| In lily, two mechanisms were proposed for pollen tube guidance through the pistil: chemotropism (chemotaxis) on the stigma (Kim et al., 2003) and adhesion (haptotactic guidance) in the style (Jauh et al., 1997). Secreted proteins from the lily pistil have been identified for pollen tube chemotropism and adhesion by use of in vitro assays. One is chemocyanin, the first known chemotropic peptide in plants (Kim et al., 2003), and the other is SCA (Stigma/stylar cysteine-rich adhesin) (Park et al., 2000). There are homologues to these two proteins found in the model plant Arabidopsis, plantacyanin for chemocyanin and nsLTPs (non-specific lipid transfer proteins) for SCA, respectively. In this dissertation, molecular and genetic tools are utilized to analyze the functions of plantacyanin and two nsLTPs (AtLTP3 and AtLTP4) in Arabidopsis.; Chapter 1 examines the functions of Arabidopsis plantacyanin in plant reproduction. The recombinant protein HISplantacyanin shows a chemotropic effect on lily pollen tubes (Appendix B) indicating that Arabidopsis plantacyanin may function in a similar way as does lily chemocyanin. Arabidopsis plantacyanin is expressed most highly in the transmitting tract of the pistil with a steep gradient from the stigma into the style and the ovary. Disruption of this gradient by overexpression of plantacyanin in the whole pistil caused pollen tube misguidance on the Arabidopsis stigma. A high level of plantacyanin in anthers led to a lack of anther dehiscence. This appears to be caused by defects in lignin formation and the degeneration of the endothecium (Appendix B). Regulation of plantacyanin, as a putative target of miR408, was also studied in transgenic plants expressing different forms of promoter-GUS translational fusions (Appendix C).; In chapter 2, lily SCA-like molecules in Arabidopsis, AtLTP3 and AtLTP4, were also studied using RNA interference (RNAi). Introducing a RNAi construct for AtLTP4 into Arabidopsis plants resulted in decreased expression levels of both genes' expression due to their high sequence similarity. Anthers of the transgenic RNAi plants of iLTP4 were sterile and showed abnormal tapetum development. Aberrant pollen was also found inside the mature anther. Pistils of iLTP4 were semi-sterile when tested with the wild type pollen. Transgenic plants of iLTP4 also showed defects in vegetative growth, including the dwarf stature and rosette leaves that were narrower and less serrated than those of the wild type.; In summary, both extracelluar matrix (ECM) peptides, plantacyanin and AtLTP3/AtLTP4, are involved in pistil functions in Arabidopsis pollination; they may also have multiple roles in plant development, especially in male reproductive organs. |
