RALFs: peptide regulators of plant growth

Abstract

Peptide signaling regulates a variety of developmental processes and environmental responses in plants. For example, the peptide systemin induces the systemic defense response in tomato and defensins are small cysteine-rich proteins that are involved in the innate immune system of plants. The CLAVATA3 peptide regulates meristem size and the SCR peptide is the pollen self-incompatibility recognition factor in the Brassicaceae. LURE peptides produced by synergid cells attract pollen tubes to the embryo sac. RALFs are a recently discovered family of plant peptides that play a role in plant cell growth.

Figure 1

Amino acid alignment of RALFs used in functional studies. SlRALF Solanum lycopersicum vegetative SGN-U316452; PtdRALF1 Hybrid Populus AY172330; NaRALF Nicotiana attenuata root AY456269.1; AtRALF1 Arabidopsis thaliana NM_100171; AtRALF23 Arabidopsis thaliana NM_112530; MtRALF Medicago truncatula MtC90970; SacRALF1 Saccharum spp CA182793.1; SlPRALF Solanum lycopersicum pollen SGN-U324197. SGN unigene sequences can be found at http://solgenomics.net/index.pl, and Medicago unigene sequences can be found at http://compbio.dfci.harvard.edu/tgi/cgi-bin/tgi/gimain.pl?gudb=medicago. All other gene annotations refer to GenBank accession numbers. Signal peptides shown are as predicted by TargetP (www.cbs.dtu.dk/services/TargetP/). Pro Peptides begin after the predicted signal cleavage site and end with dibasic processing site (arrow). Identical residues are boxed in black, and similar residues are shaded in gray. Consensus sequence of the predicted mature peptide indicates conservation in at least 6 out of 8 sequences. Asterisks indicate conserved cysteine residues.