Poster abstracts

Poster number 37 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, Columbus, Ohio), Iris Meier (Department of Molecular Genetics, The Ohio State University, Columbus, Ohio)

Abstract:
When plant fertilization occurs, pollen is deposited on the stigma of a flower and subsequently germinates, forming a pollen tube that grows towards the ovules. The nucleus of this cell, termed the vegetative nucleus (VN), is transported down the pollen tube as it grows, along with two male generative cells (GCs). Together, the two GCs and the VN are termed the male germ unit (MGU). In wild type Arabidopsis pollen, the VN travels in front of the GCs down the growing pollen tube1. The exact mechanism of the movement of the MGU is not understood, but previous research has shown that LINC complexes play a role2. The LINC complex spans the nuclear membrane and connects the nucleus to the cytoskeleton, either directly or via motor proteins2. Null mutants in the genes that encode two component proteins of this complex, WIP and WIT, result in a VN movement defect that manifests as nuclear order switching, wherein the GCs lead while the VN trails behind1. This, in turn, leads to a male fertility defect. It is likely that WIT acts here as an adapter between the nuclear membrane and cytoskeletal motor proteins, as it has a similar function in root hairs3. However, the motor protein(s) that act in VN movement in Arabidopsis have not been identified. 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. Of these, we have so far identified a mutant in the gene encoding PEK14 that exhibits a fertility defect consistent with that of a WIT null mutant (wit12). DAPI staining revealed that pek14 pollen exhibits an intermediate nuclear order switching phenotype, with order being reversed in 50% of pollen tubes (95% in wit12 pollen tubes). Future experiments will establish if PEK14 physically interacts with WIP and WIT and further characterize the role of PEK14 in MGU transport. Additionally, we are continuing to screen for additional motor proteins that may play a role in GC delivery.

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.

Keywords: Pollen , Plant cell biology, Motor proteins