Calmodulin Domain Protein Kinase PiCDPK1 Regulates Pollen Tube Growth Polarity through Interaction with RhoGDI

Abstract

The pollen-specific calcium-dependent protein kinase PiCDPK1 of Petunia inflata has previously been shown to regulate polarity in tip growth in pollen tubes. Here we report the identification of a Rho Guanine Dissociation Inhibitor (PiRhoGDI1) as a PiCDPK1 interacting protein. We demonstrate that PiRhoGDI1 and PiCDPK1 interact in a yeast 2-hybrid assay, as well as in an in vitro pull-down assay, and that PiRhoGDI1 is phosphorylated by PiCDPK1 in vitro. We further demonstrate the PiRhoGDI1 is capable of rescuing the loss of growth polarity phenotype caused by over-expressing PiCDPK1 in vivo using stable transgenic plants. We confirmed that PiRhoGDI1 interacts with a pollen-expressed ROP GTPase isoform consistent with the established role of RhoGDIs in negatively regulating GTPases through their membrane removal and locking them in an inactive cytosolic complex. ROP is a central regulator of polarity in tip growth, upstream of Ca2+, and PiCDPK1 over-expression has been previously reported to lead to dramatic elevation of cytosolic Ca2+ through a positive feedback loop. The discovery that PiCDPK1 impacts ROP regulation via PiRhoGDI1 suggests that PiCDPK1 acts as RhoGDI displacement factor and leads us to propose a model which we hypothesize regulates the rapid recycling of ROP GTPase at the pollen tube tip.

Signaling network controlling ROP-mediated tip growth in Arabidopsis and beyond

“…Overexpression of PiCDPK1 induced extremely short pollen tubes with almost spherical tips, resembling those caused by ROP overexpression ( Yoon et al., 2006 ; Scheible et al., 2022 ). Co-expression of PiGDI1 suppressed the depolarized pollen tube growth caused by excess PiCDPK1 , suggesting that PiCDPK1 negatively regulates GDI1 by phosphorylation ( Scheible et al., 2022 ). Although a similar mechanism has not been reported in Arabidopsis , CPK3, a calcium-dependent protein kinase, regulates the development of leaf pavement cells by phosphorylating GDI1 in Arabidopsis ( Wu et al., 2013 ).…”

“…Phosphorylation may also influence the activity of GDIs. A study in Petunia inflata indicated that PiCDPK1, a pollen-specific calcium-dependent protein kinase, interacted with and phosphorylated PiGDI1 ( Figure 1 ) ( Scheible et al., 2022 ). Overexpression of PiCDPK1 induced extremely short pollen tubes with almost spherical tips, resembling those caused by ROP overexpression ( Yoon et al., 2006 ; Scheible et al., 2022 ).…”

“…A study in Petunia inflata indicated that PiCDPK1, a pollen-specific calcium-dependent protein kinase, interacted with and phosphorylated PiGDI1 ( Figure 1 ) ( Scheible et al., 2022 ). Overexpression of PiCDPK1 induced extremely short pollen tubes with almost spherical tips, resembling those caused by ROP overexpression ( Yoon et al., 2006 ; Scheible et al., 2022 ). Co-expression of PiGDI1 suppressed the depolarized pollen tube growth caused by excess PiCDPK1 , suggesting that PiCDPK1 negatively regulates GDI1 by phosphorylation ( Scheible et al., 2022 ).…”

Calmodulin-Domain Protein Kinase PiCDPK1 Interacts with the 14-3-3-like Protein NtGF14 to Modulate Pollen Tube Growth

“…Two CDPKs were identified in Petunia pollen, and one was shown to modulate the polar extension of the tube because its over-expression resulted in swollen spherical tubes [10]. Evidence suggests that this kinase, PiCPDPK1, interacts with a rho guanine dissociation inhibitor (RhoGDI), a negative regulator of Rho GTPase activity, as their co-expression rescues the CDPK over-expression phenotype [11]. Rho GTPase activity is a well-characterized regulator of polar pollen tube growth in Arabidopsis [12].…”

10th Anniversary of Plants—Recent Advances and Further Perspectives

“…are elucidated. This group includes articles [1,2,7,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], communications [27,28], and review papers [5,6,11,[29][30][31][32][33][34] with significant results applicable both in science and practice. The biology and ecology of plant secondary metabolites, their identification, and biological and therapeutic activity from different aspects of the phytochemistry of edible, aromatic, medicinal, or potentially medicinal plants are represented in a significant number of articles [3,8,[35][36][37][38][39][40][41][42][43][44][45][46][47][48][49], as well as review papers [9,50,<...…”