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Chlorophyll Degradation and Light-harvesting Complex II Aggregate Formation During Dark-induced Leaf Senescence in Arabidopsis Pheophytinase Mutants

Yang, Young Nam, Safarova, Rana B., Park, So-Yon, Sakuraba, Yasuhito, Oh, Min-Hyuk, Zulfugarov, Ismayil S., Lee, Chin Bum, Tanaka, Ayumi, Paek, Nam-Chon, Lee, Choon-Hwan
Journal of plant biology 2019 v.62 no.1 pp. 27-38
Arabidopsis thaliana, chlorophyll, genes, leaves, light harvesting complex, mutants, thylakoids
The stay-green mutant of Arabidopsis thaliana, ore10 forms stable light-harvesting complex II (LHCII) aggregates during dark-induced senescence, which showed a single base deletion (G1351) in the coding region of the pheophytinase (PPH) gene. PPH specifically dephytylates the Mg-free chlorophyll (Chl) pigment pheophytin, yielding pheophorbide. In both ore10 and pph-1 mutants, pheophytin a accumulated due to the deficiency of PPH gene, but the amount was relatively smaller than that of degraded Chl, and most of the pheophytin a was bound to the stable LHCII forming aggregates with some other Chl-protein (CP) complexes. Comparison of Chl a/b ratios in thylakoids, aggregates, and LHCII indicated that the suppression of Chl b to Chl a conversion was stronger when Chl b reductase was missing and weak when PPH is missing in the large Chl catabolic complex, which allowed the partial degradation of Chl b. These results suggest that the PPH-dependent pathway is not specific for LHCII, but common for all CP complexes, including LHCII. In PPH-deficient mutants, the degradation of LHCII was suppressed by the formation of aggregates, and some of the remaining CP complexes and pheophytin a were included in the aggregates. Non-included CP complexes were degraded via an unknown mechanism.