MUTATIONS IN TWO PUTATIVE PHOSPHORYLATION MOTIFS IN LePRK2 SHOW ANTAGONISTIC EFFECTS ON TUBE LENGTH

SALEM, TAMARA; MAZZELLA, AGUSTINA; WENGIER, DIEGO; MOTILLO, VIVIANA; PARISI, GUSTAVO; SALEM, TAMARA; MUSCHIETTI, JORGE

Tucuman

Congreso; XLV Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2009

The tip-growing pollen tube is a useful model for studyingpolarized cell growth in plants. We previously characterizedLePRK2, a pollen-specific receptor-like kinase from tomato(Solanum lycopersicum). When transiently overexpressed intobacco pollen tubes, LePRK2-eGFP significantly decreasedpollen tube length and increased pollen tube tip width, relative toeGFP tubes. Tubes that expressed a mutation in a lysine essential forkinase activity showed the same length and width as the eGFPcontrol. LePRK2 is present as multiple phosphorylated isoforms inmature pollen membranes. Using comparative sequence analysisand phosphorylation site prediction programs we identified twoputative phosphorylation motifs in the cytoplasmic juxtamembranedomain. Site-directed mutagenesis in these motifs, andoverexpression in tobacco pollen, showed that both motifs haveopposite effects in regulating pollen tube length. Relative toLePRK2-eGFP pollen tubes, alanine substitutions in residues ofmotif I, S277/S279/S282, resulted in longer pollen tubes, butalanine substitutions in motif II, S304/S307/T308, resulted inshorter tubes. We conclude that pollen tube length can be negativelyand positively regulated by phosphorylation of residues in motif Iand II respectively. These results suggest that LePRK2 may have arole in pollen tube growth through regulation of its ownphosphorylation status