Translation of Ribosomal Protein mRNAs in Maize Axes

Abstract

The objective of this research is to study the mechanism(s) regulating ribosomal protein (rp) mRNA translation during maize germination. Northern analysis of RNA from non-germinated maize embryonic axes revealed rp-transcripts within the stored mRNA pool. S₄ and S₆ rp transcripts were stored as mature mRNAs while others seemed to be as pre-mRNAs. Preferential translation of rp-mRNAs was observed early in germination, as indicated by in vivo pulse labelling experiments with ³⁵S-methionine. Mobilization of S₆-transcript from ribonucleoprotein particles to polysomes was followed during germination. The effects of different hormones and environmental stresses were tested on this process. Recruitment of S₆ rp-transcript was found to be affected by insulin and stress. Inhibitors of either protein-phosphatases or kinases altered this process suggesting that it could be regulated by phosphorylation/dephosphorylation of protein(s) related to the translational apparatus. Insulin caused an increase in phosphorylation of the ribosome integrated S₆ protein. These data suggest that S₆ phosphorylation might be involved in the mechanism responsible for rp-mRNA recruitment into polysomes. Consequently, in maize axes translation of rp-mRNA might be regulated by a signal transduction mechanism similar to other eukaryotic cells.