Poster abstracts
Poster number 23 submitted by Tyler Mendes
Identifying motor proteins that function in male germ unit movement in Arabidopsis pollen tubes
Tyler Mendes (Department of Molecular Genetics, The Ohio State University), Iris Meier (Department of Molecular Genetics and Center for RNA Biology, The Ohio State University)
Abstract:
Plant fertilization involves pollen deposition on the stigma of a flower and growth of the pollen tube towards the ovules. The pollen nucleus, termed the vegetative nucleus (VN), migrates down the growing pollen tube along with two male sperm cells (SCs). In Arabidopsis pollen tubes, the VN travels ahead of the SCs down the growing pollen tube. The exact mechanism of this movement is not understood, but previous research has shown that the linker of nucleoskeleton and cytoskeleton (LINC) complexes play a role. The LINC complex spans the inner and outer nuclear membranes and connects the nucleoplasm to the cytoskeleton, either directly or via motor proteins. Null mutants in the genes for two plant LINC complex subunits, WIP and WIT, result in a VN movement defect, wherein the SCs lead while the VN trails behind. This defect correlates with a defect in pollen tube rupture and, in turn, a loss of seed set. We hypothesize that WIT and WIP act as adapter proteins between the VN envelope and unknown pollen cytoskeletal motor proteins. In plants, there are two kinds of cytoskeletal motor proteins: Kinesins (microtubule-associated) and Myosins (actin-associated). To determine which motors are involved in VN movement, we have bioinformatically identified 17 pollen-expressed kinesins (PEK1-17) and 6 pollen-expressed myosins. T-DNA insertional mutants in each gene are being screened for male fertility and VN movement defects. So far, we have identified a mutant in the gene encoding PEK14 that exhibits a fertility defect consistent with that of a WIT null mutant (wit1-1 wit2-1). DAPI staining revealed that in pek14-1 pollen, the order of SCs and VN was reversed in 50% of pollen tubes (95% in wit1-1 wit2-1 pollen tubes). Future experiments will establish if PEK14 is associated with the VN envelope, physically interacts with WIP and WIT, is required for pollen tube rupture, and what its role is in VN and SC transport. Additional motor mutants will also be investigated.
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