DIFFERENTIAL REGULATION OF CHLOROPLAST GENE-EXPRESSION IN CHLAMYDOMONAS-REINHARDTII DURING PHOTOACCLIMATION - LIGHT STRESS TRANSIENTLY SUPPRESSES SYNTHESIS OF THE RUBISCO LSU PROTEIN WHILE ENHANCING SYNTHESIS OF THE PS-II D1 PROTEIN
M. Shapira et al., DIFFERENTIAL REGULATION OF CHLOROPLAST GENE-EXPRESSION IN CHLAMYDOMONAS-REINHARDTII DURING PHOTOACCLIMATION - LIGHT STRESS TRANSIENTLY SUPPRESSES SYNTHESIS OF THE RUBISCO LSU PROTEIN WHILE ENHANCING SYNTHESIS OF THE PS-II D1 PROTEIN, Plant molecular biology, 33(6), 1997, pp. 1001-1011
Transfer of Chlamydomonas reinhardtii cells grown photoautotrophically
in low light to higher light intensities has a dramatic transient eff
ect on the differential expression of the two major chloroplast encode
d photosynthetic proteins. Synthesis of the D1 protein of Photosystem
II increases more than 10-fold during the first six hours in high ligh
t (HL), whereas synthesis of the large subunit (LSU) of Rubisco drops
dramatically within 15 min and only gradually resumes at about 6 h. Sy
nthesis of the chloroplast-encoded ATP synthase beta subunit, the nucl
ear-encoded Rubisco small subunit and the nuclear-encoded beta-tubulin
is not noticeably affected. Up regulation of psbA mRNA translation ac
counts for a substantial fraction of the increased Di synthesis, since
accumulation of psbA mRNA increases 4.2- and 6.3-fold less than D1 sy
nthesis at 6 and 18 h in HL. Down-regulation of LSU synthesis is not c
orrelated with a reduction in the steady-state level of the rbcL trans
cript. Primer extension mapping of the 5' ends of the rbcL mRNAs revea
ls transcripts with start points located at -93 and -168 relative to t
he first translated ATG. Transfer of low light (LL)-grown cells to HL
temporarily decreases the ratio of the -93 to -168 transcripts, but th
is ratio normalizes after 6 h in HL, coincident with the recovery in t
he synthesis of LSU. These several distinct effects of temporary Light
stress were correlated with a rapid, sustained increase in the reduct
ion state of Q(A), a transient decline in photosynthetic efficiency, a
less rapid drop in total chlorophyll content and a delay in cell divi
sion.