Ke Danxia, Li Xiangyong, Han Yapeng, Cheng Lin, Yuan Hongyu, Wang Lei
College of Life Sciences & Institute for Conservation and Utilization of Agro-bioresources in Dabie Mountains, Xinyang Normal University, Xinyang 464000, China.
College of Life Sciences & Institute for Conservation and Utilization of Agro-bioresources in Dabie Mountains, Xinyang Normal University, Xinyang 464000, China.
Plant Physiol Biochem. 2016 Nov;108:488-498. doi: 10.1016/j.plaphy.2016.08.015. Epub 2016 Aug 27.
Roots of leguminous plants perceive Nod factor signals, and then root hair deformation responses such as swelling and curling are activated. However, very little is known about the molecular mechanisms of such root hair deformation. We have previously shown that LjROP6, a member of the Rho family of small GTPases, was identified as an NFR5 (Nod Factor Receptor 5)-interacting protein and participated in symbiotic nodulation in Lotus japonicus. In this study, we identified ten LjROP GTPases including LjROP6, and they were distributed into groups II, III, IV but not group I by phylogenetic analysis. The expression profiles of ten LjROP genes during nodulation were examined. LjROP6 belonged to group IV and interacted with NFR5 in a GTP-dependent manner. Overexpression of either wild-type ROP6 or a constitutively active mutant (ROP6-CA) generated root hair tip growth depolarization, while overexpression of a dominant negative mutant (ROP6-DN) exhibited normal root hair growth. After inoculating with Mesorhizobium loti or adding Nod factors to hairy roots, overexpression of ROP6 and ROP6-CA exhibited extensive root hair deformation, while overexpression of ROP6-DN inhibited root hair deformation. The infection event and nodule number were increased in ROP6 and ROP6-CA overexpressing transgenic plants; but decreased in ROP6-DN overexpressing transgenic plants. These studies provide strong evidence that ROP6 GTPase, which binds NFR5 in a GTP-dependent manner, is involved in root hair development as well as root hair deformation responses induced by NFs in the early stage of symbiotic interaction in L. japonicus.
豆科植物的根感知根瘤菌因子信号，随后激活根毛变形反应，如肿胀和卷曲。然而，对于这种根毛变形的分子机制知之甚少。我们之前已经表明，LjROP6是小GTP酶Rho家族的成员，被鉴定为与NFR5（根瘤菌因子受体5）相互作用的蛋白，并参与了百脉根的共生结瘤过程。在本研究中，我们鉴定了包括LjROP6在内的10个LjROP GTP酶，通过系统发育分析，它们被分为第II、III、IV组，而不属于第I组。我们检测了10个LjROP基因在结瘤过程中的表达谱。LjROP6属于第IV组，以GTP依赖的方式与NFR5相互作用。野生型ROP6或组成型激活突变体（ROP6-CA）的过表达导致根毛顶端生长去极化，而显性负突变体（ROP6-DN）的过表达则表现出正常的根毛生长。在用苜蓿中华根瘤菌接种或向毛状根中添加根瘤菌因子后，ROP6和ROP6-CA的过表达表现出广泛的根毛变形，而ROP6-DN的过表达则抑制根毛变形。在过表达ROP6和ROP6-CA的转基因植物中，侵染事件和根瘤数量增加；而在过表达ROP6-DN的转基因植物中则减少。这些研究提供了强有力的证据，表明以GTP依赖方式结合NFR5的ROP6 GTP酶参与了百脉根共生互作早期阶段根毛的发育以及根瘤菌因子诱导的根毛变形反应。
