Identification of the 7-hydroxymethyl Chlorophyll a Reductase of the Chlorophyll Cycle in Arabidopsis

Plant Cell. 2011 Sep;23(9):3442-53. doi: 10.1105/tpc.111.089714. Epub 2011 Sep 20.


The interconversion of chlorophyll a and chlorophyll b, referred to as the chlorophyll cycle, plays a crucial role in the processes of greening, acclimation to light intensity, and senescence. The chlorophyll cycle consists of three reactions: the conversions of chlorophyll a to chlorophyll b by chlorophyllide a oxygenase, chlorophyll b to 7-hydroxymethyl chlorophyll a by chlorophyll b reductase, and 7-hydroxymethyl chlorophyll a to chlorophyll a by 7-hydroxymethyl chlorophyll a reductase. We identified 7-hydroxymethyl chlorophyll a reductase, which is the last remaining unidentified enzyme of the chlorophyll cycle, from Arabidopsis thaliana by genetic and biochemical methods. Recombinant 7-hydroxymethyl chlorophyll a reductase converted 7-hydroxymethyl chlorophyll a to chlorophyll a using ferredoxin. Both sequence and biochemical analyses showed that 7-hydroxymethyl chlorophyll a reductase contains flavin adenine dinucleotide and an iron-sulfur center. In addition, a phylogenetic analysis elucidated the evolution of 7-hydroxymethyl chlorophyll a reductase from divinyl chlorophyllide vinyl reductase. A mutant lacking 7-hydroxymethyl chlorophyll a reductase was found to accumulate 7-hydroxymethyl chlorophyll a and pheophorbide a. Furthermore, this accumulation of pheophorbide a in the mutant was rescued by the inactivation of the chlorophyll b reductase gene. The downregulation of pheophorbide a oxygenase activity is discussed in relation to 7-hydroxymethyl chlorophyll a accumulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis / physiology
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Chlorophyll / analogs & derivatives*
  • Chlorophyll / metabolism
  • Chlorophyll A
  • Ferredoxins / metabolism
  • Gene Expression Regulation, Plant
  • Iron-Sulfur Proteins / genetics
  • Iron-Sulfur Proteins / metabolism*
  • Molecular Sequence Data
  • Mutation
  • Oxidoreductases / genetics
  • Oxidoreductases / metabolism*
  • Phylogeny
  • Sequence Alignment


  • 7-hydroxymethyl chlorophyll
  • Arabidopsis Proteins
  • Ferredoxins
  • Iron-Sulfur Proteins
  • Chlorophyll
  • 7-hydroxymethyl chlorophyll a reductase, Arabidopsis
  • Oxidoreductases
  • Chlorophyll A