Regulation of mRNA translation controls seed germination and is critical for seedling vigor

Citation: Galland M and Rajjou L (2015) Regulation of mRNA translation controls seed germination and is critical for seedling vigor. The control of seed germination capacity is a multi-level molecular process including, epigenetic, transcriptional, post-transcriptional, translational, and post-translational regulation (Rajjou et al., 2012). Since the beginning of the twenty-first century, a wide range of genetic, genomic, and post-genomic approaches have been used to decipher the underlying molecular and biochemical bases of dormancy, vigor, and longevity. In particular, the regulation of stored mRNA translation appears as an essential determinant of seed quality. Indeed, proteomic approaches unveiled the main importance of protein synthesis during seed germination (Rajjou et al., 2004; Kimura and Nambara, 2010), as well as factors involved in seed longevity (Rajjou et al., 2008). In aged seeds, the protein synthesis capacity decline together with the loss of germination potential. In contrast, both dormant and non-dormant Arabidopsis seeds display equal translational activity 1 day after imbibition although distinct protein pools are synthetized (Chibani et al., 2006). In sunflower, seed dormancy release by after-ripening would not be related to transcriptomic changes but associated with oxidation of specific subsets of stored mRNAs, thus impairing their translation (Bazin et al., 2011; Meimoun et al., 2014). In the aim to get a comprehensive view of translational control of seed dormancy and germination in sunflower, a microarray-based translatome analysis was performed, highlighting differential accumulation of polysome-associated mRNAs between dormant and non-dormant imbibed seeds (Layat et al., 2014). However, multiple ribosomes are not necessarily translationally active. Indeed, it has been observed that both active and stalled ribosomes are able to co-sediment during isolation of polysome complexes (Sivan et al., 2007). As a result, polysome profiling does not fully discriminate translationally active from repressed mRNAs. This concern should be particularly true in the case of dry seeds where polysomes would not be functional. Indeed, it has been observed that the ribosomes are condensed into regions consisting of closely packed particles in the dry seed related with a latent potential for protein synthesis (Chapman and Rieber, 1967). A rapid polysome formation occurs during early germination related with the transition from a dry and quiescent state to a fully imbibed and metabolically active state. In non-dormant Arabidopsis seeds, the comparison between the transcript changes and the protein changes from dry to 1d-imbibed seeds showed strong discordance (Galland et al., 2012). This is in accordance with previous work in plants reporting …