在拟南芥中，一个编码线粒体脯氨酸脱氢酶（一种参与脯氨酸代谢的酶）的核基因受脯氨酸上调，但受脱水下调。
A nuclear gene encoding mitochondrial proline dehydrogenase, an enzyme involved in proline metabolism, is upregulated by proline but downregulated by dehydration in Arabidopsis.
作者信息
Kiyosue T, Yoshiba Y, Yamaguchi-Shinozaki K, Shinozaki K
机构信息
Laboratory of Plant Molecular Biology, Institute of Physical and Chemical Research (RIKEN), Tsukuba Life Science Center, Ibaraki, Japan.
出版信息
Plant Cell. 1996 Aug;8(8):1323-35. doi: 10.1105/tpc.8.8.1323.
Proline is one of the most common compatible osmolytes in water-stressed plants. The accumulation of proline in dehydrated plants is caused both by the activation of proline biosynthesis and by the inactivation of proline degradation; a decrease in the level of accumulated proline in rehydrated plants is caused both by the inhibition of proline biosynthesis and by the activation of proline degradation. The proline biosynthetic pathway has been well characterized, but the degradation of proline is poorly understood. Sequence analysis of an Arabidopsis cDNA clone, ERD5 (for early responsive to dehydration stress), isolated from plants dehydrated for 1 hr, revealed that it encodes a protein with identity to products of the yeast PUT1 (for proline utilization) gene (23.6% over 364 amino acids) and the Drosophila sluggish-A gene (34.5% over 255 amino acids). Their gene products are precursors of proline oxidases (dehydrogenase) (EC 1.5.99.8), which are the first enzymes involved in the conversion of proline to glutamic acid. Proline oxidase is localized in mitochondria. RNA gel blot analysis demonstrated that transcripts of the ERD5 gene were undetectable when plants had been dehydrated for 10 hr, but large amounts of the transcript accumulated when plants subsequently were rehydrated. Elevated levels of the transcript were also found in plants that had been incubated in a medium that contained proline. Immunologically, we showed that the product of ERD5 is localized in the mitochondrial fraction and accumulates in response to proline in cultured cells. Fusion genes for ERD5 and PUT1 complemented a put1 mutant of yeast, allowing put1 to grow with proline as the source of nitrogen. These results suggest that ERD5 encodes a precursor of proline dehydrogenase (oxidase), which is regulated at the level of mRNA accumulation in both dehydrated and rehydrated plants.
脯氨酸是水分胁迫植物中最常见的相容性渗透剂之一。脱水植物中脯氨酸的积累是由脯氨酸生物合成的激活和脯氨酸降解的失活共同引起的；复水植物中积累的脯氨酸水平降低是由脯氨酸生物合成的抑制和脯氨酸降解的激活共同引起的。脯氨酸生物合成途径已得到充分表征，但脯氨酸的降解却了解甚少。从脱水1小时的植物中分离出的拟南芥cDNA克隆ERD5（对脱水胁迫早期响应）的序列分析表明，它编码一种与酵母PUT1（脯氨酸利用）基因产物具有同源性的蛋白质（在364个氨基酸上有23.6%的同源性）以及果蝇迟钝-A基因产物（在255个氨基酸上有34.5%的同源性）。它们的基因产物是脯氨酸氧化酶（脱氢酶）（EC 1.5.99.8）的前体，脯氨酸氧化酶是脯氨酸转化为谷氨酸过程中涉及的第一种酶。脯氨酸氧化酶定位于线粒体中。RNA凝胶印迹分析表明，当植物脱水10小时时，未检测到ERD5基因的转录本，但当植物随后复水时，大量转录本积累。在含有脯氨酸的培养基中培养的植物中也发现了转录本水平的升高。通过免疫分析，我们表明ERD5的产物定位于线粒体部分，并在培养细胞中响应脯氨酸而积累。ERD5和PUT1的融合基因补充了酵母的put1突变体，使put1能够以脯氨酸作为氮源生长。这些结果表明，ERD5编码脯氨酸脱氢酶（氧化酶）的前体，其在脱水和复水植物中均在mRNA积累水平上受到调控。
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