Pollen-Specific RALF from Tomato That Regulates Pollen Tube Elongation

• Published in: Plant physiology (Bethesda) 2010-06, Vol.153 (2), p.703-715
• Main Authors: Covey, Paul A, Subbaiah, Chalivendra C, Parsons, Ronald L, Pearce, Gregory, Lay, Fung T, Anderson, Marilyn A, Ryan, Clarence A, Bedinger, Patricia A
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino acids; Biological and medical sciences; Cell culture techniques; DEVELOPMENT AND HORMONE ACTION; Developmental biology; Fundamental and applied biological sciences. Psychology; Gene expression regulation; Gene Expression Regulation, Developmental; Gene Expression Regulation, Plant; Germination; Molecular Sequence Data; Peptide Hormones - genetics; Peptide Hormones - metabolism; Plant growth regulators; Plant physiology and development; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Pollen; Pollen Tube - growth & development; Pollen tubes; Protein Precursors - genetics; Protein Precursors - metabolism; RNA, Plant - genetics; Root growth; Sequence Alignment; Sexual reproduction; Solanum lycopersicum - genetics; Solanum lycopersicum - metabolism; Two-Hybrid System Techniques; Vegetative and sexual reproduction, floral biology, fructification
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.110.155457

Rapid Alkalinization Factors (RALFs) are plant peptides that rapidly increase the pH of plant suspension cell culture medium and inhibit root growth. A pollen-specific tomato (Solanum lycopersicum) RALF (SlPRALF) has been identified. The SlPRALF gene encodes a preproprotein that appears to be processed and released from the pollen tube as an active peptide. A synthetic SlPRALF peptide based on the putative active peptide did not affect pollen hydration or viability but inhibited the elongation of normal pollen tubes in an in vitro growth system. Inhibitory effects of SlPRALF were detectable at concentrations as low as 10 nM, and complete inhibition was observed at 1 μM peptide. At least 10-fold higher levels of alkSlPRALF, which lacks disulfide bonds, were required to see similar effects. A greater effect of peptide was observed in low-pH-buffered medium. Inhibition of pollen tube elongation was reversible if peptide was removed within 15 min of exposure. Addition of 100 nM SlPRALF to actively growing pollen tubes inhibited further elongation until tubes were 40 to 60 μm in length, after which pollen tubes became resistant to the peptide. The onset of resistance correlated with the timing of the exit of the male germ unit from the pollen grain into the tube. Thus, exogenous SlPRALF acts as a negative regulator of pollen tube elongation within a specific developmental window.