AtPRK2 Promotes ROP1 Activation via RopGEFs in the Control of Polarized Pollen Tube Growth
AtPRK2 Promotes ROP1 Activation via RopGEFs in the Control of Polarized Pollen Tube Growth
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DOI：
10.1093/mp/sss103
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发表时间：
2013-07-01
期刊：
影响因子：
27.5
通讯作者：
Yang, Zhenbiao
中科院分区：
文献类型：
--
作者：
Chang, Fang;Gu, Ying;Yang, Zhenbiao
拟南芥花粉管中基于ROP 1 GTP酶的信号网络控制顶端生长我们前期的研究表明ROP 1可能被植物特异性的Rho鸟嘌呤核苷酸交换因子（Rho guanine nucleotide exchange factors，RopGEFs）家族成员RopGEF 1直接激活，而RopGEF 1可能通过释放RopGEF 1的自抑制作用被未知因子激活。在这项研究中，我们发现RopGEF 1与ROP 1和AtPRK 2形成复合物，AtPRK 2是一种受体样蛋白激酶，以前被证明与RopGEF相互作用。AtPRK 2在体外磷酸化RopGEF 1，atprk 1，2，5三重突变体表现出与ropgef 1，9，12，14四重突变体相似的花粉管生长缺陷。AtPRK 2（DN-PRK 2）的显性负性形式的过表达抑制拟南芥的花粉萌发和减少烟草的花粉伸长。DN-PRK 2诱导的花粉萌发缺陷通过过表达RopGEF 1的组成型活性形式RopGEF 1（90457）来挽救，这意味着RopGEF 1在AtPRK 2的下游起作用。此外，AtPRK 2增加ROP 1活性在顶端质膜，而DN-PRK 2降低ROP 1活性。最后，在RopGEF 1的C-末端推定磷酸化位点的两个突变（RopGEF 1 S460 A和RopGEF 1 S480 A）消除了RopGEF 1在体内的功能。综上所述，我们的研究结果支持这一假设，AtPRK 2作为一个积极的调节器的ROP 1信号通路最有可能通过激活RopGEF 1通过磷酸化。
The ROP1 GTPase-based signaling network controls tip growth in Arabidopsis pollen tubes. Our previous studies imply that ROP1 might be directly activated by RopGEF1, which belongs to a plant-specific family of Rho guanine nucleotide exchange factors (RopGEFs) and in turn may be activated by an unknown factor through releasing RopGEF1s auto-inhibition. In this study, we found that RopGEF1 forms a complex with ROP1 and AtPRK2, a receptor-like protein kinase previously shown to interact with RopGEFs. AtPRK2 phosphorylated RopGEF1 in vitro and the atprk1,2,5 triple mutant showed defective pollen tube growth, similar to the phenotype of the ropgef1,9,12,14 quadruple mutant. Overexpression of a dominant negative form of AtPRK2 (DN-PRK2) inhibited pollen germination in Arabidopsis and reduced pollen elongation in tobacco. The DN-PRK2-induced pollen germination defect was rescued by overexpressing a constitutively active form of RopGEF1, RopGEF1(90457), implying that RopGEF1 acts downstream of AtPRK2. Moreover, AtPRK2 increased ROP1 activity at the apical plasma membrane whereas DN-PRK2 reduced ROP1 activity. Finally, two mutations at the C-terminal putative phosphorylation sites of RopGEF1 (RopGEF1S460A and RopGEF1S480A) eliminated the function of RopGEF1 in vivo. Taken together, our results support the hypothesis that AtPRK2 acts as a positive regulator of the ROP1 signaling pathway most likely by activating RopGEF1 through phosphorylation.