Delhaize E, Hebb D M, Ryan P R
Commonwealth Scientific and Industrial Research Organization Plant Industry, G.P.O. Box 1600, Canberra Australian Capital Territory 2601, Australia.
Plant Physiol. 2001 Apr;125(4):2059-67. doi: 10.1104/pp.125.4.2059.
Aluminum (Al) toxicity and poor phosphorus (P) availability are factors that limit plant growth on many agricultural soils. Previous work reported that expression of a Pseudomonas aeruginosa citrate synthase gene in tobacco (Nicotiana tabacum; CSb lines) resulted in improved Al tolerance (J.M. de la Fuente, V. Ramírez-Rodríguez, J.L. Cabrera-Ponce, L. Herrera-Estrella [1997] Science 276: 1566-1568) and an enhanced ability to acquire P from alkaline soils (J. López-Bucio, O. Martínez de la Vega, A. Guevara-García, L. Herrera-Estrella [2000] Nat Biotechnol 18: 450-453). These effects were attributed to the P. aeruginosa citrate synthase increasing the biosynthesis and efflux of citrate from roots. To verify these findings we: (a) characterized citrate efflux from roots of wild-type tobacco; (b) generated tobacco lines expressing the citrate synthase gene from P. aeruginosa; and (c) analyzed selected CSb lines described above. Al stimulated citrate efflux from intact roots of wild-type tobacco and root apices were found to be responsible for most of the efflux. Despite generating transgenic tobacco lines that expressed the citrate synthase protein at up to a 100-fold greater level than the previously described CSb lines, these lines did not show increased accumulation of citrate in roots or increased Al-activated efflux of citrate from roots. Selected CSb lines, similarly, failed to show differences compared with controls in either citrate accumulation or efflux. We conclude that expression of the P. aeruginosa citrate synthase gene in plants is unlikely to be a robust and easily reproducible strategy for enhancing the Al tolerance and P-nutrition of crop and pasture species.
铝（Al）毒性和磷（P）有效性差是限制许多农业土壤上植物生长的因素。先前的研究报道，在烟草（Nicotiana tabacum；CSb系）中表达铜绿假单胞菌柠檬酸合酶基因可提高对铝的耐受性（J.M. 德拉富恩特、V. 拉米雷斯 - 罗德里格斯、J.L. 卡布雷拉 - 庞塞、L. 埃雷拉 - 埃斯特雷亚 [1997] 《科学》276: 1566 - 1568），并增强从碱性土壤中获取磷的能力（J. 洛佩斯 - 布西奥、O. 马丁内斯·德拉维加、A. 格瓦拉 - 加西亚、L. 埃雷拉 - 埃斯特雷亚 [2000] 《自然生物技术》18: 450 - 453）。这些效应归因于铜绿假单胞菌柠檬酸合酶增加了根中柠檬酸的生物合成和外排。为了验证这些发现，我们：（a）对野生型烟草根中的柠檬酸外排进行了表征；（b）培育了表达铜绿假单胞菌柠檬酸合酶基因的烟草品系；（c）分析了上述选定的CSb系。铝刺激野生型烟草完整根中的柠檬酸外排，并且发现根尖是大部分外排的原因。尽管培育出了转基因烟草品系，其柠檬酸合酶蛋白的表达水平比先前描述的CSb系高100倍，但这些品系在根中柠檬酸的积累或铝激活的根中柠檬酸外排方面并未表现出增加。同样，选定的CSb系在柠檬酸积累或外排方面与对照相比也未显示出差异。我们得出结论，在植物中表达铜绿假单胞菌柠檬酸合酶基因不太可能是增强作物和牧草物种对铝的耐受性和磷营养的一种可靠且易于重复的策略。
