Relocalization of the PIN1 auxin efflux facilitator plays a role in phototropic responses
Relocalization of the PIN1 auxin efflux facilitator plays a role in phototropic responses
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DOI：
10.1104/pp.103.031690
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发表时间：
2004-01-01
期刊：
影响因子：
7.4
通讯作者：
Murphy, AS
中科院分区：
文献类型：
--
作者：
Blakeslee, JJ;Bandyopadhyay, A;Murphy, AS
最近，我们报道了在黑暗或单向光下生长的拟南芥mdr（pgp）突变体的下胚轴中，PIN 1生长素流出促进蛋白的基础定位被破坏（Noh等，2003年）。分子遗传学和生理学证据表明，PIN 1是生长素从芽向根尖运输所必需的（Okada et al.，一九九一年; Friml和Palme，2002），而免疫组织化学研究将PIN 1定位于芽和根中木质部相关细胞的下端（Gälweiler等人，1998年）。最近，已经显示根尖中的不对称PIN 1定位涉及由ARF-GEF GNOME介导的动态循环（Geldner等人，2001年、2003年）。令人惊讶的是，尽管MDR/PGP基因的破坏导致极性生长素转运减少（Noh等人，2001; Geisler等人，2003; Multani等人，2003）和下部茎和根组织中游离生长素含量降低（JJ Blakeslee和AS Murphy，未发表的数据），mdr 1 pgp 1突变体下胚轴表现出过度的向性弯曲（Noh等人，2003年）。根据Cholodny-Went假说（参见Went，1974），向性弯曲是由靠近向性刺激位点的生长素的侧向再分布介导的。我们的报告表明，增强热带弯曲观察mdr/pgp突变体导致垂直运输生长素减少，从而增加了横向生长素的偏见。然而，目前尚不清楚是否干扰的PIN 1定位在MDR/Pgp突变体是由于中断的立即相互作用所需的不对称定位的PIN 1蛋白或从累积的发育缺陷所造成的生长素转运改变。在AtMDR 1和AtPGP 1不表达的组织中，改变的局部生长素水平可能在多大程度上有助于PIN 1的离域也没有确定。为了确定是否PIN 1的离域类似于在超向光性MDR/Pgp突变体中看到的也在正常的向光性反应中起作用，我们研究了在野生型（WT）幼苗响应于450 nm蓝光的第一个正向光性曲率开始后PIN 1定位的变化。当用定向蓝光照射时，拟南芥幼苗表现出涉及两个步骤的向光弯曲反应-垂直生长的初始停止和随后的弯曲起始（Parks等人，2001年）。由蓝光的趋光蛋白感知引发的信号转导途径（Briggs等人，2001）并由Ca 2+调节（Harada et al.，2003; Stoelzle等人，2003）和蛋白质信号传导组分（Motchoulski和Liscum，1999）已经显示介导弯曲反应。尽管定向蓝光被认为在下胚轴的上部被感知（Parks等人，2001），弯曲表现在中下胚轴区域，并且被认为是由生长素流出通过侧向取向的PIN 3生长素流出促进剂调节的（Friml等人，2002年）。当WT幼苗在黑暗中生长时，其中观察到PIN 1的基底定位（图1A），随后暴露于单向蓝光（0.5 μmol m J2 s J1，450 nm，持续1.5 h），我们观察到幼苗的向光性弯曲类似于先前描述的（Briggs等人，2001; Friml等人，2002年）。在蓝光刺激后，组织被快速固定，并且通过免疫荧光显微镜定位PIN 1和PIN 3蛋白。尽管无法检测到PIN 3定位的变化（数据未显示），但我们在下胚轴中部区域观察到PIN 1离域（图1B），其中发生向光弯曲，并且之前已证明作为该反应的一部分积累了生长素（Friml等人）。，2002年）。PIN 1中的梯度.
Recently, we reported that the basal localization of the PIN1 auxin efflux facilitator protein is disrupted in hypocotyls of Arabidopsis mdr (pgp) mutants grown in the dark or unidirectional light (Noh et al., 2003). Molecular genetic and physiological evidence indicates that PIN1 is required for transport of auxin from shoot to root apices (Okada et al., 1991; Friml and Palme, 2002), whereas immunohistochemical studies localize PIN1 to the lower ends of xylemassociated cells in both shoots and roots (Gälweiler et al., 1998). More recently, asymmetric PIN1 localization in root tips has been shown to involve dynamic cycling mediated by the ARF-GEF GNOM (Geldner et al., 2001, 2003). Surprisingly, although disruption of MDR/PGP genes results in decreased polar auxin transport (Noh et al., 2001; Geisler et al., 2003; Multani et al., 2003) and decreased free auxin content in lower shoot and root tissues (JJ Blakeslee and AS Murphy, unpublished data), mdr1 pgp1 mutant hypocotyls exhibit exaggerated tropic bending (Noh et al., 2003). According to the Cholodny-Went hypothesis (for summary, see Went, 1974), tropic bending is mediated by lateral redistribution of auxin near the site of tropic stimulus. Our report suggested that the enhanced tropic bending observed in mdr/pgp mutants resulted from decreased vertical auxin transport and a consequent increase of lateral auxin bias. However, it was not clear whether the perturbation of PIN1 localization in mdr/pgp mutants was due to disruption of an immediate interaction required for asymmetric localization of the PIN1 protein or from cumulative developmental defects resulting from altered auxin transport. The extent to which altered localized auxin levels might contribute to PIN1 delocalization in tissues where AtMDR1 and AtPGP1 are not expressed was also not determined. To determine whether PIN1 delocalization similar to that seen in hyper-phototropic mdr/pgp mutants also plays a role in the normal phototropic response, we investigated changes in PIN1 localization after initiation of the first positive phototropic curvature in wild-type (WT) seedlings responding to 450 nm of blue light. When illuminated with directional blue light, Arabidopsis seedlings exhibit a phototropic bending response that involves two steps—an initial halt in vertical growth and subsequent initiation of bending (Parks et al., 2001). A signal transduction pathway initiated by phototropin perception of blue light (Briggs et al., 2001) and modulated by both Ca2+(Harada et al., 2003; Stoelzle et al., 2003) and protein signaling components (Motchoulski and Liscum, 1999) has been shown to mediate the bending response. Although directional blue light is thought to be perceived in the upper portion of the hypocotyl (Parks et al., 2001), bending manifests in the midhypocotyl region and is thought to be regulated by auxin efflux through the laterally oriented PIN3 auxin efflux facilitator (Friml et al., 2002). When WT seedlings were grown in the dark, where basal localization of PIN1 was observed (Fig. 1A), and subsequently exposed to unidirectional blue light (0.5 μmol m J2 s J1, 450 nm, for 1.5 h), we observed phototropic bending of seedlings similar to that previously described (Briggs et al., 2001; Friml et al., 2002). After blue light stimulus, tissues were rapidly fixed, and both PIN1 and PIN3 proteins were localized by immunofluorescence microscopy. Although no changes in PIN3 localization could be detected (data not shown), we observed PIN1 delocalization (Fig. 1B) in the mid-hypocotyl region where phototropic bending occurs and has been shown previously to accumulate auxin as part of that response (Friml et al., 2002). A gradient in PIN1 …