIF3e, we searched the CREP (Collection of Rice Expression Profiles) database8, which collects genome-wide expression data over the life cycles of two rice varieties (Wang et al, 2010). This revealed OseIF3e to be constitutively expressed in all tissues and organs, with high expression levels in young and developing tissues (Supplementary Table S1 and Figure S1)
Summary
In the process of translation initiation, eukaryotic initiation factors (eIFs) participate in the recruitment of initiator tRNA (Met-tRNAiMet) and mRNA to the 40S ribosomal subunit, as well in scanning for the AUG start codon (Browning et al, 2001; Kapp and Lorsch, 2004; Hinnebusch, 2006). Of the 12 known eIFs, eukaryotic translation initiation factor 3 (eIF3) is the largest and most complex It is involved in assembling the eIF2-GTP-Met-tRNAiMet ternary complex and recruiting it to the 40S subunit, recruiting mRNA to the 43S pre-initiation complex, and scanning for and recognizing AUG start codons (Burks et al, 2001; Kawaguchi and Bailey-Serres, 2002; Siridechadilok et al, 2005; Hinnebusch, 2006). The non-conserved nature of subunit e indicates that it may not be essential for translation initiation (Asano et al, 1998; Burks et al, 2001; Zhou et al, 2005; Xia et al, 2010)
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