Hu Xueyun, Page Mike T, Sumida Akihiro, Tanaka Ayumi, Terry Matthew J, Tanaka Ryouichi
Institute of Low Temperature Science, Hokkaido University, Sapporo, 060-0819, Japan.
School of Life Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, China.
Plant J. 2017 Mar;89(6):1184-1194. doi: 10.1111/tpj.13455. Epub 2017 Feb 8.
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.
含有铁硫（Fe-S）簇的蛋白质在光合作用和氧化还原代谢等各种代谢过程中发挥着关键作用。在植物中参与Fe-S簇生物合成的蛋白质中，SUFBCD复合物的SUFB亚基似乎很独特，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，我们分析了两个SUFB突变体laf6和hmc1以及SUFB表达降低的RNA干扰（RNAi）株系的表型。在光照下生长时，laf6和hmc1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-原卟啉MME），这与Mg-原卟啉MME环化酶活性受损一致。SUFC和SUFD缺陷的RNAi株系都积累了相同的中间体，表明抑制Fe-S簇合成是这种损伤的主要原因。黑暗中生长的laf6幼苗的原卟啉IX（原卟啉IX）、Mg-原卟啉、Mg-原卟啉MME和3,8-二乙烯基原叶绿素ide a（DV-Pchlide）水平也有所增加，但在hmc1或SUFB RNAi株系中未观察到这种情况，SUFB过表达也不能使其恢复。此外，laf6突变体在远红光下长下胚轴的表型不能通过SUFB过表达得到挽救，并且与浅绿色的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簇的生物合成对叶绿素生物合成很重要，但laf6的表型不是由于SUFB突变。
