Advances in understanding of the primary reactions of protochlorophyll(ide) photoreduction in cells and model systems

The key step in chlorophyll biosynthesis is photoreduction of its immediate precursor, protochlorophyllide. This reaction is catalyzed by a photoenzyme, protochlorophyllide oxidoreductase (POR) and consists in the attachment of two hydrogen atoms in positions C17 and C18 of the tetrapyrrole molecule of protochlorophyllide;the double bond is replaced with the single bond. Two hydrogen donors involved in protochloro-phyllide photoreduction are NADPH [1,2] and a conserved tyrosine residue Tyr193 of the photoenzyme POR [3]. The structure of active pigment-enzyme complex (Pchlide-POR-NADPH) ensures a favorable steric conditions for the transfer of hydride ion and proton. This review does not examine the ternary complex structure, but concentrates upon the mechanisms of primary photophysical and photochemical reactions during formation of chlorophyllide from protochlorophyllide in living objects (etiolated leaves and leaf homogenates) and model systems.

Fast mapping of a chlorophyll b synthesis-deficiency gene in barley(Hordeum vulgare L.) via bulked-segregant analysis with reduced-representation sequencing

Bulked-segregant analysis coupled with next-generation sequencing(BSA-seq) has emerged as an efficient tool for genetic mapping of single genes or major quantitative trait loci controlling(agronomic) traits of interest. However, such a mapping-by-sequencing approach usually relies on deep sequencing and advanced statistical methods. Application of BSA-Seq based on construction of reduced-representation libraries and allele frequency analysis permitted anchoring the barley pale-green(pg) gene on chromosome 3 HL. With further marker-assisted validation, pg was mapped to a 3.9 Mb physical-map interval. In the pg mutant a complete deletion of chlorophyllide a oxygenase(HvCAO) gene was identified.Because the product of this gene converts Chl a to Chl b, the pg mutant is deficient in Chl b.An independent Chl b-less mutant line M4437_2 carried a nonsynonymous substitution(F263 L) in the C domain of HvCAO. The study demonstrates an optimized pooling strategy for fast mapping of agronomically important genes using a segregating population.

Expression analysis of chlorophyllid a binding protein a secretory, red fluorescence protein in the midgut of silkworm, Bombyx mori

Chlorophyllid a binding protein （ chbp） was recently characterized by its ability to bind the prosthetic group of chlorophylls and little information is known regarding its expression. In the present study, we found that chpb was expressed highly and exclusively in the midgut of silkworm, Bombyx mori. The expression level of chbp was very high in the newly molted fifth instar larvae followed by gradual decline in the same instar. Our results demonstrated that CHBP was a secretory protein and located mainly in the apical of midgut epithelial cells. Real-time polymerase chain reaction analysis results showed that chpb highly expressed in the anterior midgut, threefold and sixfold higher compared with that of the middle midgut and posterior midgut, respectively, and chpb expression declined in darkness. In addition, the expression of chbp was affected by high-dose virus or bacterium infection.