Transcriptional and post-transcriptional regulation of gene expression in developing barley endosperm

Abstract

The expression of the genes encoding B-, C-, D- and γ-hordein, protein Z, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and histone H3 has been studied in developing barley endosperms. The levels of the mRNAs encoding hordein and protein Z increase 3- to 4-fold from 8 to 25 days after anthesis and thereafter decrease, whereas the GAPDH and histone H3 mRNAs are constant from 8 to 15 days and then decline. B- and C-hordein mRNAs are 7 to 100 times more abundant than any of the other mRNA species. Analysis of the transcription rate of the genes encoding B-, C- and D-hordein and protein Z in isolated endosperm nuclei revealed that the rate is correlated with their copy number in the genome. A comparison of the steady-state levels of endosperm-specific mRNA species with the in vitro transcription rates of their respective gene families suggests that the high levels of B- and C-hordein mRNAs are the result of post-transcriptional regulation. Mutant hor 2ca, defective in B-hordein synthesis, has a substantial increase in the level of mRNAs coding for C-hordein and GAPDH, whereas the levels of the other mRNAs are unaffected. In mutant lys 3a, which fails to synthesize the major storage polypeptides, the mRNA levels of B-, C- and γ-hordein and protein Z are dramatically reduced. The in vitro transcription activity of the genes encoding B- and C-hordein and protein Z is 50-fold lower in lys 3a nuclei than in the wild type, accounting for the reduced level of mRNAs and storage protein synthesis in this mutant. © 1989 Springer-Verlag.