Tissue-specific expression of phosphoenolpyruvate carboxylase in sorghum

Abstract

The synthesis and expression of phosphoenolpyruvate carboxylase (PEP-C) mRNA in sorghum tissue (i.e., leaf, shoot, and root) were monitored for several days after seed germination by Northern hybridization and measurement of de novo protein synthesis. In 2- to 8-day-old leaves and shoots, PEP-C accounted for approximately 8.9 and 2.5%, respectively, of the newly synthesized proteins. In addition, mRNA from both leaves and shoots, detected by hybridization with a heterologous PEP-C probe, is present in relatively constant amounts from 2 to 9 days after seed germination. In roots, on the contrary, a peak of RNA that hybridizes to the probe was observed approximately 6 days after seed germination, when de novo synthesis of the enzyme was barely detectable in this tissue. Northern hybridization experiments indicate the presence of putative mRNA species of approximately 3.1 and 5.9 kilobases. The data are rationalized in terms of the postulated existence of a stable but translationally inactive precursor of PEP-C mRNA in sorghum roots.