Symposium III: Advances in plant reproductive biology

Abs # 30002: Chemocyanin, a peptide from the lily stigma, induces pollen tube guidance

Presenter:	Lord, Elizabeth M., Lord@citrus.ucr.edu
Authors	Lord, Elizabeth M. (A)   Dong, Juan  (A)
Affiliations:	(A): Center for Plant Cell Biology,Department of Botany and Plant Sciences, University of California, Riverside CA. 92521
Web Site:	http://www.cepceb.ucr.edu

In flowering plants, where the sperm cells are carried in a unique transport system ,the pollen tube, and the egg is sequestered deep inside the tissues of the pistil, there are numerous opportunities for signaling including guidance. Strong evidence points toward the existence of chemotropic molecules in the pistil that act in guiding pollen tubes to their destination in the ovary. These molecules are in the pistil ECMs and many will be acting on the pollen tube tip where the dynamic machinery for both growth and cell movement exist. Discovery of the native factors in the pistil ECMs that act to guide pollen tubes will enable us to better understand the signaling network in the tube cell, much as the yeast mating factors have enabled the field of signal transduction to progress. We have recently discovered two peptides (SCA and chemocyanin) from the lily pistil ECM that act in pollen tube guidance, the first such chemotropic peptides found in plants (Kim et al 2003).Chemocyanin is a plantacyanin in the phytocyanin ( blue copper protein ) family. Our proposal is that on the lily stigma a gradient of chemocyanin acts to guide pollen tubes into the style. In some unknown way SCA potentiates the chemotropic activity of chemocyanin. Once the pollen tubes are in the style, a SCA/pectin adhesive matrix acts to track them to the ovary.This we propose is an adhesion driven guidance ,without gradients of chemo attractants involved.Expressed lily chemocyanin protein is active in the chemotropism assay. Arabidopsis has a single plantacyanin gene with 67% similarity to chemocyanin.This plantacyanin was recently shown to be induced by low temperature. We have identified the transcripts of this gene in Arabidopsis leaves, inflorescences, roots and stems by RT-PCR, with the highest level in the inflorescence. Transgenic Arabidopsis plants with the plantacyanin promoter region fused with the GUS gene show expression in the stigma. A knockdown mutant was obtained, but no visible phenotypes were found under normal growth conditions. Recombinant Arabidopsis plantacyanin is active in the in vitro chemotropism assay with lily pollen tubes. References: Kim S, Mollet JC, Dong J, Zhang K, Park SY, Lord EM (2003) Chemocyanin, a small basic protein from the lily stigma, induces pollen tube chemotropism. Proc Natl Acad Sci U S A. 100(26): 16125-30.