AtPRK2 Promotes ROP1 Activation via RopGEFs in the Control of Polarized Pollen Tube Growth

• Published in: Molecular plant Vol. 6; no. 4; pp. 1187 - 1201
• Main Authors: Chang, Fang, Gu, Ying, Ma, Hong, Yang, Zhenbiao
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 01.07.2013; Oxford University Press
• Subjects: Amino Acid Sequence; Arabidopsis - cytology; Arabidopsis - growth & development; Arabidopsis - metabolism; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; AtPRK2; auto-inhibition; Germination; GTP-Binding Proteins - metabolism; Guanine Nucleotide Exchange Factors - chemistry; Guanine Nucleotide Exchange Factors - metabolism; Molecular Sequence Data; Mutation; Phosphorylation; polarity growth; Pollen Tube - growth & development; Protein Kinases - genetics; Protein Kinases - metabolism; ROP GTPase; RopGEF1; Signal Transduction; 信号通路; 偏光; 激活; 磷酸化位点; 网络控制; 花粉管生长; 花粉萌发; 鸟嘌呤核苷酸; RopGEF1; ROP GTPase; polarity growth; auto-inhibition; AtPRK2
• ISSN: 1674-2052; 1752-9867
• DOI: 10.1093/mp/sss103

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 RopGEFI＇s 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 atprkl,2,5 tri- ple 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（90-457）, 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 regula- tor of the ROP1 signaling pathway most likely by activating RopGEF1 through phosphorylation.