Download presentation
Presentation is loading. Please wait.
1
Oscillations in Pollen Tube Growth & ROP Signaling Network Oscillations in Pollen Tube Growth & ROP Signaling Network XIA, Fan
2
Introduction Observation of oscillations in pollen tube: Observation of oscillations in pollen tube: Spontaneous Positive correlation between oscillation and the rate of growth. Phase relationship Mechanism underlying these oscillations: Mechanism underlying these oscillations: The oscillations with a period of minutes or shorter can are unlikely to involve periodic changes in gene expression. ROP1 signaling network plays a key role. 0°: tip F-actin & ROP1 activity 90 ° : Growth rate 120 ° : Calcium concentration 210 ° : Calcium influx
4
ROP1 Signaling Network ROP1 Signaling Network Jae-Ung Hwang et al., 2005 ROP1 ROP1 Location of the active ROP1 establish the tip growth domain. Recruitment: A tip- localized recruitment factor and a tip-localized Rop sequestering factor (AtGDI1). Maintenance: active ROP1 promotes the recruitment to the apical PM region.
6
Oscillation of ROP1 activity Oscillation of ROP1 activity RIC4 localization to the apical cap, i.e., the apparent tip-localized ROP1 activity, is oscillatory and leads growth bursts by 90 °. Experiment RIC4 localization to the PM is the direct result of its binding to the active form of ROP1. RIC4∆C loses the effort function of RIC4 in the promotion of F-actin assembly, but faithfully reports its interaction with active ROP1. Intensity of RIC4∆C at PM reflects the activity of ROP1. Result
7
RIC3 and RIC4 RIC3 and RIC4 RICs: ROP-interactive CRIB-containing proteins. In pollen tubes, only RIC3 and RIC4 OX induced depolarized growth. o Structurally different o Two different pathways Interaction with ROP1 o Only interact with active form o Recruit from the cytoplasm to the PM o While RIC4 is tightly associated with PM domain, RIC3 is primarily cytoplasmic. RIC3 interacts with ROP1 in transient and dynamic manner, as AtGDI1.
10
RIC4 downstream pathway RIC4 downstream pathway Similar to ROP1OX, RIC4OX induced dense F- actin network and depolarization. LatB could recover the oscillation of tip F-actin in RIC4OX tubes. RIC4 promotes the actin assembly.
11
RIC3 downstream pathway RIC3 downstream pathway Similar to high [Ca 2+ ] ex, RIC3OX induced loss of F-actin and protrusion of the axial actin cables toward the extreme apex. EGTA and LaCl 3 could recover RIC3OX induced growth inhibition and actin reorganization. RIC3 affects [Ca 2+ ] ex influx.
12
Counteract between the two pathways Counteract between the two pathways RIC3OX and RIC4OX resulted in the recovery of growth.---antagonistic effect Optimal ratio RIC3/RIC4 = 1:2 Not due to the competition to bind to ROP1 but due to downstream targets. o Different location of action o RIC3 acts through Ca 2+ to promote the disassembly of RIC4- dependent F-actin. o RIC4 acts through F-actin to counteract the RIC3 pathway.
13
F-actin feedback to ROP1 activity F-actin feedback to ROP1 activity LatB treatments recovered the polarized growth in both ROP1OX and RIC4OX. LatB treatments significantly reduced the peak of GFP- RIC4∆C localization/ROP1 activity. Mechanism unknown. Analog in other system. [Ca 2+ ] cyc feedback to ROP1 activity [Ca 2+ ] cyc feedback to ROP1 activity Possible down regulation above threshold. Mechanism unknown. Common interaction between Ca2+ and GEFs, GAPs and GDIs.
14
Quantitative Modeling Quantitative Modeling Target: o Oscillation with proper phase relationship between ROP activity, F-actin and [Ca 2+ ] cyc. o Mutant experiment (OX elimination of oscillation)
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.