LePRK2 signal transduction in pollination: hyperphosphorylation and signaling by an unusual style peptide

MUSCHIETTI, JORGE; WENGIER, DIEGO; SALEM, TAMARA; MAZZELLA, AGUSTINA; BARBERINI, MARÍA LAURA; TANG, WEIHUA; MCCORMICK, SHEILA

Brasília-DF, Brasil

Congreso; XXth International Congress on Sexual Plant Reproduction; 2008

nternational Association of Sexual Plant Reproduction Research – IASPRR

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 mature pollen. Their immunolocalization pattern and the specific LePRK2-dephosphorylation by style extract suggested that at least LePRK2 transduces style signals (Muschietti et al., The Plant Cell 1998, 319-330). We showed 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 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). We also demonstrated that LePRK2 is hyperphosphorylated in pollen membranes where some of the phosphorylated residues are important for pollen tube growth. Using a combination of different chromatography systems we purified that style component to homogeneity; it is an extremely stable peptide with a molecular weight of 3,550 Da that stimulates pollen tube growth through LePRK2. All these findings suggest this style peptide is a key element of pollen-pistil signaling mediated by LePRK2.