Expression of maize eukaryotic initiation factor (eIF) iso4E is regulated at the translational level

Area of Science:

• Molecular Biology
• Plant Science
• Gene Expression Regulation

Background:

• Translational control is crucial for eukaryotic gene expression during development.
• Insulin/growth factors regulate eukaryotic initiation factor (eIF) 4E availability, a key translational control point.

Purpose of the Study:

• To investigate the regulatory mechanisms of differential expression between eIF4E and eIFiso4E in maize embryonic axes during germination.
• To elucidate the role of insulin signaling in regulating these translation factors.

Main Methods:

• Comparing de novo synthesis rates of eIF4E and eIFiso4E in maize axes.
• Assessing the impact of insulin addition on protein synthesis and mRNA recruitment.
• Utilizing signal-transduction pathway inhibitors (wortmannin, rapamycin).
• Conducting in vitro translation assays with phosphorylated and non-phosphorylated ribosomes.

Main Results:

• eIFiso4E synthesis initiates earlier and is faster than eIF4E in maize axes.
• Insulin stimulated eIFiso4E synthesis and its transcript recruitment into polysomes, an effect reversed by pathway inhibitors.
• Phosphorylated ribosomes enhanced eIFiso4E translation in vitro, but not eIF4E translation.

Conclusions:

• Maize embryonic axes regulate eIFiso4E, not eIF4E, cell content via de novo synthesis during germination.
• Regulation likely involves specific mRNA polysome recruitment through an insulin-dependent signal-transduction pathway involving S6 ribosomal protein phosphorylation.