背景回顾：Root hairs (RHs) function in nutrient and water acquisition, root metabolite exudation, soil anchorage and plant-microbe interactions. Longer or more abundant RHs are potential breeding traits for developing crops that are more resource-use efficient and can improve soil health. 

提出问题：While many genes are known to promote RH elongation, relatively little is known about genes and mechanisms that constrain RH growth. 

主要发现：Here we demonstrate that a DOMAIN OF UNKNOWN FUNCTION 506 (DUF506) protein, AT3G25240, negatively regulates Arabidopsis thaliana RH growth. 

结果1-P缺乏诱导表达：The AT3G25240 gene is strongly and specifically induced during P-limitation. 

结果2-功能缺失突变+过表达表型：Mutants of this gene, which we call REPRESSOR OF EXCESSIVE ROOT HAIR ELONGATION 1 (RXR1), have much longer RHs, higher Pi content and seedling biomass, while over-expression of the gene exhibits opposite phenotypes. 

结果3-RXR1互作蛋白：Co-immunoprecipitation, pull-down and BiFC analyses reveal that RXR1 physically interacts with a RabD2c GTPase in nucleus, and arabd2c mutant phenocopies the rxr1 mutant.

结果4-功能域：Furthermore, N-terminal variable region of RXR1 is crucial for inhibiting RH growth. 

结果4-演化保守性：Overexpression of a Brachypodium distachyon RXR1 homolog results in repression of RH elongation in Brachypodium. 

结论：Taken together, our results reveal a novel DUF506-GTPase module with a prominent role in repression of plant RH elongation especially under P stress.

 摘 要 

植物的根毛作用于营养和水分的获取、根代谢物的分泌、土壤锚定以及植物-微生物互作。更长或者更多的根毛是开发资源利用效率更高的作物品种的潜在育种性状，并且有助于改善土壤的健康水平。虽然有很多基因与根毛的伸长有关，但是有关限制根毛生长的基因和分子机制鲜有报道。本文中，作者发现拟南芥中的一个DUF506蛋白（AT3G25240）负调控拟南芥的根毛生长。AT3G25240基因特异性地受到磷缺乏的强烈诱导。AT3G25240基因的功能突变会导致根毛变长、植株磷含量增加以及幼苗的生物量增加；而过表达该基因则会表现出完全相反的表型，因此作者将其命名为根毛过度伸长抑制因子RXR1。免疫共沉淀、pull-down实验以及双分子荧光互补（BiFC）实验表明，RXR1能够与一个RabD2c GTPase在核中发生物理互作，arabd2c突变体的表型与rxr1突变体类似。此外，RXR1蛋白N端高度变异区对于其抑制根毛生长的功能至关重要。过表达短柄草RXR1同源基因会导致短柄草的根毛伸长受到抑制。综上，本文的结果揭示了一个新的DUF506-GTPase模块，在磷缺乏胁迫下作用于植物根毛伸长的限制。

 通讯作者 

** Wolf-Rüdiger Scheible **