Department of Cell and System Biology, University of Toronto, 25 Willcocks Street, Toronto, M5S 3B2, ON, Canada.
Plant J. 2010 Sep;63(6):960-73. doi: 10.1111/j.1365-313X.2010.04291.x.
The formation of Arabidopsis leaf veins is believed to require canalization of auxin into discrete and continuous cell files to generate a highly reproducible branched and reticulate pattern. During canalization, incipient veins become preferred routes for auxin transport through expression and asymmetric localization of the PINFORMED1 (PIN1) auxin efflux protein: PIN1 expression narrows from a group of cells to a single cell file, and localization of PIN1 protein becomes polarized to the cell membrane facing a previously formed vein. The shift in PIN1 localization is believed to require active vesicle cycling and be auxin-dependent, generating an autoregulatory loop. Previously, we have shown that fkd1 mutant leaves have an open vein pattern that lacks distal vein meeting. Here, we identify FKD1 as encoding a pleckstrin homology domain- and DUF828-containing protein. A fusion of the FKD1 promoter and the GUS reporter gene was expressed in vascular tissue throughout the plant, and its expression in incipient veins in leaves narrows in a manner similar to that of PIN1. FKD1 expression in roots and leaves can be altered by changes to auxin response and auxin transport. In the absence of FKD1, PIN1::GFP narrowing to incipient veins is delayed, and localization to the apical cell face is infrequent. The lack of apical PIN1 localization correlates with the failure of newly forming veins to connect distally with previously formed veins. Our data suggest that FKD1 influences PIN1 localization in an auxin-dependent manner, and we propose that it represents a key component of the auxin canalization pathway.
拟南芥叶脉的形成被认为需要生长素在离散和连续的细胞层中进行分流，以产生高度可重复的分支和网状模式。在分流过程中，初生叶脉通过 PINFORMED1（PIN1）生长素外排蛋白的表达和不对称定位成为生长素运输的首选途径：PIN1 表达从一组细胞缩小到单个细胞层，PIN1 蛋白的定位变得极化到细胞膜，面向先前形成的叶脉。PIN1 定位的转变被认为需要活跃的囊泡循环，并依赖生长素，从而产生一个自我调节的循环。之前，我们已经表明，fkd1 突变体叶片具有开放的叶脉模式，缺乏远端叶脉的交汇。在这里，我们鉴定 FKD1 编码一个具有pleckstrin 同源结构域和 DUF828 结构域的蛋白。FKD1 启动子和 GUS 报告基因的融合在整个植物的血管组织中表达，其在叶片初生叶脉中的表达以类似于 PIN1 的方式变窄。通过改变生长素反应和生长素运输，可以改变 FKD1 在根和叶中的表达。在没有 FKD1 的情况下，PIN1::GFP 向初生叶脉的变窄被延迟，并且很少定位到顶端细胞面。缺乏顶端 PIN1 定位与新形成的叶脉不能与先前形成的叶脉远端连接相关。我们的数据表明，FKD1 以生长素依赖的方式影响 PIN1 的定位，我们提出它代表了生长素分流途径的关键组成部分。
