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

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.

Beyond pathways: genetic dissection of tocopherol content in maize kernels by combining linkage and association analyses

“…In pepper fruit, a QTL controlling chlorophyll content was shown to have altered tocopherol content (Brand et al, 2012). In Arabidopsis, changes in the expression of a gene encoding chlorophyll synthase affect tocopherol levels (Zhang et al, 2015). Similarly, vte5 (encoding phytol kinase) and vte6 (encoding phytyl-phosphate kinase) mutants exhibit reduced tocopherol content (Dorp et al, 2015;Valentin et al, 2006).…”

An allele of ZmPORB2 encoding a protochlorophyllide oxidoreductase promotes tocopherol accumulation in both leaves and kernels of maize

“…We also examined the expression levels of some core genes involved in the vitamin E biosynthesis pathway (VTE2, VTE4, VTE5) and one important for chlorophyll synthesis (CHLG), which was reported to affect tocopherol synthesis in Arabidopsis (Zhang et al, 2015). CHLG expression started to rise when ZmPORB2 expression sharply increased in the P-Leaves but not in the NP-Leaves.…”

“…Recently, chlorophyllase (CLH1, CLH2) and PPH were found to be dispensable for tocopherol accumulation in seed during chlorophyll breakdown (Zhang et al, 2014). However, chlorophyll synthase (CHLG) may affect chlorophyll and tocopherol synthesis in Arabidopsis (Zhang et al, 2015). Recent studies have suggested that chlorophyll dephyty-lase1 (CLD1) has chlorophyll de-phytylation activity that can, in combination with CHLG, form a salvage cycle of chlorophyll turnover (Lin et al, 2014(Lin et al, , 2016 (Figure 1).…”

Agronomic performance of sesame (Sesamum indicum L.) genotypes under phytostimulant application

“…Results of the chlorophyll A content (Tables 5), chlorophyll B content (Table 6) and grain yield (table 8) show that there is a relationship between chlorophyll content and increased productivity when Stimulate ® is applied. The presence of chlorophyll is related to photosynthetic activity, which is responsible for the generation of energy and carbohydrates (ZHANG et al, 2015), which contributes directly to the increase of grain production. However, this increase in productivity varied among the different genotypes according to the crop year.…”