Minisymposium 14: Reproductive development

Abs # 27005: LePRK signal transduction in pollination: dephosphorylation and protein complex dissociation by an unusual style component.

Presenter:	Muschietti, Jorge , prometeo@dna.uba.ar
Authors	Muschietti, Jorge  (A)   Wengier, Diego  (A)   Tang, Weihua  (B)   Kelley, Dior  (B)   McCormick, Sheila  (B)   Cabanas, Marķa  (A)   Salem, Tamara  (A)   Sanchez, Sabrina  (A)   de Paz Sierra, Pablo  (A)
Affiliations:	(A): INGEBI-University of Buenos Aires (B): PGEC, USDA/ARS-UC-Berkeley
Web Site:	http://proteus.dna.uba.ar/muschietti.htm

In compatible pollination, after pollen grains germinate on the stigma, pollen tubes traverse the extracellular matrix of the style on their way to the ovules. During that journey, receptors in the pollen tube might perceive biochemical diverse style signals, thereby triggering pollen cytoplasmic events that are required for tip growth. We characterized two pollen-specific receptor-like kinases, LePRK1 and LePRK2, from tomato (Lycopersicon esculentum). Their structure, immunolocalization pattern and the specific LePRK2-dephosphorylation by style extracts suggested that these kinases might transduce some signal coming from the style (Muschietti et al., Plant Cell 1998, 319-330). We showed that LePRK1 and LePRK2 can be co-immunoprecipitated from pollen or when expressed together in yeast. In yeast their association requires LePRK2 kinase activity. In pollen, both LePRK1 and LePRK2 are found in a high molecular weight complex that is dissociated when pollen is germinated in vitro in the presence of style extract. In yeast, the addition of style extracts also disrupts the interaction between LePRK1 and LePRK2. Fractionation of the style extract revealed that the disruption activity and the specific LePRK2-dephosphorylation activity are enriched in the 3-10 kDa fraction (Wengier et al., PNAS 2003, 6860-6865). In contrast to the typical manner of receptor kinase activation, we propose this style component transduces the signal to pollen tubes by triggering the specific dephosphorylation of LePRK2 followed by dissociation of the LePRK complex. The style component, according to size exclusion chromatography, has a molecular weight of 6 kDa, is also heat-stable and is partially sensitive to proteases. It is not retained by either anionic or cationic exchange chromatography but it is retained by a cellulose column. It is resistant to DTT and to acid treatment and can be inactivated only by alkali treatment. All these findings suggest this style component is unusual.