Chemocyanin, a small basic protein from the lily stigma, induces pollen tube chemotropism

doi:10.1073/pnas.2533800100

Chemocyanin, a small basic protein from the lily stigma, induces pollen tube chemotropism

^*Center for Plant Cell Biology, Department of Botany and Plant Sciences, and ^§Mass Spectrometry Facility, Department of Chemistry, University of California, Riverside, CA 92521

Edited by June B. Nasrallah, Cornell University, Ithaca, NY (received for review June 19, 2003)

Abstract

In plant reproduction, pollination is an essential process that delivers the sperm through specialized extracellular matrices (ECM) of the pistil to the ovule. Although specific mechanisms of guidance for pollen tubes through the pistil are not known, the female tissues play a critical role in this event. Many studies have documented the existence of diffusible chemotropic factors in the lily stigma that can induce pollen tube chemotropism in vitro, but no molecules have been isolated to date. In this study, we identified a chemotropic compound from the stigma by use of biochemical methods. We purified a lily stigma protein that is active in an in vitro chemotropism assay by using cation exchange, gel filtration, and HPLC. Tryptic digestion of the protein yielded peptides that identified the protein as a plantacyanin (basic blue protein), and this was confirmed by cloning the cDNA from the lily stigma. Plantacyanins are small cell wall proteins of unknown function. The measured molecular mass by electrospray ionization ion source MS is 9,898 Da, and the molecular mass of the mature protein (calculated from the cDNA) is 9,900.2 Da. Activity of the lily plantacyanin (named chemocyanin) is enhanced in the presence of stigma/stylar cysteine-rich adhesin, previously identified as a pollen tube adhesin in the lily style.

Footnotes

↵ ¶ To whom correspondence should be addressed. E-mail: lord{at}citrus.ucr.edu.
↵ † S.K. and J.-C.M. contributed equally to this work.
↵ ‡ Present address: Laboratoire de Glycobiologie et Physiologie Végétale, Faculté Jean Perrin, Université d'Artois, SP 18, Rue Souvraz, 62307 Lens Cedex, France.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: ECM, extracellular matrix; GM, growth medium; SP, stigma protein; SCA, stigma/stylar cysteine-rich adhesin; ESI, electrospray ionization.
Data deposition: The sequences reported in this paper have been deposited in the GenBank and Swiss-Prot databases [accession nos.: GenBank AY425323 (lily chemocyanin), Swiss-Prot Q94GZ1 (rice plantacyanin), Swiss-Prot Q8LG89 (Arabidopsis plantacyanin), and Swiss-Prot P00303 (cucumber plantacyanin)].