Interactions Between Calcium and ROP Signaling Regulate Pollen Tube Tip Growth
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The pollen tube has long been a favorite system to investigate the regulation and function of the spatiotemporal calcium signal in plants. Calcium is critical for polarized cell growth in pollen tubes, termed tip growth, and its intracellular accumulation at the tip region of pollen tubes displays a tip-high gradient and an oscillatory pattern that is tightly correlated with growth oscillation. One calcium oscillator in pollen tube is a ROP GTPase, which belongs to a conserved Rho family of small GTPases. Active ROP1 oscillates in a phase ahead of growth oscillation, and the distribution of active ROP1 to the apical plasma membrane defines tip growth site and is required for pollen tube growth. This polarized growth depends on many factors including active ROP1-regulated downstream factors: F-actin dynamics and tip-focused calcium gradients. These downstream elements are in turn involved in positive and negative feedback regulations of ROP1, respectively. In addition, ROP1 activity is regulated both spatially and temporally by several regulatory proteins, which may be regulated by calcium.
KeywordsPollen Tube Pollen Tube Growth Growth Oscillation Lily Pollen Tube Apical ROP1
Work in the Yang laboratory is supported by funding from Department of Energy and National Institute of Health. We thank members of the Yang laboratory for stimulating discussions.
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