Translation efficiency of Lea mRNAs in cotton embryos: minor changes during embryogenesis and germination.

In earlier studies, only two major patterns of transcript accumulation were seen for 18 late embryogenesis abundant (Lea) gene families in cotton (Gossypium hirsutum L.) during embryogenesis and early germination. Each of these gene families probably comprises two active alloalleles. The two polypeptides encoded by seven of the Lea families can be distinguished, and analysis of their translation in vitro indicated that regulation of the homeologous transcript abundance was similar in each.In the present study, two-dimensional gel electrophoresis of polypeptides synthesized in excised embryos was employed to determine if LEA polypeptide synthesis is regulated at the translational level. The relative in vivo synthesis rate of each of the two polypeptides of 7 Lea families was compared with the relative concentration of their transcripts measured earlier by in vitro translation. For 4 families, the relative translational efficiencies of the homeologous mRNAs do not change during embryogenesis. However, there are changes of 1.5-3-fold in the other 3 families. The translation efficiencies of all transcripts of 9 of the Lea family mRNAs in vivo can be calculated from the fraction of total protein radioactivity incorporated in each LEA polypeptide family and the fractional abundance of Lea family transcripts measured by RNA dot hybridization. Lea mRNAs are found to be translated at near average rates throughout embryogenesis and early germination. These observations suggest that regulation of Lea gene expression at the translational level is minor.