An Arabidopsis porB porC double mutant lacking light‐dependent NADPH:protochlorophyllide oxidoreductases B and C is highly chlorophyll‐deficient and developmentally arrested

Abstract

The first and second authors contributed equally to this work. SummaryA key reaction in the biosynthesis of chlorophylls (Chls) a and b from cyanobacteria through higher plants is the strictly light-dependent reduction of protochlorophyllide (Pchlide) a to chlorophyllide (Chlide) a. Angiosperms, unlike other photosynthetic organisms, rely exclusively upon this mechanism to reduce Pchlide and hence require light to green. In Arabidopsis, light-dependent Pchlide reduction is mediated by three structurally related but differentially regulated NADPH:Pchlide oxidoreductases, denoted as PORA, PORB, and PORC. The PORA and PORB genes, but not PORC, are strongly expressed early in seedling development. In contrast, expression of PORB and PORC, but not PORA, is observed in older seedlings and adult plants. We have tested the hypothesis that PORB and PORC govern light-dependent Chl biosynthesis throughout most of the plant development by identifying porB and porC mutants of Arabidopsis, the first higher plant por mutants characterized. The porB-1 and porC-1 mutants lack the respective POR transcripts and specific POR isoforms because of the interruption of the corresponding genes by a derivative of the maize Dissociation (Ds) transposable element. Single por mutants, grown photoperiodically, display no obvious phenotypes at the whole plant or chloroplast ultrastructural levels, although the porB-1 mutant has less extensive etioplast inner membranes. However, a light-grown porB-1 porC-1 double mutant develops a seedling-lethal xantha phenotype at the cotyledon stage, contains only small amounts of Chl a, and possesses chloroplasts with mostly unstacked thylakoid membranes. PORB and PORC thus seem to play redundant roles in maintaining light-dependent Chl biosynthesis in green plants, and are together essential for growth and development.

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“…Our results showed that chlorophyll contents were low in pop2-3 mutant than wild-type plant after 30 days in normal growth condition. Probably low chlorophyll content in mutant showed precocious leaf senescence [ Figure 1a], which was similar to the reported data in egy1 mutants, [27] porB1porC-1 double mutant of older seedlings, [30] and mex1 leaves of A. thaliana. [31] The chlorophyll content of GABA-T complement plant was approximately similar to wild-type plant up to 30 days [ Figure 1a].…”

Singlet oxygen- and EXECUTER1-mediated signaling is initiated in grana margins and depends on the protease FtsH2

“…2). Protein analysis of the EX1-GFP immunoprecipitate by mass spectrometry and Western blots revealed that EX1 forms part of a larger physical unit in grana margins that, in addition to the RC of PSII and several PSII light-harvesting Chl a/b proteins, comprises also chloroplast-specific subunits of the FtsH protease, the NADPHprotochlorophyllide oxidoreductases (POR) B and C catalyzing the light-dependent reduction of Pchlide to Chlide (21,22), the Tic110 protein translocation channel, the Ca 2+ -sensing protein and the GTP-binding Tu, and RAB GTPase homolog E1B elongation factors (Table S1 and Fig. S2).…”

Reactive oxygen species generation and signaling in plants

“…Transgenic seedlings grown under far red light when transferred to white light are more resistant to photobleaching because of high POR proteins. 75 The isolation and studies on Arabidopsis flu mutant by Klaus Apel's group confirm the role of Pchlide in 76 In the flu mutant there is no regulatory point at the GluTR level and there is a massive accumulation of Pchlide. Lee et al 77 have revealed that the TIGRINA d gene of barley is an ortholog of the FLU gene of Arabidopsis thaliana.…”