title: RIP1 (ROP Interactive Partner 1)/ICR1 marks pollen germination sites and may act in the ROP1 pathway in the control of polarized pollen growth.
abstract: Rho family small GTPases are universal signaling switches in the control of cell polarity in eukaryotic cells. Their polar distribution to the cell cortex is critical for the execution of their functions, yet the mechanism for this distribution is poorly understood. Using a yeast two-hybrid method, we identified RIP1 (ROP interactive partner 1), which belongs to a family of five members of novel proteins that share a C-terminal region that interacts with ROP. When expressed in Arabidopsis pollen, green fluorescence protein GFP-tagged RIP1 was localized to the nucleus of mature pollen. When pollen grains were hydrated in germination medium, GFP-RIP1 switched from the nucleus to the cell cortex at the future pollen germination site and was maintained in the apical cortex of germinating pollen and growing pollen tubes. RIP1 was found to interact with ROP1 in pollen tubes, and the cortical RIP1 localization was influenced by the activity of ROP1. Overexpression of RIP1 induced growth depolarization in pollen tubes, a phenotype similar to that induced by ROP1 overexpression. Interestingly, RIP1 overexpression enhanced GFP-ROP1 recruitment to the plasma membrane (PM) of pollen tubes. Based on these observations, we hypothesize that RIP1 is involved in the positive feedback regulation of ROP1 localization to the PM, leading to the establishment of a polar site for pollen germination and pollen tube growth.
authors.affiliation: Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA.
authors.forename: Shundai
authors.initials: S
authors.lastname: Li
authors.forename: Ying
authors.initials: Y
authors.lastname: Gu
authors.forename: An
authors.initials: A
authors.lastname: Yan
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Lord
authors.forename: Zhen-Biao
authors.initials: ZB
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity; D031541:Fluorescence Resonance Energy Transfer; D019204:GTP-Binding Proteins / Q000378:metabolism*; D018525:Germination / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011058:Pollen / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D053205:Pollen Tube / Q000166:cytology / Q000254:growth & development; D011485:Protein Binding; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D014026:Nicotiana / Q000166:cytology / Q000378:metabolism; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; C522443:ICR1 protein, Arabidopsis; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D019204:GTP-Binding Proteins; C501663:ROP1 protein, Arabidopsis