Abstract
Chlorophyll (Chl) synthase catalyzes esterification of chlorophyllide to complete the last step of Chl biosynthesis. Although the Chl synthases and the corresponding genes from various organisms have been well characterized, Chl synthase mutants have not yet been reported in higher plants. In this study, a rice (Oryza Sativa) Chl-deficient mutant, yellow-green leaf1 (ygl1), was isolated, which showed yellow-green leaves in young plants with decreased Chl synthesis, increased level of tetrapyrrole intermediates, and delayed chloroplast development. Genetic analysis demonstrated that the phenotype of ygl1 was caused by a recessive mutation in a nuclear gene. The ygl1 locus was mapped to chromosome 5 and isolated by map-based cloning. Sequence analysis revealed that it encodes the Chl synthase and its identity was verified by transgenic complementation. A missense mutation was found in a highly conserved residue of YGL1 in the ygl1 mutant, resulting in reduction of the enzymatic activity. YGL1 is constitutively expressed in all tissues, and its expression is not significantly affected in the ygl1 mutant. Interestingly, the mRNA expression of the cab1R gene encoding the Chl a/b-binding protein was severely suppressed in the ygl1 mutant. Moreover, the expression of some nuclear genes associated with Chl biosynthesis or chloroplast development was also affected in ygl1 seedlings. These results indicate that the expression of nuclear genes encoding various chloroplast proteins might be feedback regulated by the level of Chl or Chl precursors.
Highlights
Chlorophyll (Chl) synthase catalyzes esterification of chlorophyllide to complete the last step of Chl biosynthesis
Directed mutational analysis with a photosynthetic bacterium, Rhodobacter capsulatus, provided abundant information on the genes involved in bacteriochlorophyll biosynthesis (Bollivar et al, 1994b), and homologous genes have been isolated from oxygenic plants (Jensen et al, 1996)
Detailed investigations of the properties of Chl synthase became feasible after demonstrating that the bacteriochlorophyll synthase gene of R. capsulatus encodes bacteriochlorophyll synthase (Bollivar et al, 1994b)
Summary
Chlorophyll (Chl) synthase catalyzes esterification of chlorophyllide to complete the last step of Chl biosynthesis. Chlorophyll (Chl) molecules universally exist in photosynthetic organisms They perform essential processes of harvesting light energy in the antenna systems and driving electron transfer in the reaction centers (Fromme et al, 2003). Chl synthase is believed to be bound to the thylakoid membranes and to catalyze prenylation of chlorophyllide (Chlide) with geranygeranyl diphosphate (GGPP) or phytyl diphosphate (PhyPP), the last step of Chl biosynthesis (Rudiger et al, 1980; Soll and Schultz, 1981; Soll et al, 1983). This step is essential for the accumulation of Chl a (Eichacker et al, 1990, 1992) and Random sequence analysis of EST cDNAs from rice (Oryza sativa) yielded a putative Chl synthase homolog (Lopez et al, 1996; Scolnik and Bartley, 1996), the biochemical properties and physiological functions remain unknown
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