Two short‐chain dehydrogenase/reductases, NON‐YELLOW COLORING 1 and NYC1‐LIKE, are required for chlorophyll b and light‐harvesting complex II degradation during senescence in rice

Abstract

SummaryYellowing, which is related to the degradation of chlorophyll and chlorophyll-protein complexes, is a notable phenomenon during leaf senescence. NON-YELLOW COLORING1 (NYC1) in rice encodes a membrane-localized short-chain dehydrogenase/reductase (SDR) that is thought to represent a chlorophyll b reductase necessary for catalyzing the first step of chlorophyll b degradation. Analysis of the nyc1 mutant, which shows the staygreen phenotype, revealed that chlorophyll b degradation is required for the degradation of light-harvesting complex II and thylakoid grana in leaf senescence. Phylogenetic analysis further revealed the existence of NYC1-LIKE (NOL) as the most closely related protein to NYC1. In the present paper, the nol mutant in rice was also found to show a stay-green phenotype very similar to that of the nyc1 mutant, i.e. the degradation of chlorophyll b was severely inhibited and light-harvesting complex II was selectively retained during senescence, resulting in the retention of thylakoid grana even at a late stage of senescence. The nyc1 nol double mutant did not show prominent enhancement of inhibition of chlorophyll degradation. NOL was localized on the stromal side of the thylakoid membrane despite the lack of a transmembrane domain. Immunoprecipitation analysis revealed that NOL and NYC1 interact physically in vitro. These observations suggest that NOL and NYC1 are co-localized in the thylakoid membrane and act in the form of a complex as a chlorophyll b reductase in rice.

Pheophytin Pheophorbide Hydrolase (Pheophytinase) Is Involved in Chlorophyll Breakdown during Leaf Senescence in Arabidopsis

“…It was suggested that decreasing the chlorophyll b portion in the chlorophyll-protein complexes of the photosystems causes their destabilization (Horn and Paulsen, 2004) and could trigger both apoprotein and chlorophyll degradation (Rü diger, 2002;Hö rtensteiner, 2006). This was corroborated recently by cloning of NON-YELLOW COLORING1 (NYC1) and NYC1-LIKE (NOL) Sato et al, 2009). NYC1 and NOL encode two subunits of chlorophyll b reductase (Sato et al, 2009), which catalyzes the first half of chlorophyll b to chlorophyll a reduction, i.e., conversion of chlorophyll b to 7-hydoxymethyl chlorophyll a. nyc1 and nol mutants stay green during senescence and thereby selectively retain photosystem II (PSII) light-harvesting complex subunits (LHCII) and exhibit particularly high concentrations of chlorophyll b.…”

Chlorophyll b degradation by chlorophyll b reductase under high-light conditions

“…Although the phenotypes of CBR-deficient mutants during senescence have been studied (Kusaba et al 2007;Horie et al 2009;Sato et al 2009), the effect of the light conditions on the degradation activity of chlorophyll b has not yet been determined. In this report, we analyzed mutant plants that are defective in chlorophyll b degradation under a high-light treatment to elucidate the role of chlorophyll b degradation in the regulation of the light-harvesting system.…”

Mendel’s Genes: Toward a Full Molecular Characterization

“…While it is clear that it is involved with the chlorophyll catabolic pathway, the absence of known domains has made it difficult to deduce a function from the gene sequence (Aubry et al 2008;Sato et al 2009). …”