LePRK2 signal transduction in pollination: two phosphorylation motifs that show antagonistic effects on pollen tube length and signaling by an unusual style peptide

MUSCHIETTI, JORGE; WENGIER, DIEGO; SALEM, TAMARA; SOTO, GABRIELA; BARBERINI, LAURA; MCCORMICK, SHEILA AND MAZZELLA, AGUSTINA

St. Louis, Missouri

Congreso; 9th International Plant Molecular Biology Congress; 2009

International Society for Plant Molecular Biology, University of Missouri, USDA-Agriculture Research Service

Our lab is interested in understanding the molecular mechanisms that control pollen-pistil interaction in tomato and Arabidopsis. During compatible pollinations, 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 (Muschietti et al., The Plant Cell 1998, 319-330). 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 (Wengier et al., PNAS 2003, 6860-6865). We showed that LePRK2 is hyperphosphorylated in pollen membranes. We also characterized two putative phosphorylation motifs in the cytoplasmic juxtamembrane domain that have opposite effects in regulating pollen tube length. We also showed that in vitro phosphorylated LePRK2 is specifically dephosphorylated when incubated with style exudates. 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. Taken together, these findings suggest that LePRK2 may have a central role in pollen tube growth through activation from style ligands and regulation of its own phosphorylation status.