Vascular cambium-localized AtSPDT mediates xylem-to-phloem transfer of phosphorus for its preferential distribution in Arabidopsis

First author: Guangda Ding; Affiliations: Okayama University (冈山大学): Kurashiki, Japan

Corresponding author: Jian Feng Ma

Recent progress has shown that the preferential distribution of mineral nutrients is mediated by node-based transporters in gramineous plants, but it is poorly understood for the mechanisms of preferential distribution in dicots. Here, we report a distinct mechanism for the preferential distribution of phosphorus (P) through detailed functional analysis of AtSPDT/AtSULTR3;4 (SULTR-like P Distribution Transporter) in Arabidopsis. AtSPDT is a homolog of rice OsSPDT and localized to the plasma membrane. It also showed proton-dependent transport activity for P. AtSPDT was mainly expressed in rosette basal region and leaf petiole and its expression was up-regulated by P-deficiency. Tissue-specific analysis showed that AtSPDT was mainly located at the vascular cambium of different organs, as well as in the parenchyma tissues of both xylem and phloem region. Knockout of this gene inhibited the growth of new leaves under low P due to decreased P distribution to those organs. The seed yield was similar between mutant lines and wild type, but the mutant lines contained 8.2%-33.6% less P in seeds. These results indicate that AtSPDT localized at the vascular cambium is involved in the preferential distribution of P to the developing tissues through the xylem-to-phloem transfer mainly in rosette basal region and leaf petiole.

近来的一些研究显示禾本科植物中矿物质营养的优先分配是由基于节的转运体实现的，但在双子叶中有关矿物质营养的优先分布机制还不清楚。本文中，作者通过对拟南芥类SULTR磷分布运输蛋白AtSPDT/AtSULTR3;4的详细功能鉴定，发现了一个完全不同于之前所报道的磷优先分配机制。AtSPDT是水稻中OsSPDT的同源蛋白，定位于质膜上。AtSPDT显示出质子依赖性的磷转运活性。AtSPDT基因主要在莲座叶基部区域以及叶柄中表达，并且其会在磷缺乏条件下会上调表达。组织特异性分析显示AtSPDT蛋白主要定位于不同器官的维管形成层，同时还有木质部和韧皮部区域的薄壁组织。该基因的敲除突变体会在低磷条件下降低组织器官中的磷分布，从而抑制新叶的生长。突变体和野生型种子产量类似，但突变体种子的磷含量降低了8.2%-33.6%。本文的结果揭示了AtSPDT定位于莲座叶基部区域以及叶柄中的维管形成层，通过从木质部向韧皮部的运输参与了磷的优先分配，以保证新的组织的正常发育。

通讯：Jian Feng Ma (http://www.rib.okayama-u.ac.jp/plant.stress/english/member.html)

研究方向：植物的矿物质胁迫耐受性以及矿物质运输系统。

doi: https://doi.org/10.1016/j.molp.2019.10.002

Journal: Molecular Plants

Published date: October 10, 2019