Maggio Albino, Miyazaki Saori, Veronese Paola, Fujita Tomomichi, Ibeas José I, Damsz Barbara, Narasimhan Meena L, Hasegawa Paul M, Joly Robert J, Bressan Ray A
Center for Plant Environmental Stress Physiology, Purdue University, 1165 Horticulture Bldg, West Lafayette, Indiana 47907-1165, USA.
Plant J. 2002 Sep;31(6):699-712. doi: 10.1046/j.1365-313x.2002.01389.x.
An interesting observation, reported for transgenic plants that have been engineered to overproduce osmolytes, is that they often exhibit impaired growth in the absence of stress. As growth reduction and accumulation of osmolytes both typically result from adaptation, we hypothesized that growth reduction may actually result from osmolyte accumulation. To examine this possibility more closely, intracellular proline level was manipulated by expressing mutated derivatives of tomPRO2 (a Delta(1)-pyrroline-5-carboxylate synthetase, P5CS, from tomato) in Saccharomyces cerevisiae. This was done in the presence and absence of a functional proline oxidase, followed by selection and screening for increased accumulation of proline in the absence of any stress. Here we show, in support of our hypothesis, that the level of proline accumulation and the amount of growth are inversely correlated in cells grown under normal osmotic conditions. In addition, the intracellular concentration of proline also resulted in increases in ploidy level, vacuolation and altered accumulation of several different transcripts related to cell division and gene expression control. Because these cellular modifications are common responses to salt stress in both yeast and plants, we propose that proline and other osmolytes may act as a signaling/regulatory molecule able to activate multiple responses that are part of the adaptation process. As in previous studies with transgenic plants that overaccumulate osmolytes, we observed some increase in relative growth of proline-overaccumulating cells in mild hyperosmotic stress.
对于经过基因工程改造以过量产生渗透调节剂的转基因植物，有一个有趣的观察结果是，在没有胁迫的情况下它们通常生长受损。由于生长减少和渗透调节剂积累通常都是适应的结果，我们推测生长减少可能实际上是由渗透调节剂积累导致的。为了更仔细地研究这种可能性，通过在酿酒酵母中表达tomPRO2（一种来自番茄的Δ¹-吡咯啉-5-羧酸合成酶，P5CS）的突变衍生物来操纵细胞内脯氨酸水平。这是在有和没有功能性脯氨酸氧化酶的情况下进行的，随后在没有任何胁迫的情况下选择并筛选脯氨酸积累增加的情况。在这里，为支持我们的假设，我们表明在正常渗透条件下生长的细胞中，脯氨酸积累水平与生长量呈负相关。此外，脯氨酸的细胞内浓度还导致倍性水平增加、液泡化以及与细胞分裂和基因表达控制相关的几种不同转录本的积累改变。由于这些细胞修饰是酵母和植物对盐胁迫的常见反应，我们提出脯氨酸和其他渗透调节剂可能作为一种信号/调节分子，能够激活作为适应过程一部分的多种反应。与之前对过量积累渗透调节剂的转基因植物的研究一样，我们观察到在轻度高渗胁迫下脯氨酸过量积累细胞的相对生长有一些增加。
