Submitted to: Plant Signaling and Behavior
Publication Type: Proceedings
Publication Acceptance Date: 12/6/2007
Publication Date: 5/1/2008
Publication URL: www.landesbioscience.com/journals/psb/ZhangPSB3-5.pdf
Citation: Zhang, Y., McCormick, S.M. 2008. Regulation of pollen tube polarity: Feedback loops rule. Plant Signaling and Behavior. 3(5)345-347. Interpretive Summary: This paper proposed a model explaining pollen tube polarity as a combination of two different feedback loops, which is an extension of the work published in Zhang and McCormick, PNAS 104: 18830-18835.
Technical Abstract: Targeted delivery of immotile sperm through growing pollen tubes is a crucial step in achieving sexual reproduction in angiosperms. Unlike diffuse-growing cells, the growth of a pollen tube is restricted to the very apical region where targeted exocytosis and regulated endocytosis occur. The plant-specific Rho GTPases, Rops, are central organizers for pollen tube polarity. Through effector binding, Rops regulate the tip-focused Ca2+ gradient and the actin cytoskeleton during pollen tube growth. Therefore, understanding the spatiotemporal regulation of Rop activity would reveal how establishment and maintenance of tube polarity as well as re-orientation of the growth axis are accomplished. Recent findings indicated that two feedback loops may be fundamental in maintaining a fine-tuned and dynamic Rop activity. The concerted activities of RopGAP and RopGDI prevent lateral diffusion of activated Rop, restricting Rop activity to the apical plasma membrane. Conversely, pollen receptor kinases (PRKs) and RopGEFs positively feedback regulate Rop activity through protein binding and membrane recruitment. Feedback loops would also be essential for pollen tube re-orientation. Shallow extracellular cues amplified by concerted activities of feedback loops would lead to asymmetric activation of Rop and result in tube re-orientation.