Light regulation of the 22 kd heat shock gene transcription and its translation product accumulation in Chlamydomonas reinhardtii.

Abstract

Expression of the nuclear coded heat shock protein HSP22 in Chlamydomonas reinhardtii y‐1 cells is light regulated at the level of transcript accumulation. In dark grown cells, containing a non‐differentiated plastid, light has an additional regulatory effect on the accumulation of HSP22. When such cells are exposed to heat stress in the light, poly(A)+ RNA hybridizing with the HS22 probe is synthesized at levels comparable with those found in cells pre‐illuminated for 3 h (greening) prior to the heat shock. However, this RNA is poorly translated in vitro and HSP22 does not accumulate in vivo. HS22 mRNA efficiently translated in vitro is induced in dark grown cells only when chloroplast differentiation has been initiated by exposure to the light for 3 h. In these cells HSP22 accumulates during heat shock. Inhibition of plastid translation activity during light‐dependent chloroplast development prevents accumulation of HSP22 in vivo. However the HS22 mRNA formed in this case can be efficiently translated in vitro. Light requirement for the accumulation of HSP22 during heat stress is exhibited also by wild type C. reinhardtii cells which possess a differentiated chloroplast irrespective of the light conditions during cell growth. However dark grown wild type cells do not require pre‐illumination for developing the ability to accumulate HSP22 during heat stress in the light.

Insights into the Survival of Chlamydomonas reinhardtii during Sulfur Starvation Based on Microarray Analysis of Gene Expression

“…For example, the sac1 mutant exhibits a dramatic increase in transcripts encoding two putative chloroplast 22-kDa heat shock proteins (18); the increase in transcripts encoding these polypeptides in CC425 is much less pronounced. This type of chaperone is involved in preventing protein denaturation and aggregation in plastids.…”

Accumulation of plastid HSP 23 of Chenopodium rubrum is controlled post‐translationally by light

“…Other indirect evidence stems from the observation that the induction of a plastid-related HSP in Chlamydomonas reinhardtii is controlled by light both at the transcription and post-transcription levels of gene expression (Ish-Shalom et al, 1990). Also, in barley light exerts an effect on the levels of accumulated HSP (Stapel et a/., 1993).…”

Structure and Light-Induced Expression of a Small Heat-Shock Protein Gene of Pharbitis nil

“…An end-labeled oligonucleotide, complimentary to an 18-base stretch of the coding strand (5'-CAGCAGCGCGCCTTCTCG-3', residues 574 to 591, Fig. 4A) was hybridized to 10 ,ug of total RNA isolated from heatshocked or nonheat-shocked P. nil cotyledons at 420C for 14 h. The primer was extended using unlabeled deoxynucleotides and murine leukemia virus reverse transcriptase (BRL). The resulting DNA product was analyzed on a denaturing urea-polyacrylamide sequencing gel.…”

“…Recent studies indicate that the nuclear-encoded hsp22, a chloroplast-associated hsp, and hsp7O in Chlamydomonas are regulated by light at the level of transcript accumulation (11,14). In pea, under heat-shock conditions, the abundance of mRNA corresponding to some low molecular mass hsps was found to vary during the day, indicating a circadian control of their accumulation (20).…”