systemin and Wounds-and-Injuries

Oligogalacturonide fragments that activate defensive genes in plant leaves heretofore have been thought to be generated only by pathogen-derived pectin-degrading enzymes, because polygalacturonase (PG) activity has not been reported in leaves. Here, we report that mRNAs encoding a PG catalytic subunit protein and its regulatory (beta-subunit) protein are expressed in tomato leaves in response to wounding, systemin, and oligosaccharide elicitors. Synthesis of the two subunits in response to wounding is systemic and is accompanied by an increase in PG activity in extracts from both wounded and unwounded leaves. The finding that PG subunit mRNAs and PG enzyme activity are induced by wounding indicates that herbivore attacks can produce endogenous oligogalacturonide elicitors that may be involved in the local and systemic activation of defense responses against both herbivores and pathogens.

Topics: Amino Acid Sequence; Enzyme Induction; Gene Expression Regulation, Plant; Kinetics; Macromolecular Substances; Molecular Sequence Data; Peptides; Plant Leaves; Plant Proteins; Polygalacturonase; RNA, Messenger; Sequence Alignment; Sequence Homology, Amino Acid; Solanum lycopersicum; Transcription, Genetic; Wounds and Injuries

In cultured cells of Lycopersicon peruvianum, the oligopeptide systemin which mediates systemic signalling in the tomato wound response is rapidly inactivated by proteolytic cleavage of the bond carboxy-terminal to Lys14. A systemin derivative in which this peptide bond had been modified by N-methylation was resistant to proteolytic inactivation. Systemin elicits a rapid, transient alkalinization of the growth medium in L. peruvianum cells. Consistent with its metabolic stability, the response elicited by the N-methylated peptide was found to be more sustained than that caused by systemin. In differentiated tomato plants, the stabilized peptide was found to be 3 times more active than systemin with respect to the induction of proteinase inhibitors I and II. This result indicates the possible physiological significance of the observed proteolytic degradation for systemin inactivation in planta. The activity of a protease capable of processing systemin carboxy-terminal of Lys14 was detected in tomato plasma membranes and may be responsible for the inactivation process. Two further peptides, N-methylated at the bonds carboxy-terminal of Gln3 and Arg10 had proteinase inhibitor inducing activities lower by a factor of 8 and 80, respectively, as compared to systemin. Correspondingly, the alkalinization response elicited by these two peptides in cultured cells was found to be more transient than the systemin response. The correlation between the duration of the alkalinization response and the proteinase inhibitor inducing activities of systemin analogues may be indicative of a casual relationship between ion fluxes and defense gene induction.

Topics: Amino Acid Sequence; Cells, Cultured; Endopeptidases; Lysine; Molecular Sequence Data; Oligopeptides; Peptide Fragments; Peptides; Protease Inhibitors; Signal Transduction; Solanaceae; Wounds and Injuries

We investigated the relationship between the expression of lipoxygenase (LOX) genes and the systemin-dependent wound response in tomato (Lycopersicon esculentum) leaves. A polymerase chain reaction-based approach was used to isolate two tomato Lox cDNAs, called TomLoxC and TomLoxD. Both TomLOXC and TomLOXD amino acid sequences possess an N-terminal extension of about 60 residues that were shown by in vitro uptake to function as transit peptides, targeting these proteins into the chloroplast. Within 30 to 50 min following wounding or systemin or methyl jasmonate treatments, the TomLoxD mRNA level increased and reached a maximum between 1 and 2 h. TomLoxC mRNA was not detectable in leaves and was not found following wounding, but it was found in ripening fruits, indicating that the two tomato Lox genes are regulated in different tissues by different processes. The results suggest that the TomLoxD gene is up-regulated in leaves in response to wounding and encodes a chloroplast LOX that may play a role as a component of the octadecanoid defense-signaling pathway.

Topics: Acetates; Amino Acid Sequence; Chloroplasts; Cyclopentanes; Enzyme Induction; Gene Expression Regulation, Plant; Genes, Plant; Kinetics; Lipoxygenase; Molecular Sequence Data; Oxylipins; Peptides; Plant Growth Regulators; Plant Proteins; RNA, Messenger; Sequence Alignment; Sequence Homology, Amino Acid; Solanum lycopersicum; Time Factors; Transcription, Genetic; Wounds and Injuries

Bestatin, an inhibitor of some aminopeptidases in plants and animals, is a powerful inducer of defense genes in tomato leaves; these genes are also induced by herbivore attacks, mechanical wounding, systemin, and methyl jasmonate. Unlike wounding and systemin, bestatin does not cause an increase in intracellular jasmonic acid concentrations, and inhibitors of the octadecanoid pathway do not inhibit induction by bestatin. Furthermore, defense genes were induced by bestatin in a mutant tomato line (JL-5) with a defect in the octadecanoid pathway. Bestatin therefore appears to be exerting its effects close to the level of transcriptional control of these genes, where it may be inhibiting a regulatory protease.

Topics: Aminopeptidases; Animals; Base Sequence; Gene Expression; Genes, Plant; Leucine; Molecular Sequence Data; Mutation; Oligonucleotide Probes; Peptide Biosynthesis; Peptides; Plant Leaves; Plant Proteins; Protease Inhibitors; Solanum lycopersicum; Transcription, Genetic; Wounds and Injuries