Manen J F, Simon P, Van Slooten J C, Osterås M, Frutiger S, Hughes G J
Jardin Botanique, Genève, Switzerland.
Plant Cell. 1991 Mar;3(3):259-70. doi: 10.1105/tpc.3.3.259.
Nodule senescence is one aspect of nitrogen fixation that is important to study from the perspective of improving the host-bacteroid interaction. In winged bean nodules, a 21-kilodalton protein is specifically expressed when senescence begins. Using subcellular fractionation, we observed that this plant protein interacts with the bacteroids. Microsequencing of the protein allowed us to obtain a specific oligonucleotide that was used to isolate the corresponding nodule cDNA. Sequence analysis of this cDNA revealed that the 21-kilodalton protein has all of the features of a legume Kunitz protease inhibitor. Subsequent analysis confirmed that this nodulin is indeed a protease inhibitor. Immunocytochemical study showed that the protease inhibitor is exclusively localized in infected senescent cells of the nodule, particularly in disorganized bacteroids, the peribacteroid membrane, vacuole membranes, and in the vacuole fluid. The specific expression of a protease inhibitor at senescence may be of particular interest if the targeted proteolytic activity is important for the symbiotic relationship. This point is discussed in relation to the known nodule proteases.
根瘤衰老作为固氮作用的一个方面，从改善宿主-类菌体相互作用的角度来看是一个重要的研究方向。在四棱豆根瘤中，一种21千道尔顿的蛋白质在衰老开始时特异性表达。通过亚细胞分级分离，我们观察到这种植物蛋白与类菌体相互作用。对该蛋白进行微量测序，使我们获得了一段特定的寡核苷酸，用于分离相应的根瘤cDNA。对该cDNA的序列分析表明，这种21千道尔顿的蛋白质具有豆科植物库尼茨蛋白酶抑制剂的所有特征。后续分析证实，这种根瘤蛋白确实是一种蛋白酶抑制剂。免疫细胞化学研究表明，该蛋白酶抑制剂仅定位在根瘤受感染的衰老细胞中，特别是在解体的类菌体、类菌体周膜、液泡膜以及液泡液中。如果靶向蛋白水解活性对共生关系很重要，那么蛋白酶抑制剂在衰老时的特异性表达可能会特别引人关注。本文结合已知的根瘤蛋白酶对这一点进行了讨论。
