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​1. Chlorophyll degradation by multi-protein complex of chlorophyll catabolic enzymes

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 Plant leaves become yellow since "chlorophyll" is degraded to colorless linear tetrapyrroles.

 To date, seven chlorophyll catabolic enzymes (CCEs), NONYELLOW COLORING1 (NYC1), NYC1-LIKE (NOL), 7-hydroxymethyl a reductase (HCAR), STAY-GREEN (SGR), pheophytinase (PPH), pheophorbide a oxygenase (PAO), and red chlorophyll catabolite reductase (RCCR), have been identified; these enzymes catalyze the stepwise degradation of chlorophyll to a fluorescent intermediate, pFCC, which is then exported from the plastid. In addition, Senescence-induced SGR binds to light-harvesting complex II (LHCII), but its exact role remains elusive. We revealed that CCEs also specifically interact with LHCII. In addition, CCEs interact directly or indirectly with each other at LHCII, and SGR is essential for recruiting CCEs in senescing chloroplasts. These data indicate a predominant role for the CCE-LHCII protein interaction in the breakdown of LHCII-located chlorophyll, likely to allow metabolic channeling of phototoxic chlorophyll breakdown intermediates upstream of nontoxic pFCC.

<Related publications>

Sakuraba Y, Schelbert S, Park SY, Han SH, Lee BD, Andres CB, Kessler F, Hortensteiner S, Paek NC. (2012) STAY-GREEN and chlorophyll catabolic enzymes interact at light-harvesting complex II for chlorophyll detoxification during leaf senescence in Arabidopsis. The Plant Cell 24:507-518. 

Sakuraba Y, Kim YS, Yoo SC, Hortensteiner S, Paek NC. (2013) 7-Hydroxymethyl chlorophyll a reductase functions in metabolic channeling of chlorophyll breakdown intermediates during leaf senescence. Biochemical. Biophysical. Research Commnications. 430:32-37. 

Sakuraba Y, Park SY, Kim YS, Wang SH, Yoo SC, Hortensteiner S, Paek NC. (2014) Arabidopsis STAY-GREEN2 is a Negative Regulator of Chlorophyll Degradation during Leaf Senescence. Molecular Plant 7:1288-1302.

Sakuraba Y*, Kim D, Kim YS, Hortensteiner S, Paek NC. (2014) Arabidopsis STAYGREEN-LIKE (SGRL) promotes abiotic stress-induced leaf yellowing during vegetative growth. FEBS Letters 3;588:3830-3837.

Sakuraba Y, Park SY, Paek NC. (2015) The Divergent Roles of STAYGREEN (SGR) Homologs in Chlorophyll Degdation. Mol. Cells, 38:390-395. Review

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