Protein Degradation

Apel

Molecular and Cellular Biology

1995

The NADPH:protochlorophyllide oxidoreductase precursor protein (pPorA) of barley (Hordeum vulgare L. cv. Carina), synthesized from a full-length cDNA clone by coupling in vitro transcription and translation, is a catalytically active protein. It converts protochlorophyllide to chlorophyllide in a light-and NADPH-dependent manner. At least the pigment product of catalysis remains tightly bound to the precursor protein. The chlorophyllide-pPorA complex differs markedly from the protochlorophyllide-pPorA complex with respect to sensitivity to attack by a light-induced, nucleus-encoded, and energy-dependent protease activity of barley plastids. The pPorA-chlorophyllide complex is rapidly degraded, in contrast to pPorA-protochlorophyllide complexes containing or lacking NADPH, which are both resistant to protease treatment. Unexpectedly, pPorA devoid of its substrates or products was less sensitive to proteolysis than the pPorA-chlorophyllide complex, suggesting that both substrate binding and product formation during catalysis had caused differential changes in protein conformation.

“…However, only a very few protease activities have been identified in plants thus far (31,55). In particular, little is known about plastid-specific proteases.…”

Section: Discussionmentioning

confidence: 99%

A Light-Induced Protease from Barley Plastids Degrades NADPH:Protochlorophyllide Oxidoreductase Complexed with Chlorophyllide

Apel

Molecular and Cellular Biology

1995

“…In oat leaves an acid endopeptidase has been located in the vacuoie and the apoplast, while a neutral endopeptidase has been found outside the vacuoie in a compartment which is yet to be identified (van der Valk & van Loon, 1988). Matile (1982) has suggested that vacuoles act as lysosomes in plant cells and degrade proteins after invagination of the cytoplasm. However, he does not discount the possibility that chloroplasts may contain their own proteases.…”

Section: Vacunlementioning

confidence: 99%

Gene expression during leaf senescence

1994

SUMMARY Leaf senescence is a hiphly‐controlled sequence of events comprising the final stage of development. Cells remain viable during the process and new gene expression is required. There is some similarity between senescence in plants and programmed cell death in animals. In this review, different classes of senescence‐related genes are defined and progress towards isolating such genes is reported. A range of internal and external factors which appear to cause leaf senescence is considered and various models for the mechanism of senescence‐ initiation are described. The current understanding of senescence at the wrganelle and molecular levels is presented. Finally, same ideas are mooted as to why senescence occurs and why it should be studied further.

“…{b) Intracellular location. Endoproteolytic activities of leaf cells from many plant species are located mainly in vacuoles (Boiler & Kende, 1979;Heck, Martinoia & Matile, 1981-Lin & Wittenbach, 1981Matile, 1982;Waters et al, 1982;Wittenbach, Lin & Hebert, 1982;Thayer & Huffaker, 1984;Boiler & Wiemken, 1986). The two main EPs of barley leaves (Miller & Huffaker, 1981) were predominantly localized in vacuoles isolated from barley leaves (Thayer & Huffaker, 1984).…”

Section: Substratesmentioning

confidence: 99%

Proteolytic activity during senescence of plants

Huffaker

1990

New Phytologist

155

summary Although information has rapidly developed concerning the intracellular localization of plant proteins, relatively few reports concern the intracellular location of endo‐ and exo‐proteolytic activities. Relatively few proteases have been purified, characterized, and associated with a specific cellular location. With the exception of the processing proteases involved in transport of proteins across membranes, little progress has yet been made concerning determination of in vivo products of specific proteases. Information on the turnover of individual proteins and the assessment of rate‐limiting steps in pathways as proteins are turned over is steadily appearing. Since chloroplasts are the major site of both protein synthesis and, during senescence, degradation, it was important to show unambiguously that chloroplasts can degrade their own constituents. Another important contribution was to obtain evidence that the chloroplasts contain proteases capable of degrading their constituents. This work has been more tenuous because of the low activities found and the possibility of contamination by vacuolar enzymes during the isolation of organelles. The possible targeting of cytoplasmic proteins for degradation by facilitating their transport into vacuoles is a field which hopefully will develop more rapidly in the future. Information on targeting of proteins for degradation via the ubiquitin (Ub) degradation pathway is developing rapidly. Future research must determine how much unity exists across the different eukaryotic systems. At present, it has important implications for protein turnover in plants, since apparently Ub is involved in the degradation of phytochrome. Little information has been developed regarding what triggers increased proteolysis with the onset of senescence, although it appears to involve protein synthesis. Thus far, the evidence indicates that the complement of proteases prior to senescence is sufficient to carry out the observed protein degradation. This field of study has great practical implications, e.g. maintaining photosynthesis during seed‐fill in order to obtain greater crop yields. The current use of ‘stay green’ variants in the populations of several crop plants to produce increased yields shows the potential for future development. The near future should see exciting discoveries in these areas of research that will have far reaching effects on the construction of transgenic plants for future research accomplishments and agricultural use.