Expression Profile of Maize (Zea mays L.) Embryonic Axes During Germination: Translational Regulation of Ribosomal Protein mRNAs

Abstract

Seed germination is a critical developmental period for plant propagation. Information regarding gene expression within this important period is relevant for understanding the main biochemical processes required for successful germination, particularly in maize, one of the most important cereals in the world. The present research focuses on the global microarray analysis of differential gene expression between quiescent and germinated maize embryo stages. This analysis revealed that a large number of mRNAs stored in the quiescent embryonic axes (QEAs) were differentially regulated during germination in the 24 h germinated embryonic axes (GEAs). These genes belong to 14 different functional categories and most of them correspond to metabolic processes, followed by transport, transcription and translation. Interestingly, the expression of mRNAs encoding ribosomal proteins [(r)-proteins], required for new ribosome formation during this fast-growing period, remains mostly unchanged throughout the germination process, suggesting that these genes are not regulated at the transcriptional level during this developmental period. To investigate this issue further, comparative microarray analyses on polysomal mRNAs from growth-stimulated and non-stimulated GEAs were performed. The results revealed that (r)-protein mRNAs accumulate to high levels in polysomes of the growth-stimulated tissues, indicating a translational control mechanism to account for the rapid (r)-protein synthesis observed within this period. Bioinformatic analysis of (r)-protein mRNAs showed that 5' TOP (tract of pyrimidines)-like sequences are present only in the 5'-untranslated region set of up-regulated (r)-protein mRNAs. This overall approach to the germination process allows an in-depth view of molecular changes, enabling a broader understanding of the regulatory mechanisms that occur during this process.

The Arabidopsis TOR Kinase Specifically Regulates the Expression of Nuclear Genes Coding for Plastidic Ribosomal Proteins and the Phosphorylation of the Cytosolic Ribosomal Protein S6

“…This motif is reminiscent of TOP motifs ( Figure 4A ). A TOP-like motif was also previously identified in mRNA coding for ribosomal proteins in maize embryonic axes (Jiménez-López et al, 2011) but these motifs are so far poorly described in plants. Canonical TOP motifs are located at the start of the mRNA, which is not the case in our analysis.…”

Dynamic Light Regulation of Translation Status in Arabidopsis thaliana

“…By contrast, these mRNAs are translationally activated in maize embryos during germination (Jimenez-Lopez et al, 2011). Our further demonstration of coordinate repression of translation of these transcripts in a meta-analysis comparing modulation of light and oxygen availability (Figure 9), complements an earlier comparison of change in translation status in response to elevated temperature, salt stress, and dehydration stress (Matsuura et al, 2010).…”

The 5′ untranslated region of the soybean cytosolic glutamine synthetase β1 gene contains prokaryotic translation initiation signals and acts as a translational enhancer in plants

“…It has also been found that the 40S ribosomal protein binds to the 5′UTR of the turnip crinkle virus RNA at a 19 nucleotide pyrimidine-rich element that enhances translational activity (Stupina et al 2011). Phosphorylation of RPS6 by S6 kinases following stimulation by auxin and insulin treatments in maize leads to the translational activation of TOP-mRNAs encoding proteins associated with cell proliferation and growth (Beltrán-Peña et al 2002; Jiménez-López et al 2011). The presence of the oligopyrimidine track in the 5′UTR of the Gm glnβ 1 RNA suggests that its translation may be subjected to a TOP-like translational control.…”