Hirner B, Fischer W N, Rentsch D, Kwart M, Frommer W B
Insitut für Botanik, Universität Tübingen, Germany.
Plant J. 1998 Jun;14(5):535-44. doi: 10.1046/j.1365-313x.1998.00151.x.
Long distance transport of amino acids is mediated by several families of differentially expressed amino acid transporters. The two genes AAP1 and AAP2 encode broad specificity H(+)-amino acid co-transporters and are expressed to high levels in siliques of Arabidopsis, indicating a potential role in supplying the seeds with organic nitrogen. The expression of both genes is developmentally controlled and is strongly induced in siliques at heart stage of embryogenesis, shortly before induction of storage protein genes. Histochemical analysis of transgenic plants expressing promoter-GUS fusions shows that the genes have nonoverlapping expression patterns in siliques. AAP1 is expressed in the endosperm and the cotyledons whereas AAP2 is expressed in the vascular strands of siliques and in funiculi. The endosperm expression of AAP1 during early stages of seed development indicates that the endosperm serves as a transient storage tissue for organic nitrogen. Amino acids are transported in both xylem and phloem but during seed filling are imported only via the phloem. AAP2, which is expressed in the phloem of stems and in the veins supplying seeds, may function in uptake of amino acids assimilated in the green silique tissue, in the retrieval of amino acids leaking passively out of the phloem and in xylem-to-phloem transfer along the path. The promoters provide excellent tools to study developmental, hormonal and metabolic control of nitrogen nutrition during development and may help to manipulate the timing and composition of amino acid import into seeds.
氨基酸的长距离运输由几个差异表达的氨基酸转运蛋白家族介导。AAP1和AAP2这两个基因编码广泛特异性的H(+)-氨基酸共转运蛋白，在拟南芥的角果中高水平表达，表明其在为种子提供有机氮方面具有潜在作用。这两个基因的表达受发育调控，在胚胎发生心形期的角果中强烈诱导表达，就在贮藏蛋白基因诱导表达前不久。对表达启动子-GUS融合体的转基因植物进行组织化学分析表明，这两个基因在角果中的表达模式不重叠。AAP1在胚乳和子叶中表达，而AAP2在角果的维管束和珠柄中表达。种子发育早期AAP1在胚乳中的表达表明，胚乳作为有机氮的临时贮藏组织。氨基酸在木质部和韧皮部中都有运输，但在种子充实期间仅通过韧皮部导入。AAP2在茎的韧皮部和供应种子的叶脉中表达，可能在吸收绿色角果组织中同化的氨基酸、回收被动从韧皮部泄漏的氨基酸以及沿路径从木质部到韧皮部的转运中发挥作用。这些启动子为研究发育过程中氮营养的发育、激素和代谢调控提供了极好的工具，可能有助于控制氨基酸导入种子的时间和组成。
