Marjamaa Kaisa, Hildén Kristiina, Kukkola Eija, Lehtonen Mikko, Holkeri Heidi, Haapaniemi Pekka, Koutaniemi Sanna, Teeri Teemu H, Fagerstedt Kurt, Lundell Taina
Department of Biological and Environmental Sciences, University of Helsinki, P.O. Box 65, 00014 Helsinki, Finland.
Plant Mol Biol. 2006 Jul;61(4-5):719-32. doi: 10.1007/s11103-006-0043-6.
Plant class III peroxidases (POXs) take part in the formation of lignin and maturation of plant cell walls. However, only a few examples of such peroxidases from gymnosperm tree species with highly lignified xylem tracheids have been implicated so far. We report here cDNA cloning of three xylem-expressed class III peroxidase encoding genes from Norway spruce (Picea abies). The translated proteins, PX1, PX2 and PX3, contain the conserved amino acids required for heme-binding and peroxidase catalysis. They all begin with putative secretion signal propeptide sequences but diverge substantially at phylogenetic level, grouping to two subclusters when aligned with other class III plant peroxidases. In situ hybridization analysis on expression of the three POXs in Norway spruce seedlings showed that mRNA coding for PX1 and PX2 accumulated in the cytoplasm of young, developing tracheids within the current growth ring where lignification is occurring. Function of the putative N-terminal secretion signal peptides for PX1, PX2 and PX3 was confirmed by constructing chimeric fusions with EGFP (enhanced green fluorescent protein) and expressing them in tobacco protoplasts. Full-length coding region of px1 was also heterologously expressed in Catharanthus roseus hairy root cultures. Thus, at least the spruce PX1 peroxidase is processed via the endoplasmic reticulum (ER) most likely for secretion to the cell wall. Thereby, PX1 displays correct spatiotemporal localization for participation in the maturation of the spruce tracheid secondary cell wall.
植物III类过氧化物酶（POXs）参与木质素的形成和植物细胞壁的成熟。然而，到目前为止，只有少数来自具有高度木质化木质部管胞的裸子植物树种的此类过氧化物酶的例子。我们在此报告从挪威云杉（Picea abies）中克隆出三个在木质部表达的III类过氧化物酶编码基因的cDNA。翻译后的蛋白质PX1、PX2和PX3含有血红素结合和过氧化物酶催化所需的保守氨基酸。它们都以假定的分泌信号前肽序列开头，但在系统发育水平上有很大差异，与其他III类植物过氧化物酶比对时分为两个亚群。对挪威云杉幼苗中三种POXs表达的原位杂交分析表明，编码PX1和PX2的mRNA在当前生长环内正在发生木质化的年轻发育中管胞的细胞质中积累。通过构建与增强绿色荧光蛋白（EGFP）的嵌合融合体并在烟草原生质体中表达，证实了PX1、PX2和PX3假定的N端分泌信号肽的功能。px1的全长编码区也在长春花毛状根培养物中进行了异源表达。因此，至少云杉PX1过氧化物酶很可能是通过内质网（ER）进行加工以便分泌到细胞壁。由此，PX1显示出正确的时空定位，以参与云杉管胞次生细胞壁的成熟。
