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IBBR publication #1227

Transformation of Lotus corniculatus plants with Escherichia coli asparagines synthetase A: effect on nitrogen assimilation and plant development

Bellucci M, Ederli L, De Marchis F, Pasqualini S, Arcioni S

Plant Cell, Tissue And Organ Culture 78: 139-150. [ISSN: 0167-6857] (2004)
doi: 10.1023/B:TICU.0000022554.27490.3d

Asparagine and glutamine are major forms of nitrogen in the phloem sap of many higher plants. In vascular plants, glutamine-dependent asparagines synthetase (AS) is the primary source of asparagine. In Escherichia coli, asparagines is synthesized by the action of two distinct enzymes, AS-A which utilizes ammonia as a nitrogen donor, and AS-B which utilizes both glutamine and ammonia as substrates, but with a preference for glutamine. In this study, the possibility to endow plants with ammonia-dependent AS activity was investigated by heterologous expression of E. coli asnA gene with the aim to introduce a new ammonium assimilation pathway in plants. The bacterial gene is placed under the control of light-dependent promoters, and introduced by transformation into Lotus corniculatus plants. Analysis of transgenic plants has revealed a phenomenon of transgene silencing which has prevented asnA expression in several transgenics. The asnA-expressing plants are characterized by premature flowering and reduced growth. A significant reduction of the total free amino acid accumulation in transgenic plants is observed. Surprisingly, the content of asparagine in wild-type plants is about 2.5-fold higher that that of transgenic plants. While glutamine levels in transgenic plants are about 3-4-fold higher than those in wild-type plants, aspartate levels are significantly lower. Transformation with asnA also induced a significant reduction of photosynthesis when measured under saturated light and ambient CO2 conditions

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