Transcriptional and post-transcriptional regulation of ribulose 1,5-bisphosphate carboxylase gene expression in light- and dark-grown amaranth cotyledons.

Abstract

The regulation of expression of the genes encoding the large subunit (LSU) and small subunit (SSU) of ribulose 1,5-bisphosphate carboxylase (RuBPCase) was examined in 1-through 8-day-old, dark-grown (etiolated) and light-grown amaranth cotyledons. RuBPCase specific activity in light-grown cotyledons increased during this 8-day period to a level 15-fold higher than in dark-grown cotyledons. Under both growth conditions, the accumulation of the LSU and SSU polypeptides was not coordinated. Initial detection of the SSU occurred 1 and 2 days after the appearance of the LSU in light-and dark-grown cotyledons, respectively. Furthermore, although the levels of the LSU were similar in both light-and dark-grown seedlings, the amount of the SSU followed clearly the changes in enzyme activity. Synthesis of these two polypeptides was dramatically different in etiolated versus light-grown cotyledons. In light the synthesis of both subunits was first observed on day 2 and continued throughout the growth of the cotyledons. In darkness the rate of synthesis of both subunits was much lower than in light and occurred only as a burst between days 2 and 5 after planting. However, mRNAs for both subunits were present in etiolated cotyledons at similar levels on days 4 through 7 (by Northern analysis) and were functional in vitro, despite their apparent inactivity in vivo after day 5. In addition, since both LSU and SSU mRNA levels were lower in dark-than in light-grown seedlings, our results indicate that both transcriptional and post-transcriptional controls modulate RuBPCase production in developing amaranth cotyledons.Ribulose 1,5-bisphosphate carboxylase (RuBPCase) is located in the chloroplasts of all higher plants and is the primary enzyme of photosynthetic carbon fixation. This enzyme has a molecular weight of about 550,000 and consists of eight large (51-to 58-kilodalton [kDa]) and eight small (12-to 18-kDa) subunits (46

Inducible Expression, Enzymatic Activity, and Origin of Higher Plant Homologues of Bacterial RelA/SpoT Stress Proteins in Nicotiana tabacum

“…RNA Extraction and Northern blot Analysis-Isolation of total RNA from leaves of tobacco and other plants and Northern analysis were performed according to methods previously described (5)(6)(7)(8). For the Nt-RSH2 probe used in Fig.…”

mRNAs encoding ribulose-1,5-bisphosphate carboxylase remain bound to polysomes but are not translated in amaranth seedlings transferred to darkness

“…hypochondriacus var. R103 was grown as described (13). For light-to-dark transitions, plants grown under normal illumination for 6 days were transferred to lightproof boxes in a darkroom for various times before harvesting.…”

“…7 green safelight. Analyses of in vivo protein synthesis and mRNA accumulation were as described (13).…”

“…In several cases alterations in transcriptional activity have been shown to be responsible for these changes in mRNA levels (9). At the other end of the spectrum, regulation at the posttranslational level via turnover of the protein (10) as well as by activation (1, 11) or inhibition (12) of the enzyme's activity has also been reported.We have previously described the effects of environmental (light) (13,14) or developmental (13, 15) signals on the expression of LS and SS genes in the C4 dicotyledonous plant Amaranthus hypochondriacus. The expression of these genes is regulated not only at the level of mRNA accumulation but also posttranscriptionally.…”

“…We have previously described the effects of environmental (light) (13,14) or developmental (13, 15) signals on the expression of LS and SS genes in the C4 dicotyledonous plant Amaranthus hypochondriacus. The expression of these genes is regulated not only at the level of mRNA accumulation but also posttranscriptionally.…”