Nuclear Involvement in the Appearance of a Chloroplast-Encoded 32,000 Dalton Thylakoid Membrane Polypeptide Integral to the Photosystem II Complex

Abstract

The genetic locus for the high chlorophyH fluorescent photosystem IIdeficient maize mutant hcfJ-3 has been definitively located to the nuclear genome. Fluorography of lamellar polypeptides labeled with I35Slmethio-nine in vivo revealed the specific loss of a heavily labeled 32,000 dalton thylakoid membrane polypeptide as well as its chloroplast encoded precursor species at 34,000 daltons. Examination of freeze-fractured mesophylH and bundle sheath thylakoids from hcft-3 revealed that both plastid types lacked the large EFs particles believed to consist of the photosystem II reaction center-core complex and associated light harvesting chlorophyllproteins. The present evidence suggests that the synthesis or turnover/ integration of the chloroplast-encoded 34,000 to 32,000 dalton polypeptide is under nuclear control, and that these polyipeptides are integral components of photosystem II which may be required for the assembly or structural stabilization of newly formed photosystem II reaction centers in both mesophyll and bundle sheath chloroplasts.Zea mays is an excellent experimental system for characterizing interactions between the nuclear and chloroplast genomes in higher plants. There is a wealth of information on heritable nuclear traits both from the physiological and genetic points of view in this organism; in addition, recent advances have led to the physical characterization ofmuch ofthe maize chloroplast genome (6).The intemal (thylakoid) membranes of chloroplasts contain more than 40 distinct size classes of intrinsic polypeptides. One of these, a polypeptide exhibiting an apparent mol wt of 32,000 on polyacrylamide gels, has received considerable attention in developmental studies. In several plant species, the 32,000 dalton polypeptide, or its precursor species (see below) is rapidly labeled by isolated chloroplasts (1 1, 13-15), appears to be rapidly turned over in vivo (13,30), and is biosynthetically regulated at the level of transcription (5,11,12,18). Mattoo et al. (21) have compared partial proteolytic digestion patterns of "32,000" dalton polypeptides exhibiting these general characteristics from a number of '

Chlorophyll-Protein Complexes of a Photosystem II Mutant of Maize

“…The presence of a CP complex in LDS-PAGE patterns which migrates in the position of a complex previously assigned to PSII has been listed as evidence that thylakoids of hcf-3 contain the reaction center of PSII (13). We show in this report that the CP band in hcf-3 is not related to CP complexes which have been assigned to PSII.…”

Nuclear mutation leads to an accelerated turnover of chloroplast-encoded 48 kd and 34.5 kd polypeptides in thylakoids lacking photosystem II

“…In wild-type chloroplasts both the newly synthesized 48 kd and the 34.5 kd polypeptides were greatly enriched in grana lamellae (Figure 7), consistent with the preferential localization of photosystem II to stacked membranes. In contrast, most of the newly synthesized 48 kd and 34.5 kd polypeptides were found in the stroma lamellae in hcf*-3, despite the fact that these chloroplasts contain grana stacks (Miles and Daniel, 1974;Leto et al, 1982). Accumulation of both polypeptides in hcf*-3 stroma lamellae was roughly equivalent to that occurring in wild type during this period.…”

“…In addition to the loss of stainable proteins, hcf*-3 thylakoids fail to accumulate prominantly labeled 34-32 kd polypeptides (Leto et al, 1982). As shown in Figure iB, a 34.5 kd polypeptide was the major newly synthesized protein accumulation in wild-type thylakoids when seedlings were pulse labeled with [35S]methionine for 4 h in the light.…”

“…We have examined the mutational loss of thylakoid membrane polypeptides by studying the synthesis and integration of chloroplast-encoded photosystem II reaction center polypeptides in hcf*-3, a nuclear maize mutant lacking photosystem II activity (Miles and Daniel, 1974; Leto and Miles, 1980). This functional loss is accompanied by the physical loss of organized photosystem II reaction centers (Leto et al, 1982), which is apparently due IRL Press Limited, Oxford, England. to the failure of mutant thylakoids to accumulate most or all of the polypeptides known to comprise the reaction center (Metz and Miles, 1982;Leto et al, 1982;Leto, 1984;Metz et al, 1984). Despite these losses, hcf*-3 seedlings are phenotypically green due to their high content of the photosystem II light harvesting chlorophyll-protein complex (Leto and Arntzen, 1981;Leto, 1984;Metz et al, 1984), and activities other than those associated with photosystem II are largely unaffected by the mutation (Miles and Daniel, 1974;Miles, 1975;Leto and Arntzen, 1981).…”

Light-Induced Nuclear Synthesis of Spinach Chloroplast Fructose-1,6-bisphosphatase

“…This is the case of the low mol wt subunit of ribulose-1,5-bisphosphate carboxylase (1 1), plastocyanin, and Fd-NADP+-reductase (15). In addition, some other organelle proteins are synthesized in the chloroplast, but frequently their synthesis is in a way under nuclear control (18).…”