Phytochrome Control of Specific mRNA Levels in Developing Pea Buds

Abstract

We have examined phytochrome regulated changes in transcript abundance for 11 different light regulated mRNAs in developing pea buds. Fluence-response curves were measured for changes in transcript abundance in response to red light pulses in both the low and very low fluence ranges. Most bean (25). In Lemna it has been shown that phytochrome affects transcription of the cab and rbcS genes in isolated nuclei (23).Phytochrome regulation occurs over two fluence ranges of R (5, 7, 20). The LF response has a threshold of approximately 10' ,umol m-2 and is fully reversible by FR. This is the common phytochrome response observed in most plants. The VLF response has a threshold ofapproximately 10-3 gmol m-2. It is not reversible by FR; indeed it is induced by most FR sources (5,7,20).To date, the VLF response has only been observed in a limited number ofsystems. These include growth rates ofetiolated Avena coleoptiles and mesocotyls (3,20), anthocyanin synthesis in mustard seedlings (4), and germination of dormant lettuce seeds (6,7,24). A VLF response for Chl accumulation in peas is apparent if R of varying fluence is used as a pretreatment followed by a dark period and a subsequent white light treatment (18,22). Recently, we have also demonstrated, using etiolated pea buds, that cab transcripts have both a VLF and a LF response, whereas rbcS transcripts exhibit only a LF response (17).The mechanism whereby phytochrome regulates transcription and/or transcript abundance is unknown. In this paper, we describe the basic characteristics of phytochrome control for 11 unidentified phytochrome regulated messages and further characterize the phytochrome responses of cab and rbcS transcripts. We have measured the fluence-dependent accumulation of these transcripts in response to single pulses of R, the ability of FR to reverse these R effects, and the ability of FR to induce transcript accumulation in the absence of prior R treatments.We have also used a pretreatment protocol similar to that described above which demonstrates an effect of VLF R for Chl accumulation in a subsequent white light period (18,22

Light Quality and Irradiance Level Interaction in the Control of Expression of Light-Harvesting Complex of Photosystem II

“…This switching is initiated at very low irradiance levels, and genes coding for light-harvesting complexes and ribulose bisphosphate carboxylase apparently have different levels of very low fluence activation (17). However, the action of phytochrome during early development may be different from that found during long-term growth because most reactions escape from phytochrome reversibility after 24 to 48 h of continuous irradiation (15,24).…”

Both internal and external regulatory elements control expression of the pea Fed-1 gene in transgenic tobacco seedlings.

“…Fed-7, a singlecopy nuclear gene encoding ferredoxin I (Dobres et al, 1987;Elliott et al, 1989b), exhibits a number of unusual light responses in the buds of etiolated pea seedlings (Kaufman et al, 1985(Kaufman et al, , 1986. We have argued that these differences indicate that Fed-7 regulatory mechanisms probably differ from those of other light-responsive genes (Thompson, 1988).…”

Circadian Control of the Accumulation of mRNAs for Light- and Heat-Inducible Chloroplast Proteins in Pea (Pisum sativum L.)

“…the mRNA for LHCP3 is expressed 1 or 2 d before that for ssRuBPCase (35). Finally, the extent of mRNA accumulation depends on light intensity (10,13). 'The authors are grateful for the generous financial support by the Deutsche Forschungsgemeinschaft, Bonn, FRG.…”