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

MUSCHIETTI, JORGE; WENGIER, DIEGO; MCCORMICK, SHEILA; SALEM, TAMARA

Holderness School, USA

Conferencia; Gordon Conference. Plant Molecular Biology July 16-21, 2006.; 2006

Gordon Research COnferences

In compatible pollination, after pollen grains germinate on the stigma, pollen tubes traverse the style on their way to the ovules. During that journey, pollen tube receptors might perceive style signals, thereby triggering cytoplasmic events required for tip growth. We characterized two pollen-specific receptor-like kinases, LePRK1 and LePRK2, from tomato. Their immunolocalization pattern and the specific LePRK2-dephosphorylation by style extracts suggested they might transduce style signals (Muschietti et al., The Plant Cell 1998, 319-330). We showed LePRK1 and LePRK2 can be co-immunoprecipitated from pollen or when expressed together in yeast. 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 extracts. In yeast, style extracts disrupt the interaction between LePRK1 and LePRK2. In contrast to the typical manner of receptor kinase activation, we propose this style component transduces the signal by triggering LePRK2 dephosphorylation followed by dissociation of the LePRK complex (Wengier et al., PNAS 2003, 6860-6865). Using a combination of different chromatography systems we purified this style component to homogeneity; according to Mass Spectrometry analysis it has a molecular weight of 3,550 Da, is heat-stable, resistant to acid hydrolysis and can be inactivated only by alkali treatment. All these findings suggest this style component is a key element of pollen-pistil signaling mediated by the LePRKs.