Light-mediated control of translational initiation of ribulose-1, 5-bisphosphate carboxylase in amaranth cotyledons.
In cotyledons of 6-day-old amaranth seedlings, the large subunit (LSU) and the small subunit (SSU) polypeptides of ribulose-1,5-bisphosphate carboxylase are not synthesized in the absence of light. When dark-grown seedlings were transferred into light, synthesis of both polypeptides was induced within the first 3 to 5 hr of illumination without any significant changes in levels of their mRNAs. In cotyledons of light-grown seedlings and of dark-grown seedlings transferred into light for 5 hr (where ribulose-1,5-bisphosphate carboxylase synthesis was readily detected in vivo), the LSU and SSU mRNAs were associated with polysomes. In cotyledons of dark-grown seedlings, these two mRNAs were not found on polysomes. In contrast to the SSU message, mRNAs encoding the nonlight-regulated, nuclear-encoded proteins actin and ubiquitin were associated with polysomes regardless of the light conditions. Similarly, mRNA from at least one chloroplast-encoded gene (rpl2) was found on polysomes in the dark as well as in the light. These results indicate an absence of translational initiation in cotyledons of dark-grown seedlings which is specific to a subset of nuclear- and chloroplast-encoded genes including the SSU and LSU, respectively. Upon illumination, synthesis of both polypeptides, and possibly other proteins involved in light-mediated chloroplast development, was induced at the level of translational initiation.
Berry
J O
JO
Waksman Institute, Rutgers, State University of New Jersey, Piscataway 08855.
Breiding
D E
DE
Klessig
D F
DF
D002736:Chloroplasts / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D008027:Light; D010442:Peptide Chain Initiation, Translational / Q000528:radiation effects*; D010940:Plant Proteins / Q000235:genetics; D010944:Plants / Q000235:genetics*; D011132:Polyribosomes / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics*
D010940:Plant Proteins; D012333:RNA, Messenger; D012273:Ribulose-Bisphosphate Carboxylase