The iron-sulfur cluster biosynthesis protein SUFB is required for chlorophyll synthesis, but not phytochrome signaling.
The iron-sulfur cluster biosynthesis protein SUFB is required for chlorophyll synthesis, but not phytochrome signaling.
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DOI：
10.1111/tpj.13455
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发表时间：
2017-03
期刊：
影响因子：
--
通讯作者：
Tanaka R
中科院分区：
文献类型：
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作者：
Hu X;Page MT;Sumida A;Tanaka A;Terry MJ;Tanaka R
含有铁硫簇的蛋白质在光合作用和氧化还原代谢等多种代谢过程中起着关键作用。在植物中参与Fe-S簇生物合成的蛋白质中，SUFBCD复合物的SUFB亚基似乎是独特的，因为据报道SUFB参与叶绿素代谢和光敏色素介导的信号传导。为了深入了解SUFB蛋白的功能，我们分析了两种SUFB突变体laf 6和hmc 1的表型，以及SUFB表达降低的RNA干扰（RNAi）株系。当在光照下生长时，laf 6和hmc 1突变体以及SUFB RNAi株系积累了更高水平的叶绿素生物合成中间体Mg-原卟啉IX单甲酯（Mg-原MME），这与Mg-原MME环化酶活性受损一致。SUFC-和SUFD-缺陷RNAi系都积累了相同的中间体，这表明Fe-S簇合成的抑制是这种损伤的主要原因。黑暗生长的laf 6幼苗也显示出原卟啉IX（Proto IX）、Mg-原、Mg-原MME和3，8-二乙烯基原叶绿素a（DV-Pchlide）水平的增加，但这在hmc 1或SUFB RNAi系中没有观察到，也没有被SUFB过表达补充。此外，laf 6突变体的长下胚轴在远红光下的表型不能通过SUFB过表达来拯救，并且与淡绿色SUFB-缺陷表型分离，表明它不是由SUFB基因座的突变引起的。这些结果表明，Fe-S簇的生物合成对于叶绿素生物合成是重要的，但laf 6表型不是由于SUFB突变。我们证明了Fe-S生物合成是Mg-原卟啉单甲酯环化酶活性所必需的，这是叶绿素前体原叶绿酸合成中的一个重要步骤。然而，我们发现laf 6突变体的长下胚轴表型不是由于Fe-S生物合成蛋白SUFB的缺陷，而是第二个位点突变的结果。
Proteins that contain iron–sulfur (Fe–S) clusters play pivotal roles in various metabolic processes such as photosynthesis and redox metabolism. Among the proteins involved in the biosynthesis of Fe–S clusters in plants, the SUFB subunit of the SUFBCD complex appears to be unique because SUFB has been reported to be involved in chlorophyll metabolism and phytochrome‐mediated signaling. To gain insights into the function of the SUFB protein, we analyzed the phenotypes of two SUFB mutants, laf6 and hmc1, and RNA interference (RNAi) lines with reduced SUFB expression. When grown in the light, the laf6 and hmc1 mutants and the SUFB RNAi lines accumulated higher levels of the chlorophyll biosynthesis intermediate Mg‐protoporphyrin IX monomethylester (Mg‐proto MME), consistent with the impairment of Mg‐proto MME cyclase activity. Both SUFC‐ and SUFD‐deficient RNAi lines accumulated the same intermediate, suggesting that inhibition of Fe‐S cluster synthesis is the primary cause of this impairment. Dark‐grown laf6 seedlings also showed an increase in protoporphyrin IX (Proto IX), Mg‐proto, Mg‐proto MME and 3,8‐divinyl protochlorophyllide a (DV‐Pchlide) levels, but this was not observed in hmc1 or the SUFB RNAi lines, nor was it complemented by SUFB overexpression. In addition, the long hypocotyl in far‐red light phenotype of the laf6 mutant could not be rescued by SUFB overexpression and segregated from the pale‐green SUFB‐deficient phenotype, indicating it is not caused by mutation at the SUFB locus. These results demonstrate that biosynthesis of Fe–S clusters is important for chlorophyll biosynthesis, but that the laf6 phenotype is not due to a SUFB mutation. We demonstrate that Fe‐S biosynthesis is required for Mg‐protoporphyrin monomethylester cyclase activity, an essential step in the synthesis of the chlorophyll precursor protochlorophyllide. However, we show that the long hypocotyl phenotype reported for the laf6 mutant is not due to a deficiency in the Fe‐S biosynthesis protein SUFB, but instead is the result of a second site mutation.