Double fertilization in angiosperms requires the targeted delivery of immotile sperm to the eggs through pollen tubes. The polarity of tip-growing pollen tubes is maintained through dynamic association of active Rho G...Double fertilization in angiosperms requires the targeted delivery of immotile sperm to the eggs through pollen tubes. The polarity of tip-growing pollen tubes is maintained through dynamic association of active Rho GTPases of plants （ROP-GTP） with the apical plasma membrane. Guanine nucleotide exchange factors for ROPs （RopGEFs） catalyze the activation of ROPs and thereby affect spatiotemporal ROP signaling. Whereas RopGEFs have been found to be phosphorylated proteins, the kinases responsible for their phos- phorylation in v/vo and biological consequences of RopGEF phosphorylation in pollen tube growth remain unclear. We report here that the Arabidopsis AGC1.5 subfamily of cytoplasmic kinases is critical for the restricted localization of ROP-GTP during pollen tube growth. Loss of AGCI.5 and AGC1.7 functions resulted in the mistargeting of active ROPs and defective events downstream of ROP signaling in pollen tubes. AGCI.5 interacts with RopGEFs via their catalytic PRONE domain and phosphorylates RopGEFs at a conserved Ser residue of PRONE domain. Loss of AGC1.5 and AGC1.7 functions resulted in the mistargeting of RopGEFs in pollen tubes, similar to the phenotype caused by the mutation that renders RopGEFs non-phosphorylatable by AGC1.5. Collectively, our results provide mechanistic insights into the spatiotem- poral activation of ROPs during the polar growth of pollen tubes.展开更多
Tip growth is a special type of polarized growth in which a single and unique polarization site is established and maintained.Rho of Plants(ROP)proteins,which represent the only class of Rho GTPases in plants,regulate...Tip growth is a special type of polarized growth in which a single and unique polarization site is established and maintained.Rho of Plants(ROP)proteins,which represent the only class of Rho GTPases in plants,regulate tip growth.The dynamic and asymmetric distribution of ROPs is critical for the establishment and maintenance of tip growth,and requires at least one positive feedback loop,which is still elusive.Here,we report a positive feedback circuit essential for tip growth of root hairs,in which ROPs,ROP activators and effectors,and AGC1.5 subfamily kinases are interconnected by sequential oligomerization and phosphorylation.AGC1.5 subfamily kinases interact with and phosphorylate two guanine nucleotide exchange factors(GEFs)of ROPs,RopGEF4 and RopGEF10.They also interact with two ROP effectors,ICR2/RIP3 and MIDD1/RIP4,which bridge active ROPs with AGC1.5.Functional loss of the AGC1.5 subfamily kinases or ICR2 and MIDD1 compromised root hair growth due to reduced ROP signaling.We found that asymmetric targeting of RopGEF4 and RopGEF10 is controlled by AGC1.5-dependent phosphorylation.Interestingly,we discovered that the ROP effectors recruit AGC1.5 to active ROP domains at the plasma membrane during root hair growth and are critical for AGC1.5-dependent phosphorylation of RopGEFs.Given the large number of AGC kinases in plants,this positive feedback circuit may be a universal theme for plant cell polar growth.展开更多
基金This research was supported by the National Natural Science Foundation of China （31471304 to Y.Z. 31771558 to S.L.）, Natural Science Foundation of Shandong Province （ZR2014CM027 to S.L.）, China Postdoctoral Science Foundation （2018M632698 to E.L.）, and Research Grants Council of Hong Kong （AoE/M-05/12 and C4011-14R）. Y.Z. was partially supported by the Tai-Shan Scholar program from the Shandong Provinciak Government.
文摘Double fertilization in angiosperms requires the targeted delivery of immotile sperm to the eggs through pollen tubes. The polarity of tip-growing pollen tubes is maintained through dynamic association of active Rho GTPases of plants （ROP-GTP） with the apical plasma membrane. Guanine nucleotide exchange factors for ROPs （RopGEFs） catalyze the activation of ROPs and thereby affect spatiotemporal ROP signaling. Whereas RopGEFs have been found to be phosphorylated proteins, the kinases responsible for their phos- phorylation in v/vo and biological consequences of RopGEF phosphorylation in pollen tube growth remain unclear. We report here that the Arabidopsis AGC1.5 subfamily of cytoplasmic kinases is critical for the restricted localization of ROP-GTP during pollen tube growth. Loss of AGCI.5 and AGC1.7 functions resulted in the mistargeting of active ROPs and defective events downstream of ROP signaling in pollen tubes. AGCI.5 interacts with RopGEFs via their catalytic PRONE domain and phosphorylates RopGEFs at a conserved Ser residue of PRONE domain. Loss of AGC1.5 and AGC1.7 functions resulted in the mistargeting of RopGEFs in pollen tubes, similar to the phenotype caused by the mutation that renders RopGEFs non-phosphorylatable by AGC1.5. Collectively, our results provide mechanistic insights into the spatiotem- poral activation of ROPs during the polar growth of pollen tubes.
基金This work is funded by National Natural Science Foundation of China(31625003,31271578,31871422 to Y.Z.,31771558 and 31970332 to S.L.)Yan Zhang's lab is partially supported by Tai-Shan Scholar program by Shandong Provincial Government.
文摘Tip growth is a special type of polarized growth in which a single and unique polarization site is established and maintained.Rho of Plants(ROP)proteins,which represent the only class of Rho GTPases in plants,regulate tip growth.The dynamic and asymmetric distribution of ROPs is critical for the establishment and maintenance of tip growth,and requires at least one positive feedback loop,which is still elusive.Here,we report a positive feedback circuit essential for tip growth of root hairs,in which ROPs,ROP activators and effectors,and AGC1.5 subfamily kinases are interconnected by sequential oligomerization and phosphorylation.AGC1.5 subfamily kinases interact with and phosphorylate two guanine nucleotide exchange factors(GEFs)of ROPs,RopGEF4 and RopGEF10.They also interact with two ROP effectors,ICR2/RIP3 and MIDD1/RIP4,which bridge active ROPs with AGC1.5.Functional loss of the AGC1.5 subfamily kinases or ICR2 and MIDD1 compromised root hair growth due to reduced ROP signaling.We found that asymmetric targeting of RopGEF4 and RopGEF10 is controlled by AGC1.5-dependent phosphorylation.Interestingly,we discovered that the ROP effectors recruit AGC1.5 to active ROP domains at the plasma membrane during root hair growth and are critical for AGC1.5-dependent phosphorylation of RopGEFs.Given the large number of AGC kinases in plants,this positive feedback circuit may be a universal theme for plant cell polar growth.
