GENETIC CONTROL OF CHLOROPHYLL BIOSYNTHESIS IN CHLAMYDOMONAS

Abstract

In this report we describe two nonallelic Mendelian protoporphyrin accumulating mutants brs-I and bre-1. Results of experiments with these mutants lead us to postulate that porphyrin biosynthesis branches into light and dark steps between protoporphyrin-IX and magnesium protoporphyrin. We hypothesize that the br e locus controls a dark step while the br s locus either controls a step in the main pathway before the branch or mediates the preparation of the magnesium ion for its insertion into protoporphyrin-IX. The brs-1 mutant is thought to be light sensitive because a block prior to the branch point in the porphyrin pathway prevents chlorophyll formation in either the light or the dark. The brc-1 mutant, which also accumulates protoporphyrin in the dark, forms chlorophyll and chloroplast lamellae when transferred to the light, showing that function of the porphyrin pathway is normal in the light.

Kinetics and regulation of synthesis of the major polypeptides of thylakoid membranes in Chlamydomonas reinhardtii y-1 at elevated temperatures

“…The spectral requirement for the production of these polypeptides coincides with that for chlorophyll synthesis, suggesting that synthesis of chlorophyll in some manner controls synthesis of the polypeptides. This suggestion is supported by the observation that wild type cells, which synthesize chlorophyll in the dark (24,49), also are capable of making b and c in the dark. However, since the site of synthesis of chlorophyll is within chloroplasts (42,43), a mechanism by which synthesis ofb and c on cytoplasmic ribosomes can be controlled by chlorophyll or its precursors is not obvious.…”

“…Cells of wild type C. reinhardtii (strain 137c) do not need light to synthesize chlorophyll, and so remain green when grown in the dark (24,49). To determine whether synthesis of b and c is dependent upon a direct involvement of light or, rather, upon the synthesis of chlorophyll, wild type cells were tested for their ability to make b and c in light or dark at 38~ Under conditions identical to those of experiments described for C. reinhardtii y-1 cells, wild type cells were labeled with…”

LTS3 gene controls light-independent chlorophyll biosynthesis in green algae Chlamydomonas reinhardtii

“…Подобный эффект описан и для мутантов yellow (Wang et al, 1974). В обоих случаях, эти данные можно объяснить наличием в клетках мутан-тов протохлорофиллида -ретроингибитора синтеза АЛК (Timko, 1998;Armstrong, 1998).…”

“…Их клетки, выращенные в темноте, содержат около 8 % хлорофил-ла. После освещения этот уровень несколько снижается, вместе с уменьшением уровня ПП (Wang et al, 1974), а затем начинает медленно возрастать после 48 часов пре-бывания на свету в культурах штамма lts3 и 72 часов -у brc-1. Далее, кинетика синтеза хлорофилла становить-ся сходной с таковой у клеток y-7.…”

“…Подобные мутанты: brc-1 и brc-2 были описаны в США Энди Вангом (Wang et al, 1974) как штаммы, несущие рецессивные, аллельные мутации, которые генетически и функционально отличаются от мутации y-1, блокиру-ющей темновое превращение ПХЛД. Поскольку двойной мутант генотипа: brc-1, y-1 имел фенотип штамма brc-1, автор предположил, что локус «Brc» контролирует более ранний, чем конверсия ПХЛД, шаг биосинтетического пути.…”