Molecular Characterization of LjSWEET3, a Sugar Transporter in Nodules of Lotus japonicus
Molecular Characterization of LjSWEET3, a Sugar Transporter in Nodules of Lotus japonicus
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DOI：
10.1093/pcp/pcw190
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发表时间：
2016-12
影响因子：
4.9
通讯作者：
A. Sugiyama;Yuka Saida;M. Yoshimizu;Kojiro Takanashi;Davide Sosso;W. Frommer;K. Yazaki
中科院分区：
文献类型：
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作者：
A. Sugiyama;Yuka Saida;M. Yoshimizu;Kojiro Takanashi;Davide Sosso;W. Frommer;K. Yazaki
豆科植物共生固氮对全球氮循环有重要贡献。在根瘤中，常驻根瘤菌向宿主植物提供从大气N2中固定的氮营养物;反过来，植物向拟杆菌提供光合代谢产物作为碳源。在这一过程中，不同的转运蛋白参与不同的膜系统;然而，很少有人知道在分子水平上的碳流从宿主细胞的共生细菌。我们对百脉根根瘤中转运蛋白的功能进行了研究，发现百脉根根瘤中的13个SWEET基因中，SWEET基因组LjSWEET 3是SWEET转运蛋白家族的成员，在结节中高度表达。SWEET家族首先在拟南芥中被鉴定，其中该家族的成员参与韧皮部装载、花蜜分泌、花粉营养和种子填充。LjSWEET 3的表达在根瘤发育过程中强烈增加，并在成熟根瘤中达到最高水平。组织化学分析采用L.用LjSWEET 3启动子：GUS（β-葡萄糖醛酸酶）转化的拟南芥植株在根瘤的维管系统中显示出强表达。对在班氏烟草和日本黄连中表达的LjSWEET 3-绿色荧光蛋白（GFP）融合体的分析表明，LjSWEET 3定位于质膜。总之，这些数据与LjSWEET 3在糖向结核转运中的作用一致，并且还表明可能存在向结核供应碳的多种途径。
Symbiotic nitrogen fixation in legumes contributes greatly to the global nitrogen cycle on the earth. In nodules, resident rhizobia supply nitrogen nutrient fixed from atmospheric N2 to the host plant; in turn, the plant provides photosynthetic metabolites to bacteroids as a carbon source. In this process, various transporters are involved at different membrane systems; however, little is known at the molecular level about the flow of carbon from the host cells to the symbiotic bacteria. We have been studying transporters functioning in nodules of Lotus japonicus, and found that out of 13 SWEET genes in the L. japonicus genome LjSWEET3, a member of the SWEET transporter family, is highly expressed in nodules. The SWEET family was first identified in Arabidopsis, where members of the family are involved in phloem loading, nectar secretion, pollen nutrition and seed filling. The expression of LjSWEET3 strongly increased during nodule development and reached the highest level in mature nodules. Histochemical analysis using L. japonicus plants transformed with LjSWEET3 promoter:GUS (β-glucuronidase) showed strong expression in the vascular systems of nodules. Analysis of an LjSWEET3-green fluorescent protein (GFP) fusion expressed in Nicotiana banthamiana and Coptis japonica indicates that LjSWEET3 localizes to the plasma membrane. Together these data are consistent with a role for LjSWEET3 in sugar translocation towards nodules and also suggest the possible existence of multiple routes of carbon supply into nodules.