Fernández-Pérez Francisco, Pomar Federico, Pedreño María A, Novo-Uzal Esther
Department of Plant Biology, University of Murcia, Murcia, 30100, Spain.
Department of Animal Biology, Plant Biology and Ecology, 15071, University of A Coruña, A Coruña, Spain.
Physiol Plant. 2015 Jul;154(3):395-406. doi: 10.1111/ppl.12310. Epub 2014 Dec 22.
Lignins result from the oxidative polymerization of three hydroxycinnamyl (p-coumaryl, coniferyl and sinapyl) alcohols in a reaction mediated by peroxidases (EC 1.11.1.7) and laccases (EC 1.10.3.2), yielding H, G and S units, respectively. Although both acidic and basic peroxidases can oxidize p-coumaryl and coniferyl alcohol, only basic peroxidases are able to oxidize sinapyl alcohol. The AtPrx52 from Arabidopsis is a basic peroxidase that has been reported to be highly homologous to the basic peroxidase of Zinnia elegans, the only peroxidase which has been unequivocally linked to lignin formation. Here, we show how the suppression of AtPrx52 causes a change in lignin composition, mainly at the level of stem interfascicular fibers. Quantification of lignins in two different atprx52 knock-out mutants revealed a decrease of lignin amount compared with wild type. The S/G ratio, obtained by both nitrobenzene oxidation and thioacidolysis, indicated a decrease in S units in the atprx52 mutants. As deduced from Wiesner and mainly Mäule staining, this reduction in S unit content appears to be restricted to the interfascicular fibers. Moreover, quantitative polymerase chain reaction analysis in atprx52 plants showed a general downregulation of genes involved in lignin biosynthetic pathway, as well as genes related to secondary cell wall. On the other hand, other routes from phenylpropanoid metabolism were induced. Taken together, our results indicate that AtPrx52 is involved in the synthesis of S units in interfascicular fibers at late stages of the lignification process.
木质素是由三种羟基肉桂醇（对香豆醇、松柏醇和芥子醇）在过氧化物酶（EC 1.11.1.7）和漆酶（EC 1.10.3.2）介导的反应中发生氧化聚合而产生的，分别生成H、G和S单元。虽然酸性和碱性过氧化物酶都能氧化对香豆醇和松柏醇，但只有碱性过氧化物酶能够氧化芥子醇。拟南芥中的AtPrx52是一种碱性过氧化物酶，据报道它与百日草的碱性过氧化物酶高度同源，百日草的碱性过氧化物酶是唯一一种已明确与木质素形成相关的过氧化物酶。在此，我们展示了AtPrx52的抑制如何导致木质素组成的变化，主要是在茎间纤维水平上。对两个不同的atprx52基因敲除突变体中的木质素进行定量分析，结果显示与野生型相比，木质素含量降低。通过硝基苯氧化和硫代酸解获得的S/G比值表明，atprx52突变体中S单元减少。从维斯纳染色和主要的迈尔染色推断，S单元含量的这种降低似乎仅限于间纤维。此外，对atprx52植株进行的定量聚合酶链反应分析表明，参与木质素生物合成途径的基因以及与次生细胞壁相关的基因普遍下调。另一方面，苯丙烷代谢的其他途径被诱导。综上所述，我们的结果表明AtPrx52在木质化过程后期参与了间纤维中S单元的合成。
