A Novel Role of Water-Soluble Chlorophyll Proteins in the Transitory Storage of Chorophyllide  

Abstract

All chlorophyll (Chl)-binding proteins involved in photosynthesis of higher plants are hydrophobic membrane proteins integrated into the thylakoids. However, a different category of Chl-binding proteins, the so-called water-soluble Chl proteins (WSCPs), was found in members of the Brassicaceae, Polygonaceae, Chenopodiaceae, and Amaranthaceae families. WSCPs from different plant species bind Chl a and Chl b in different ratios. Some members of the WSCP family are induced after drought and heat stress as well as leaf detachment. It has been proposed that this group of proteins might have a physiological function in the Chl degradation pathway. We demonstrate here that a protein that shared sequence homology to WSCPs accumulated in etiolated barley (Hordeum vulgare) seedlings exposed to light for 2 h. The novel 22-kD protein was attached to the outer envelope of barley etiochloroplasts, and import of the 27-kD precursor was light dependent and induced after feeding the isolated plastids the tetrapyrrole precursor 5-aminolevulinic acid. HPLC analyses and spectroscopic pigment measurements of acetone-extracted pigments showed that the 22-kD protein is complexed with chlorophyllide. We propose a novel role of WSCPs as pigment carriers operating during light-induced chloroplast development.In light-grown seedlings and mature green plants, chlorophyll (Chl) a and Chl b as well as carotenoids are bound to various proteins within PSI and PSII (Ort and Yocum, 1996). These proteins differ in their Chlbinding properties: one group binds only Chl a, whereas the other can bind both Chl a and Chl b (for reviews, see von Wettstein et al., 1995;Green and Durnford, 1996). The first group is represented by the plastid-encoded pigment-binding proteins of the actual reaction centers (PSI-A/B and D1/D2 in PSII) and the photosynthetic cores of PSII (CP43 and CP47).The second group comprises the light-harvesting Chl a/b-binding proteins LHCI and LHCII of PSI and PSII, respectively (Dreyfuss and Thornber, 1994;Kü hlbrandt et al., 1994;Green and Durnford, 1996). These nuclear gene products form the outer antenna complexes of the two photosystems. The Chl content of LHCII accounts for approximately 50% of all Chls in the thylakoid membranes (Kü hlbrandt et al., 1994). LHCII operates as a trimer (Dreyfuss and Thornber, 1994), and each monomer contains Chl a plus Chl b in a 7:6 stoichiometry (Kü hlbrandt et al., 1994). Monomeric LHCII is embedded into the thylakoids via three a-helices (Kü hlbrandt et al., 1994). Similar, structurally related a-helices also occur in other Chl-binding proteins, such as the minor light-harvesting Chl a/bbinding proteins CP29, CP26, CP24, and CP14 (summarized in Green et al., 1991;Jansson, 1994; Paulsen, 1995), and the early light-inducible proteins (ELIPs; Kloppstech et al., 1984;Grimm and Kloppstech, 1987;Grimm et al., 1989; for review, see Adamska, 1997). The S-subunit of PSII (PsbS) is a related but four-helix Chl-binding protein, which contains an additional fourth helix similar to helix 2 present in LHC...

The Senescence-Induced Staygreen Protein Regulates Chlorophyll Degradation

“…Satoh et al (1998) proposed the water-soluble chlorophyll protein (WSCP) as a feasible candidate for a Chl carrier. However, a recent report indicated that WSCP might act as a Chlide transporter during periods of increased Chl synthesis in developing leaves rather than during Chl degradation in senescing leaves (Reinbothe et al, 2004). In higher plants, Chlorophyllase (CLH) genes encode soluble proteins that are predicted to localize in the cytoplasm, vacuole, or chloroplast stroma (Tsuchiya et al, 1999;Takamiya et al, 2000;Okazawa et al, 2006).…”

Nitric Oxide Signaling During Senescence and Programmed Cell Death in Leaves

“…Satoh et al (1998) proposed the water-soluble chlorophyll protein (WSCP) as a feasible candidate for a Chl carrier. However, a recent report indicated that WSCP might act as a Chlide transporter during Chl synthesis in developing leaves rather than during Chl degradation in senescing leaves (Reinbothe et al, 2004). In higher plants, Chlorophyllase (CLH) genes encode soluble proteins that are predicted to localize in the cytoplasm, vacuole, or chloroplast stroma (Tsuchiya et al, 1999;Takamiya et al, 2000;Okazawa et al, 2006).…”

LHPP, the light-harvesting NADPH:protochlorophyllide (Pchlide) oxidoreductase:Pchlide complex of etiolated plants, is developmentally expressed across the barley leaf gradient

“…A water-soluble chlorophyll protein (WSCP) was recently discovered for barley etiochloroplasts [52] that displays similarity to WSCPs of Brassicaceae [41]. Interestingly, in cauliflower WSCPs bind both Chl a and Chl b but exhibited pigment fluorescence at 680 nm only when present in a homo-oligomeric state [41].…”

“…barley WSCP is a nucleus-encoded plastid protein which is synthesized as a 27 kDa precursor. Import into the plastid occurs under conditions when Chlide is produced, and the 27 kDa precursor is processed to mature size of 22 kDa [52].…”

“…Immunological studies were performed with a heterologous antiserum against Lepidium virginicum WSCP to which the barley homolog is most related [52]. Fig.…”