The Combined Loss of Triose Phosphate and Xylulose 5-Phosphate/Phosphate Translocators Leads to Severe Growth Retardation and Impaired Photosynthesis in Arabidopsis thaliana tpt/xpt Double Mutants.
The Combined Loss of Triose Phosphate and Xylulose 5-Phosphate/Phosphate Translocators Leads to Severe Growth Retardation and Impaired Photosynthesis in Arabidopsis thaliana tpt/xpt Double Mutants.
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DOI：
10.3389/fpls.2018.01331
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发表时间：
2018
影响因子：
5.6
通讯作者：
Häusler RE
中科院分区：
文献类型：
--
作者：
Hilgers EJA;Schöttler MA;Mettler-Altmann T;Krueger S;Dörmann P;Eicks M;Flügge UI;Häusler RE
木酮糖5-磷酸/磷酸转运蛋白（XPT）代表了位于质体内被膜的磷酸转运蛋白（PT）家族的第四个功能成员。与其他三个成员相比，对XPT的生理作用知之甚少。基于其主要的运输底物（即，戊糖磷酸）XPT被认为是氧化戊糖磷酸途径（OPPP）的质体和质外分支之间的联系。由于XPT也能够运输磷酸丙糖，因此它也可以支持磷酸丙糖PT（TPT）在光下从叶绿体输出光合同化物（“碳的日间路径”），从而为整个植物提供碳水化合物。XPT的两个独立的敲除突变等位基因（xpt-1和xpt-2）缺乏任何特定的表型，表明XPT功能是多余的。然而，双突变体产生的交叉XPT-1的TPT（TPT-1和TPT-2）的不同突变等位基因的严重阻碍的大小，表现出高叶绿素荧光表型，和受损的光合电子传递速率。在双突变体中，从叶绿体输出磷酸丙糖被完全阻断。因此，蔗糖生物合成的前体完全来自淀粉周转（“碳的夜间路径”），这伴随着作为淀粉分解产物的麦芽糖的显著积累。此外，由OPPP的质体外分支产生的戊糖磷酸也在双突变体中积累。因此，活性XPT确实从质体外空间回收过量的戊糖磷酸，并使其可用于质体。进一步的代谢分析显示，磷酸化中间体在很大程度上保持不受影响，而富马酸和甘氨酸含量减少的双突变体。C/N比的评估表明，C-和N-代谢的共同限制可能是双突变体生长迟缓的原因。蔗糖的喂养部分挽救了双突变体的生长和光合表型。类囊体蛋白的免疫印迹，光合作用复合物的光谱测定，叶绿素a荧光发射光谱在77开尔文只能部分解释在光合作用中观察到的双突变体的约束。数据进行了讨论，连同OPPP和中央碳代谢方面。
The xylulose 5-phosphate/phosphate translocator (XPT) represents the fourth functional member of the phosphate translocator (PT) family residing in the plastid inner envelope membrane. In contrast to the other three members, little is known on the physiological role of the XPT. Based on its major transport substrates (i.e., pentose phosphates) the XPT has been proposed to act as a link between the plastidial and extraplastidial branches of the oxidative pentose phosphate pathway (OPPP). As the XPT is also capable of transporting triose phosphates, it might as well support the triose phosphate PT (TPT) in exporting photoassimilates from the chloroplast in the light (‘day path of carbon’) and hence in supplying the whole plant with carbohydrates. Two independent knockout mutant alleles of the XPT (xpt-1 and xpt-2) lacked any specific phenotype, suggesting that the XPT function is redundant. However, double mutants generated from crossings of xpt-1 to different mutant alleles of the TPT (tpt-1 and tpt-2) were severely retarded in size, exhibited a high chlorophyll fluorescence phenotype, and impaired photosynthetic electron transport rates. In the double mutant the export of triose phosphates from the chloroplasts is completely blocked. Hence, precursors for sucrose biosynthesis derive entirely from starch turnover (‘night path of carbon’), which was accompanied by a marked accumulation of maltose as a starch breakdown product. Moreover, pentose phosphates produced by the extraplastidial branch of the OPPP also accumulated in the double mutants. Thus, an active XPT indeed retrieves excessive pentose phosphates from the extra-plastidial space and makes them available to the plastids. Further metabolic profiling revealed that phosphorylated intermediates remained largely unaffected, whereas fumarate and glycine contents were diminished in the double mutants. The assessment of C/N-ratios suggested co-limitations of C- and N-metabolism as possible cause for growth retardation of the double mutants. Feeding of sucrose partially rescued the growth and photosynthesis phenotypes of the double mutants. Immunoblots of thylakoid proteins, spectroscopic determinations of photosynthesis complexes, and chlorophyll a fluorescence emission spectra at 77 Kelvin could only partially explain constrains in photosynthesis observed in the double mutants. The data are discussed together with aspects of the OPPP and central carbon metabolism.
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影响因子：
7.4
作者：
Baxter, Charles J.;Redestig, Henning;Sweetlove, Lee J.
通讯作者：
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