Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706-1574, USA.
Plant Physiol. 2011 Aug;156(4):1878-93. doi: 10.1104/pp.111.179812. Epub 2011 Jun 8.
Plant root development is mediated by the concerted action of the auxin and cytokinin phytohormones, with cytokinin serving as an antagonist of auxin transport. Here, we identify the AUXIN UP-REGULATED F-BOX PROTEIN1 (AUF1) and its potential paralog AUF2 as important positive modifiers of root elongation that tether auxin movements to cytokinin signaling in Arabidopsis (Arabidopsis thaliana). The AUF1 mRNA level in roots is strongly up-regulated by auxin but not by other phytohormones. Whereas the auf1 single and auf1 auf2 double mutant roots grow normally without exogenous auxin and respond similarly to the wild type upon auxin application, their growth is hypersensitive to auxin transport inhibitors, with the mutant roots also having reduced basipetal and acropetal auxin transport. The effects of auf1 on auxin movements may be mediated in part by the misexpression of several PIN-FORMED (PIN) auxin efflux proteins, which for PIN2 reduces its abundance on the plasma membrane of root cells. auf1 roots are also hypersensitive to cytokinin and have increased expression of several components of cytokinin signaling. Kinematic analyses of root growth and localization of the cyclin B mitotic marker showed that AUF1 does not affect root cell division but promotes cytokinin-mediated cell expansion in the elongation/differentiation zone. Epistasis analyses implicate the cytokinin regulator ARR1 or its effector(s) as the target of the SKP1-Cullin1-F Box (SCF) ubiquitin ligases assembled with AUF1/2. Given the wide distribution of AUF1/2-type proteins among land plants, we propose that SCF(AUF1/2) provides additional cross talk between auxin and cytokinin, which modifies auxin distribution and ultimately root elongation.
植物根系的发育是由生长素和细胞分裂素这两种植物激素协同作用介导的，其中细胞分裂素作为生长素运输的拮抗剂。在这里，我们鉴定出生长素上调 F -box 蛋白 1（AUF1）及其潜在的旁系同源物 AUF2 是重要的正调节剂，它们将生长素的运动与拟南芥（Arabidopsis thaliana）中的细胞分裂素信号联系起来，从而促进根伸长。生长素强烈地上调根中 AUF1mRNA 的水平，但其他植物激素不能上调。虽然 auf1 单突变体和 auf1 auf2 双突变体的根在没有外源生长素的情况下正常生长，并且对生长素的应用反应与野生型相似，但它们的生长对生长素运输抑制剂高度敏感，突变体根的生长素向基和向顶运输也减少。auf1 对生长素运动的影响可能部分是通过几种 PIN 形成（PIN）生长素外排蛋白的错误表达介导的，这导致 PIN2 在根细胞的质膜上的丰度降低。auf1 根也对细胞分裂素敏感，并且细胞分裂素信号的几个成分的表达增加。根生长的运动学分析和细胞周期素 B 有丝分裂标记物的定位显示，AUF1 不影响根细胞分裂，但促进细胞分裂素介导的伸长/分化区的细胞扩张。上位性分析表明，细胞分裂素调节剂 ARR1 或其效应物（s）是与 AUF1/2 组装的 SKP1-Cullin1-F 框（SCF）泛素连接酶的靶标。鉴于 AUF1/2 型蛋白在陆生植物中的广泛分布，我们提出 SCF（AUF1/2）为生长素和细胞分裂素之间提供了额外的交叉对话，从而改变了生长素的分布，最终影响了根的伸长。
