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首页> 外文期刊>Journal of Experimental Botany >Evidence for sugar signalling in the regulation of asparagine synthetase gene expressed in Phaseolus vulgaris roots and nodules
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Evidence for sugar signalling in the regulation of asparagine synthetase gene expressed in Phaseolus vulgaris roots and nodules

机译：调控菜豆根和根瘤中天冬酰胺合成酶基因糖信号的证据

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摘要

A cDNA clone, designated as PvNAS2, encoding asparagine amidotransferase (asparagine synthetase) was isolated from nodule tissue of common bean (Phaseolus vulgaris cv. Negro Jamapa). Southern blot analysis indicated that asparagine synthetase in bean is encoded by a small gene family. Northern analysis of RNAs from various plant organs demonstrated that PvNAS2 is highly expressed in roots, followed by nodules in which it is mainly induced during the early days of nitrogen fixation. Investigations with the PvNAS2 promoter gusA fusion revealed that the expression of PvNAS2 in roots is confined to vascular bundles and meristematic tissues, while in root nodules its expression is solely localized to vascular traces and outer cortical cells encompassing the central nitrogen-fixing zone, but never detected in either infected or non-infected cells located in the central region of the nodule. PvNAS2 is down-regulated when carbon availability is reduced in nodules, and the addition of sugars to the plants, mainly glucose, boosted its induction, leading to the increased asparagine production. In contrast to PvNAS2 expression and the concomitant asparagine synthesis, glucose supplement resulted in the reduction of ureide content in nodules. Studies with glucose analogues as well as hexokinase inhibitors suggested a role for hexokinase in the sugar-sensing mechanism that regulates PvNAS2 expression in roots. In light of the above results, it is proposed that, in bean, low carbon availability in nodules prompts the down-regulation of the asparagine synthetase enzyme and concomitantly asparagine production. Thereby a favourable environment is created for the efficient transfer of the amido group of glutamine for the synthesis of purines, and then ureide generation.
机译：从普通豆（菜豆（Phaseolus vulgaris cv.Negro Jamapa））的根瘤组织中分离出一个编码为PvNAS2的cDNA克隆，其编码天冬酰胺酰胺转移酶（天冬酰胺合成酶）。 Southern印迹分析表明，豆中的天冬酰胺合成酶由一个小基因家族编码。对来自各种植物器官的RNA的Northern分析表明，PvNAS2在根中高表达，其次是小结节，主要在固氮初期被诱导。对PvNAS2启动子gusA融合的研究表明，PvNAS2在根中的表达仅限于维管束和分生组织，而在根瘤中，其表达仅局限于维管迹线和覆盖中央固氮区的外部皮层细胞，但从未在位于结节中心区域的受感染或未受感染的细胞中检测到。当结节中碳的利用率降低时，PvNAS2被下调，向植物中添加糖（主要是葡萄糖）可增强其诱导作用，从而导致天冬酰胺产量增加。与PvNAS2表达和随之而来的天冬酰胺合成相反，葡萄糖补充剂导致结节中的尿素含量降低。对葡萄糖类似物以及己糖激酶抑制剂的研究表明，己糖激酶在调节根中PvNAS2表达的糖敏机制中起作用。根据以上结果，提出在豆类中，结节中低碳可利用性促进了天冬酰胺合成酶的下调并伴随天冬酰胺的生产。从而创造了有利的环境，用于谷氨酰胺的酰胺基团的有效转移，以合成嘌呤，然后生成脲。

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