Poster abstracts
Poster number 26 submitted by Isabella Mendes
Identifying motor proteins that function in male germ unit movement in Arabidopsis thaliana pollen tubes
Isabella Mendes (Molecular, Cellular, and Developmental Biology Graduate Program, The Ohio State University, Columbus, OH, USA, Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA ), Norman R Groves (Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA, Center for Applied Plant Sciences, The Ohio State University, Columbus, OH, USA), Iris Meier (Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA, Center for Applied Plant Sciences, The Ohio State University, Columbus, OH, USA, Center for RNA Biology, The Ohio State )
Abstract:
Fertilization is a key component of plant reproduction that is necessary for agriculture. While the basic process of fertilization has been understood for centuries, the mechanism underlying how plant sperm is trafficked to the egg remains poorly understood. To achieve fertilization, the growing pollen tube transports the sperm cell (SCs) to ovules. The SCs are physically connected via a cytoplasmic projection from the lead sperm cell to the vegetative nucleus (VN); this combined complex is referred to as the Male Germ Unit (MGU). Previous research has shown that Linker of Nucleoskeleton and Cytoskeleton (LINC) complexes at the VN nuclear envelope facilitate MGU movement. The LINC complex spans the inner and outer nuclear membranes and connects the nucleoplasm to the cytoskeleton. Null mutants in genes for two plant LINC complex subunits, WIP and WIT, result in a VN movement defect, wherein the SCs lead the MGU through the pollen tube while the VN trails behind. This defect correlates with a defect in pollen tube burst and, in turn, a loss of seed set. We hypothesize that WIT and WIP act as adapter proteins between the VN envelope and unknown cytoskeletal motor proteins. In plants, there are two kinds of cytoskeletal motor proteins: Kinesins and Myosins. While Myosins have been well-studied in pollen-tube tip growth, the role of Kinesins in pollen tubes has not been established. To determine which motors are involved in VN movement, we have screened insertional mutants in 17 pollen-expressed Kinesins (PEK1-17) for fertility defects. Kinesin-14s represent a significant portion of the identified kinesins, with 8 of the 17 PEKs being Kinesin-14s. Two of these Kinesin-14s, PEK3 and PEK9, present mild fertility defects in insertional mutants. PEK3 and PEK9 are likely the result of a gene duplication event, leading to the possibility that a more severe fertility defect would be observed in a double mutant. Insertional mutants in a Kinesin-4, PEK14, displayed significant reductions in seed set, on the order of the reduction observed in wit mutants, indicating it may play a role in MGU movement. Future experiments will endeavor to determine the functional role of these motors in pollen and establish if these genes are associated with the VN envelope, physically interact with WIP and/or WIT, or are required for pollen tube burst.
References:
1. Zhou, X., and Meier, I. (2014). “Efficient Plant Male Fertility Depends on Vegetative Nuclear Movement Mediated by Two Families of Plant Outer Nuclear Membrane Proteins.” Proc. Natl. Acad. Sci. USA. 111:32, 11900-11905.
2. Zhou, X., et al. (2012). “Novel Plant SUN-KASH Bridges Are Involved in RanGAP Anchoring and Nuclear Shape Determination.” J Cell Biol. 196:2, 203-211.
3. Zhou, X., et al. (2015). “Plant Nuclear Shape Is Independently Determined by the SUN-WIP-WIT2-Myosin XI-i Complex and CRWN1.” Nucleus. 6:2, 144-153.
4. Cai G, Cresti M. (2009). “Organelle motility in the pollen tube: a tale of 20 years.” Journal of Experimental Botany. 60(2):495-508.
5. Heslop-Harrison J, et al. (1988) “Cytoskeletal elements, cell shaping and movement in the angiosperm pollen-tube.” Journal of Cell Science. 91:49-60.
Keywords: Male Germ Unit, Pollen Tube, Kinesin