Phytochrome Control of Specific mRNA levels in Developing Pea Buds

Abstract

ABSTRACIWe have examined the time course for accumulation of each of 12 different nuclear gene transcripts in pea buds after irradiating dark grown seedlings with a single pulse low fluence red light (103 micromoles per square meter delivered in 100 seconds). The 12 time courses can be grouped into four general classes. Six transcripts (including RNAs coding for the chlorophyll a/b binding protein and ribulose-1,5-bisphosphate carboxylase) accumulate at a linear rate during 24 hours in darkness following the light pulse. Two transcripts increase rapidly at first but then reach a plateau after 3 hours and remain at that level for the next 21 hours. Another two transcripts exhibit a prolonged lag period before beginning to accumulate, and do not reach significant accumulation rates until 12 to 16 hours after the red light pulse. One transcript appears to undergo a transient increase in abundance in response to red light, but this is superimposed on a background of slowly increasing abundance of this RNA in control plants. This response, unlike all the others, exhibits reciprocity failure in experiments in which the same fluence of light is given over periods ranging between 50 and 4000 seconds.We have also examined the kinetics with which each of these 12 responses escapes from phytochrome-far-red absorbing form control by attempting to reverse the induction with far-red light given at various times after the red light pulse. Again, several different patterns are apparent for the different transcripts. The time at which far red reversibility first begins to be lost, the rate at which it is lost, and the final extent of reversibility remaining after 7 hours in the dark all differ for different transcripts. In addition, we have observed that some responses retain virtually complete photoreversibility for at least 7 hours. In some cases, a comparison of the time course and escape kinetic data indicates that relatively rapid turnover of the RNA must occur. It is not clear whether or not the rate of turnover is influenced by phytochrome.stand more fully the role of phytochrome in developmental regulation it will be necessary to study the responses of a larger number of genes and to determine the extent to which different genes may respond differently to the same stimulus.To this end we have previously isolated and characterized a set of cDNA clones which correspond to cab and rbcS mRNAs as well as 11 as yet unidentified transcripts whose abundance in etiolated pea buds is influenced by light acting through the phytochrome system (16). We have analyzed the fluence ("dose") dependence of these responses (7,9), showing that some transcripts accumulate in response to red light in the very low fluence range (e.g. I0-' gmol m-2) while others respond also, or exclusively, to R3 in the low fluence range (e.g I03 umol m-2). Only the LF responses are reversible with FR, as expected since the amount of Pfr produced by most FR sources is sufficient to saturate the VLF responses (2, 17).In the present study we further characterize ...

Light Effects on Several Chloroplast Components in Norflurazon-Treated Pea Seedlings

“…Transcript levels were similar in herbicide-treated and untreated plants (except Cab, rbcL, and pEA207, where the levels were somewhat higher in the NF-treated plants). Transfer to white light of untreated seedlings produced a dramatic increase in the mRNA in each case except pEA207 where, as expected, there was a decrease (24,38). This reduction in pEA207 mRNA occurred both in control and NF plants, indicating that NF treatment did not affect the accumulation of this transcript.…”

“…Five probes represent nuclear-encoded mRNAs: Cab, Fed I, RbcS, pEA214, pEA207; one, rbcL, is encoded by the chloroplast genome. pEA214 and pEA207 both represent as yet unidentified nuclear-encoded, light-responsive genes (24,38), but whereas RNA levels corresponding to pEA214 increase in light, pEA207 mRNAs decrease in white light as compared to the level in etiolated pea buds.…”

“…pEA2 14 represents an unidentified phytochrome-regulated nuclear gene (24,38). The mRNA corresponding to this cDNA clone shows a low fluence response and increases linearly following a pulse of red light (24). Its sensitivity to the NF treatment suggests that the pEA214 gene product may also be a nuclearencoded protein destined for the chloroplast, since cytosolic proteins and mRNAs do not appear to be affected by NF (32).…”

“…Analyses of the transcription rates in isolated nuclei were inconclusive. pEA2 14 represents an unidentified phytochrome-regulated nuclear gene (24,38). The mRNA corresponding to this cDNA clone shows a low fluence response and increases linearly following a pulse of red light (24).…”

Genetic and molecular analysis of an allelic series of cop1 mutants suggests functional roles for the multiple protein domains.

“…Dark-grown plants are able to initiate photomorphogenesis as soon as they receive light stimuli (Mohr and Shropshire, 1983;Kendrick and Kronenberg, 1986), and this process is extremely rapid. Changes in gene expression occur within minutes of the perception of light signals (Kaufman et al, 1986), and plastids visibly begin chloroplast development within an hour of light perception (Kirk and Tilney-Bassett, 1978).…”