Magnesium-protoporphyrin IX monomethyl ester cyclase (MPEC) catalyzes the conversion of MPME to divinyl protochlorophyllide (DVpchlide). This is an essential enzyme during chlorophyll (Chl) biosynthesis but details of its function in rice are still lacking. In a recent study, researchers identified a novel rice mutant yellow-leaf 1 (yl-1), which showed decreased Chl accumulation, abnormal chloroplast ultrastructure and attenuated photosynthetic activity.

Map-based cloning and over-expression analysis suggested that YL-1 encodes a subunit of MPEC. The YL-1 protein localizes in chloroplasts, and is mainly expressed in green tissues, with greatest abundance in leaves and young panicles. Results of qRT-PCR showed that Chl biosynthesis upstream genes were highly expressed in the yl-1 mutant, while downstream genes were compromised, indicatingYL-1 plays a pivotal role in the Chl biosynthesis. Furthermore, expression levels of photosynthesis and chloroplast development genes were also affected. RNA-seq results further proved that numerous membrane-associated genes, including many plastid membrane-associated genes, have altered expression pattern in the yl-1 mutant, implying YL-1 is required for plastid membrane stability.

This study confirms a putative MPME cyclase as a novel key enzyme essential for Chl biosynthesis and chloroplast membrane stability in rice.

 

Reference
Sheng Z, Lv Y, Li W, Luo R, Wei X, Xie L, et al. (2017) Yellow-Leaf 1 encodes a magnesium-protoporphyrin IX monomethyl ester cyclase, involved in chlorophyll biosynthesis in rice (Oryza sativa L.) PLoS ONE 12(5): e0177989 [article]

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