Chlorophyll Synthase under Epigenetic Surveillance Is Critical for Vitamin E Synthesis, and Altered Expression Affects Tocopherol Levels in Arabidopsis

Authors

Chunyu Zhang, University of Nebraska-LincolnFollow
Wei Zhang, Huazhong Agricultural University
Guodong Ren, University of Nebraska - Lincoln
Denli Li, Huazhong Agricultural University
Rebecca E. Cahoon, University of Nebraska-LincolnFollow
Ming Chen, University of Nebraska - Lincoln
Yongming Zhou, Huazhong Agricultural UniversityFollow
Bin Yu, University of Nebraska - LincolnFollow
Edgar B. Cahoon, University of Nebraska - LincolnFollow

Date of this Version

8-2015

Citation

Plant Physiology, August 2015, Vol. 168, pp. 1503–1511.

Comments

Copyright 2015 American Society of Plant Biologists. All Rights Reserved.

Abstract

Chlorophyll synthase catalyzes the final step in chlorophyll biosynthesis: the esterification of chlorophyllide with either geranylgeranyl diphosphate or phytyl diphosphate (PDP). Recent studies have pointed to the involvement of chlorophyll-linked reduction of geranylgeranyl by geranylgeranyl reductase as a major pathway for the synthesis of the PDP precursor of tocopherols. This indirect pathway of PDP synthesis suggests a key role of chlorophyll synthase in tocopherol production to generate the geranylgeranyl-chlorophyll substrate for geranylgeranyl reductase. In this study, contributions of chlorophyll synthase to tocopherol formation in Arabidopsis (Arabidopsis thaliana) were explored by disrupting and altering expression of the corresponding gene CHLOROPHYLL SYNTHASE (CHLSYN; At3g51820). Leaves from the homozygous chlysyn1-1 null mutant were nearly devoid of tocopherols, whereas seeds contained only approximately 25% of wild-type tocopherol levels. Leaves of RNA interference lines with partial suppression of CHLSYN displayed marked reductions in chlorophyll but up to a 2-fold increase in tocopherol concentrations. Cauliflower mosaic virus35S-mediated overexpression of CHLSYN unexpectedly caused a cosuppression phenotype at high frequencies accompanied by strongly reduced chlorophyll content and increased tocopherol levels. This phenotype and the associated detection of CHLSYN-derived small interfering RNAs were reversed with CHLSYN overexpression in rna-directed rna polymerase6 (rdr6), which is defective in RNA-dependent RNA polymerase6, a key enzyme in sense transgene-induced small interfering RNA production. CHLSYN overexpression in rdr6 had little effect on chlorophyll content but resulted in up to a 30% reduction in tocopherol levels in leaves. These findings show that altered CHLSYN expression impacts tocopherol levels and also, show a strong epigenetic surveillance of CHLSYN to control chlorophyll and tocopherol synthesis.