A SAC phosphoinositide phosphatase controls rice development via hydrolyzing phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate

Abstract

30Phosphoinositides (PIs) as regulatory membrane lipids play essential roles in multiple 31 cellular processes. Although the exact molecular targets of PIs-dependent modulation 32 remain largely elusive, the effects of disturbed PIs metabolism could be employed to 33 propose regulatory modules associated with particular downstream targets of PIs. 34 Here, we identified the role of GRAIN NUMBER AND PLANT HEIGHT 1 (GH1), 35 which encodes a suppressor of actin (SAC) domain-containing phosphatase with 36 unknown function in rice. Endoplasmic reticulum-localized GH1 specifically 37 dephosphorylated and hydrolyzed phosphatidylinositol 4-phosphate (PI4P) and 38 phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. Inactivation of GH1 resulted in 39 massive accumulation of both PI4P and PI(4,5)P2, while excessive GH1 caused their 40 depletion. Notably, superabundant PI4P and PI(4,5)P2 could both disrupt actin 41 cytoskeleton organization and suppress cell elongation. Interestingly, both PI4P and 42 PI(4,5)P2 inhibited actin-related proteins 2 and 3 (Arp2/3) complex-nucleated actin 43 branching networks in vitro, whereas PI(4,5)P2 showed more dramatic effect in a 44 dose-dependent manner. Overall, the overaccumulation of PI(4,5)P2 resulted from 45 dysfunction of SAC phosphatase possibly perturbs Arp2/3 complex-mediated actin 46 polymerization, thereby disordering the cell development. These findings imply that 47 Arp2/3 complex might be the potential molecular target of PI(4,5)P2-dependent 48 modulation in eukaryotes, thereby providing new insights into the relationship 49 between PIs homeostasis and plants growth and development. 50 51 Phosphoinositides (PIs) as a minor component of cell membranes and phosphorylated 52 derivatives of phosphatidylinositol are known to liberate the second messengers, 53 inositol 1,4,5-triphosphate and diacylglycerol in response to activation of cell surface 54 receptors (Boss and Im, 2012). Nevertheless, emerging evidence suggests that PIs also 55 play crucial roles as signaling molecules, functioning as regulatory lipids in various 56 fundamental cellular processes (Heilmann, 2016). A new detection approach further 57 confirmed that phosphatidylinositol 4-phosphate (PI4P) and phosphatidylinositol 58 4,5-bisphosphate [PI(4,5)P2] are the most abundant PIs in the cells (Balla, 2013; 59 Kielkowska et al., 2014). PI4P is phosphorylated by phosphatidylinositol phosphate 60 kinases, resulting in the production of PI(4,5)P2, while conversely PI(4,5)P2 is 61 dephosphorylated by PI phosphatases to generate PI4P, supporting the hypothesis that 62 turnover and dynamic formation of PIs is necessary for plant development (Gerth et 63 al., 2017).64 65 The plant actin cytoskeleton plays essential roles in cell morphogenesis, and the 66 dynamics of actin cytoskeleton drives the membrane deformation and trafficking, 67 which is required for polar cell growth and movement of vesicles and organelles 68 (Pleskot et al., 2014; Wang et al., 2017). This dynamic remodeling is controlled by 69 diverse actin-bin...

iDePP: a genetically encoded system for the inducible depletion of PI(4,5)P2inArabidopsis thaliana

“…For 270 example, depletion of PI(4,5)P2 at the plasma membrane by expressing phosphatases disrupts the actin 271 cytoskeleton leading to a cell-wide reduction in polymerized F-actin in animal cells (Raucher et al, 272 2000;Shibasaki et al, 1997). Since the activity of actin-remodeling protein are known to be regulated 273 by PI(4,5)P2 in plant cell (Gungabissoon et al, 1998;Guo et al, 2019;Huang et al, 2003;Staiger et al, 274 1997), we investigated qualitatively whether PI(4,5)P2 depletion could affect the organization of F-actin 275 cytoskeleton in plant cells in a manner similar to that of animal cells. Using live cell imaging, we 276 observed actin filament in elongated root cell using z-projection of the F-actin marker LifeAct-YFPv 277 before and upon PI(4,5)P2 depletion using iDePP.…”