An Iron-Activated Citrate Transporter, MtMATE67, Is Required for Symbiotic Nitrogen Fixation
An Iron-Activated Citrate Transporter, MtMATE67, Is Required for Symbiotic Nitrogen Fixation
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DOI：
10.1104/pp.17.01538
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发表时间：
2018-03-01
期刊：
影响因子：
7.4
通讯作者：
Udvardi, Michael K.
中科院分区：
文献类型：
--
作者：
Kryvoruchko, Igor S.;Routray, Pratyush;Udvardi, Michael K.
铁是豆科植物根瘤共生固氮所必需的微量营养素，是两种生物中细菌固氮酶、植物豆类血红蛋白、呼吸氧化酶和其他铁蛋白活性所必需的。铁在植物组织内和组织之间的溶解和运输受到有机螯合剂的促进，如烟胺和柠檬酸盐。我们已经鉴定了一种多药和有毒化合物挤压家族的根瘤特异性柠檬酸转运蛋白，MtMATE67。MtMATE67基因在根瘤发育早期诱导表达，主要在成熟根瘤侵袭区表达。MtMATE67蛋白定位于根瘤细胞的质膜和感染细胞中类杆菌周围的共生体膜上。在卵母细胞中，MtMATE67以铁激活的方式将柠檬酸转运出细胞。MtMATE67基因功能的丧失导致铁在根瘤细胞的质外体中积累，共生固氮和植物生长显著下降。综上所述，这些结果表明MtMATE67在响应铁信号的根瘤细胞柠檬酸外流中起主要作用。这种外流是确保Fe(III)在质外体中的溶解性和移动性以及吸收到根瘤细胞中所必需的。同样，MtMATE67介导的柠檬酸转运到共生体空间会增加Fe(III)对根瘤菌类杆菌的溶解度和有效性。
Iron (Fe) is an essential micronutrient for symbiotic nitrogen fixation in legume nodules, where it is required for the activity of bacterial nitrogenase, plant leghemoglobin, respiratory oxidases, and other Fe proteins in both organisms. Fe solubility and transport within and between plant tissues is facilitated by organic chelators, such as nicotianamine and citrate. We have characterized a nodule-specific citrate transporter of the multidrug and toxic compound extrusion family, MtMATE67 of Medicago truncatula. The MtMATE67 gene was induced early during nodule development and expressed primarily in the invasion zone of mature nodules. The MtMATE67 protein was localized to the plasma membrane of nodule cells and also the symbiosome membrane surrounding bacteroids in infected cells. In oocytes, MtMATE67 transported citrate out of cells in an Fe-activated manner. Loss of MtMATE67 gene function resulted in accumulation of Fe in the apoplasm of nodule cells and a substantial decrease in symbiotic nitrogen fixation and plant growth. Taken together, the results point to a primary role of MtMATE67 in citrate efflux from nodule cells in response to an Fe signal. This efflux is necessary to ensure Fe(III) solubility and mobility in the apoplasm and uptake into nodule cells. Likewise, MtMATE67-mediated citrate transport into the symbiosome space would increase the solubility and availability of Fe(III) for rhizobial bacteroids.