Zhao Ting, Ling Hong-Qing
The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences. Datun Road, Chaoyang District, Beijing 100101, China.
Plant Cell Environ. 2007 Apr;30(4):518-27. doi: 10.1111/j.1365-3040.2007.01638.x.
In this work, we investigated the effects of pH and nitrogen forms on iron homeostasis and the expression profiles of genes involved in iron uptake and metabolism using tomato cultivar T3238 and its iron-inefficient mutant T3238fer. We showed that high external pH led to increased expression of four iron uptake genes (LeIRT1, LeIRT2, LeFRO1, LeNRAMP1) regardless of the nitrogen sources. Interestingly, the transcript level of FER was decreased at high pH and increased at low pH. In iron-inefficient mutant T3238fer, the expression of LeFRO1, LeIRT1 and LeNRAMP1 was much less than wild type under the culture conditions with high pH and on the non-buffered agar medium with NO(3) (-) as the sole N source, demonstrating that FER protein is required for the increased expression of LeFRO1, LeIRT1 and LeNRAMP1 under culture conditions with high pH. Considering the paradoxical expression patterns of FER to LeFRO1, LeIRT1 and LeNRAMP1 in T3238, we speculate that FER is essential, but is not the limited factor for the transcriptional regulation of the three iron uptake genes. In conclusion, the alteration of rhizosphere pH by assimilating NO(3) (-) or NH(4) (+) influenced Fe availability and consequently affected iron homeostasis in tomato. The enhanced expression of LeFRO1, LeIRT1 and LeNRAMP1 under the culture condition with high pH or on agar media with NO(3) (-) as the sole N source might be a consequence of reduced iron availability in the solution or agar medium at high pH.
在本研究中，我们利用番茄品种T3238及其铁低效突变体T3238fer，研究了pH值和氮形态对铁稳态以及铁吸收和代谢相关基因表达谱的影响。我们发现，无论氮源如何，高外部pH值都会导致四个铁吸收基因（LeIRT1、LeIRT2、LeFRO1、LeNRAMP1）的表达增加。有趣的是，FER的转录水平在高pH值时降低，在低pH值时升高。在铁低效突变体T3238fer中，在高pH值培养条件下以及以NO(3) (-)作为唯一氮源的非缓冲琼脂培养基上，LeFRO1、LeIRT1和LeNRAMP1的表达远低于野生型，这表明在高pH值培养条件下，FER蛋白是LeFRO1、LeIRT1和LeNRAMP1表达增加所必需的。考虑到T3238中FER与LeFRO1、LeIRT1和LeNRAMP1的矛盾表达模式，我们推测FER是必不可少的，但不是这三个铁吸收基因转录调控的限制因素。总之，通过同化NO(3) (-)或NH(4) (+)改变根际pH值会影响铁的有效性，进而影响番茄的铁稳态。在高pH值培养条件下或在以NO(3) (-)作为唯一氮源的琼脂培养基上，LeFRO1、LeIRT1和LeNRAMP1表达增强可能是高pH值下溶液或琼脂培养基中铁有效性降低的结果。
