Chlorophyll regulates accumulation of the plastid-encoded chlorophyll apoproteins CP43 and D1 by increasing apoprotein stability.
Chlorophyll apoprotein accumulation in higher plant chloroplasts is controlled by light-dependent chlorophyll formation. Dark-grown plants lack chlorophyll and chlorophyll apoproteins. However, the plastid genes encoding the chlorophyll apoproteins are transcribed; chlorophyll apoprotein mRNA accumulates and associates with polysomes in plastids of dark-grown plants. Pulse-labeling assays revealed a population of short-lived proteins in plastids of dark-grown plants. One of these transiently labeled proteins was CP43, a chlorophyll apoprotein associated with photosystem II. Pulse-chase assays showed that newly synthesized CP43 was rapidly degraded in plastids of dark-grown plants, which lack chlorophyll. In contrast, CP43 synthesized in plastids from illuminated plants was stable. The synthesis of D1, a chlorophyll apoprotein of the photosystem II reaction center, was also analyzed in plastids of dark-grown and illuminated plants. Radiolabel accumulation into full-length D1 was only detected in plastids of illuminated plants. However, D1 translation intermediates of 15-25 kDa were detected in both plastid populations. Pulse-chase assays showed that the 15- to 25-kDa D1 translation products were precursors of mature D1 in plastids of illuminated plants. In contrast, in plastids of dark-grown plants, the 15- to 25-kDa translation intermediates were converted into a 23-kDa polypeptide previously suggested to be a proteolytic product of D1. These results indicate that chlorophyll produced in illuminated plants stabilizes D1 nascent polypeptides, which allows accumulation of mature D1.
Mullet
J E
JE
Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843-2128.
Klein
P G
PG
Klein
R R
RR
D001059:Apoproteins / Q000378:metabolism; D002734:Chlorophyll / Q000502:physiology*; D002736:Chloroplasts / Q000378:metabolism*; D003624:Darkness; D015870:Gene Expression; D001467:Hordeum; D008027:Light; D008970:Molecular Weight; D010940:Plant Proteins / Q000096:biosynthesis / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism; D011233:Precipitin Tests; D012333:RNA, Messenger / Q000235:genetics
D001059:Apoproteins; D010940:Plant Proteins; D012333:RNA, Messenger; D002734:Chlorophyll