SCARN a Novel Class of SCAR Protein That Is Required for Root-Hair Infection during Legume Nodulation.
SCARN a Novel Class of SCAR Protein That Is Required for Root-Hair Infection during Legume Nodulation.
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DOI：
10.1371/journal.pgen.1005623
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发表时间：
2015-10
期刊：
影响因子：
4.5
通讯作者：
Xie F
中科院分区：
文献类型：
--
作者：
Qiu L;Lin JS;Xu J;Sato S;Parniske M;Wang TL;Downie JA;Xie F
根瘤菌对豆科植物根毛的感染需要肌动蛋白细胞骨架的重排，以建立植物制造的感染结构，称为感染丝。在SCAR/WAVE（Suppressor of cAMP receptor defect/WASP family verpolin homologous protein）肌动蛋白调节复合物中，SCAR蛋白的保守N-末端结构域与SCAR/WAVE复合物的其他组分相互作用。SCAR蛋白的保守C-末端结构域结合并激活肌动蛋白相关蛋白2/3（ARP 2/3）复合物，其可以结合肌动蛋白丝，通过使肌动蛋白分支成核来催化新的肌动蛋白丝形成。我们已经确定，SCARN（SCAR-Nodulation），一个基因所需的根毛感染莲花中慢生根瘤菌。虽然SCARN蛋白与拟南芥SCAR 2和SCAR 4相关，但它属于一个不同的豆科亚支。我们在豆科植物中鉴定出了其他SCARN样蛋白，并进行了遗传分析，结果表明SCARN可能是由基因复制引起的，并在根瘤共生中获得了专门的功能。SCARN的突变减少了侵染线的形成及其向根皮层的延伸，并略微减少了根毛长度。令人惊讶的是，两个scarn突变体在未接种的植物中表现出根毛的组成性分支。然而，我们没有观察到瘢痕突变对毛状体发育或早期肌动蛋白细胞骨架积累的影响，而这种积累通常在M. loti接种，区别于其他共生突变影响肌动蛋白成核。SCARN的C-末端结构域与ARPC 3结合，并且N-末端SCAR同源结构域（但不是全长蛋白）的异位表达抑制了增殖。此外，我们发现SCARN的表达被M. loti在表皮细胞中的表达，并且这直接受NODINCEPTION（NIN）转录因子的调节。对根瘤菌感染的百脉根突变体的特征鉴定导致了我们命名为SCARN的基因的鉴定。五个等位基因中的两个引起未接种幼苗的分支根毛的形成，表明SCARN在微管和肌动蛋白调节的根毛极性生长中起作用。Scarn是三个L之一。包含保守的N和C末端结构域的肌动蛋白类，推测为肌动蛋白细胞骨架重排所需。SCARN的表达是由NIN（NODITINCEPTION）转录因子响应根瘤菌的促生长因子而诱导的，并且似乎适应于促进根瘤菌感染，这可能是由基因复制事件引起的。SCARN与ARPC 3结合，ARPC 3是参与肌动蛋白成核活化的肌动蛋白相关蛋白复合物中的预测组分之一。
Rhizobial infection of legume root hairs requires a rearrangement of the actin cytoskeleton to enable the establishment of plant-made infection structures called infection threads. In the SCAR/WAVE (Suppressor of cAMP receptor defect/WASP family verpolin homologous protein) actin regulatory complex, the conserved N-terminal domains of SCAR proteins interact with other components of the SCAR/WAVE complex. The conserved C-terminal domains of SCAR proteins bind to and activate the actin-related protein 2/3 (ARP2/3) complex, which can bind to actin filaments catalyzing new actin filament formation by nucleating actin branching. We have identified, SCARN (SCAR-Nodulation), a gene required for root hair infection of Lotus japonicus by Mesorhizobium loti. Although the SCARN protein is related to Arabidopsis thaliana SCAR2 and SCAR4, it belongs to a distinct legume-sub clade. We identified other SCARN-like proteins in legumes and phylogeny analyses suggested that SCARN may have arisen from a gene duplication and acquired specialized functions in root nodule symbiosis. Mutation of SCARN reduced formation of infection-threads and their extension into the root cortex and slightly reduced root-hair length. Surprisingly two of the scarn mutants showed constitutive branching of root hairs in uninoculated plants. However we observed no effect of scarn mutations on trichome development or on the early actin cytoskeletal accumulation that is normally seen in root hair tips shortly after M. loti inoculation, distinguishing them from other symbiosis mutations affecting actin nucleation. The C-terminal domain of SCARN binds to ARPC3 and ectopic expression of the N-terminal SCAR-homology domain (but not the full length protein) inhibited nodulation. In addition, we found that SCARN expression is enhanced by M. loti in epidermal cells and that this is directly regulated by the NODULE INCEPTION (NIN) transcription factor. Characterization of Lotus japonicus mutants defective for nodule infection by rhizobia led to the identification of a gene we named SCARN. Two of the five alleles caused formation of branched root-hairs in uninoculated seedlings, suggesting SCARN plays a role in the microtubule and actin-regulated polar growth of root hairs. SCARN is one of three L. japonicus proteins containing the conserved N and C terminal domains predicted to be required for rearrangement of the actin cytoskeleton. SCARN expression is induced in response to rhizobial nodulation factors by the NIN (NODULE INCEPTION) transcription factor and appears to be adapted to promoting rhizobial infection, possibly arising from a gene duplication event. SCARN binds to ARPC3, one of the predicted components in the actin-related protein complex involved in the activation of actin nucleation.