Mutation in Mg-Protoporphyrin IX Monomethyl Ester Cyclase Causes Yellow and Spotted Leaf Phenotype in Rice

Pecan is one of the most famous nut species in the world. The phenotype of mutants with albino leaves was found in the process of seeding pecan, providing ideal material for the study of the molecular mechanisms leading to the chlorina phenotype in plants. Both chlorophyll a and chlorophyll b contents in albino leaves (ALs) were significantly lower than those in green leaves (GLs). A total of 5171 differentially expression genes (DEGs) were identified in the comparison of ALs vs. GLs using high-throughput transcriptome sequencing; 2216 DEGs (42.85%) were upregulated and 2955 DEGs (57.15%) were downregulated. The expressions of genes related to chlorophyll biosynthesis (HEMA1, encoding glutamyl-tRNA reductase; ChlH, encoding Mg-protoporphyrin IX chelatase (Mg-chelatase) H subunit; CRD, encoding Mg-protoporphyrin IX monomethylester cyclase; POR, encoding protochlorophyllide reductase) in ALs were significantly lower than those in GLs. However, the expressions of genes related to chlorophyll degradation (PAO, encoding pheophorbide a oxygenase) in ALs were significantly higher than those in GLs, indicating that disturbance of chlorophyll a biosynthesis and intensification of chlorophyll degradation lead to the absence of chlorophyll in ALs of pecan. A total of 72 DEGs associated with photosynthesis pathway were identified in ALs compared to GLs, including photosystem I (15), photosystem II (19), cytochrome b6-f complex (3), photosynthetic electron transport (6), F-type ATPase (7), and photosynthesis-antenna proteins (22). Moreover, almost all the genes (68) mapped in the photosynthesis pathway showed decreased expression in ALs compared to GLs, declaring that the photosynthetic system embedded within the thylakoid membrane of chloroplast was disturbed in ALs of pecan. This study provides a theoretical basis for elucidating the molecular mechanism underlying the phenotype of chlorina seedlings of pecan.

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The Ycf54 protein is part of the membrane component of Mg-protoporphyrin IX monomethyl ester cyclase from barley (Hordeum vulgareL.)

FEBS Journal ◽

10.1111/febs.12790 ◽

2014 ◽

Vol 281 (10) ◽

pp. 2377-2386 ◽

Cited By ~ 19

Author(s):

David Bollivar ◽

Ilka Braumann ◽

Kasper Berendt ◽

Simon P. Gough ◽

Mats Hansson

Keyword(s):

Protoporphyrin Ix ◽

Membrane Component ◽

Monomethyl Ester

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Localization of Mg-Chelatase and Mg-Protoporphyrin IX Monomethyl Ester (Oxidative) Cyclase Activities within Isolated, Developing Cucumber Chloroplasts

PLANT PHYSIOLOGY ◽

10.1104/pp.75.3.662 ◽

1984 ◽

Vol 75 (3) ◽

pp. 662-664 ◽

Cited By ~ 43

Author(s):

Thomas P. Fuesler ◽

Yum-Shing Wong ◽

Paul A. Castelfranco

Keyword(s):

Protoporphyrin Ix ◽

Mg Chelatase ◽

Monomethyl Ester

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Further observations on the Mg-protoporphyrin IX monomethyl ester (oxidative) cyclase system

Biochemical Journal ◽

10.1042/bj2900355 ◽

1993 ◽

Vol 290 (2) ◽

pp. 355-359 ◽

Cited By ~ 17

Author(s):

B J Whyte ◽

P A Castelfranco

Keyword(s):

Pentose Phosphate Pathway ◽

Protoporphyrin Ix ◽

Companion Paper ◽

Pentose Phosphate ◽

Chloroplast Pigments ◽

Cyclization Process ◽

Reconstituted System ◽

Sugar Phosphates ◽

Cytochrome P 450 ◽

Monomethyl Ester

The Mg-protoporphyrin IX monomethyl ester (oxidative) cyclase was strongly inhibited by CN- and N3- in a reconstituted system, but was inhibited slightly or not at all by the same reagents in intact developing chloroplasts. Known inhibitors of cytochrome P-450 processes showed no consistent effect. Benzoquinone and quinol, which can give rise to the same semiquinone by one-electron redox events, were strong inhibitors of the cyclase. It was previously shown that O2 and a source of electrons are required in the cyclization process. The substrates for the dehydrogenases of the pentose phosphate pathway (glucose 6-phosphate and 6-phosphogluconate) were effective reductants in the reconstituted system with supernatant that had been dialysed or passed through Sephadex G-50, in the absence of added NADP+. However, inhibitor studies suggested that the electrons from these sugar phosphates reached the cyclase system via NADPH. Therefore we infer the presence of protein-bound NADP+ that can be reduced by glucose 6-phosphate and 6-phosphogluconate and donate reducing equivalents to the cyclase system. This bound NADPH pool may be particularly effective in the cyclization process, owing to channeling. These findings are discussed in relation to the results of a companion paper [Whyte and Castelfranco (1993) Biochem. J. 290, 361-367] on the breakdown of chloroplast pigments in the same reconstituted system.

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Chlorophyll a biosynthesis

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1976.0010 ◽

1976 ◽

Vol 273 (924) ◽

pp. 207-225 ◽

Cited By ~ 10

Keyword(s):

Chlorophyll A ◽

Chlorophyll Biosynthesis ◽

Protoporphyrin Ix ◽

Chlorophyll Synthesis ◽

Synthesis Reaction ◽

Etiolated Leaves ◽

Regulatory Aspects ◽

Vinyl Group ◽

Chlorophyll A Biosynthesis ◽

Monomethyl Ester

Protoporphyrin IX is believed to be an intermediate common to both haem and chlorophyll biosynthesis. The pathway specific to chlorophyll starts with magnesium protoporphyrin and its monomethyl ester. Two routes have been proposed for conversion of the latter compound to protochlorophyllide: A, formation of the isocyclic ring followed by reduction of the 4-vinyl group, or B, reduction of the 4-vinyl group followed by formation of the isocyclic ring. Membranes prepared from isolated barley etioplasts are found to convert magnesium 2,4-divinylphaeoporphyrin a 5 monomethyl ester to chlorophyllide a at a rate equal to that of chlorophyll synthesis in intact leaves: this result supports route A. NADPH is necessary to maintain the two successive reductive steps: reduction of the 4-vinyl group and then the photoreduction of ring IV to yield chlorophyllide. The prohaem content of etiolated leaves does not increase during the phase of active chlorophyll synthesis although evidence is presented that suggests that the ALA synthesis reaction that regulates chlorophyll synthesis is common to both pathways. This and other regulatory aspects are discussed.

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