| The wound response in plants is triggered by tissue damage incurred from biotic and abiotic sources. However, identification of wound-specific genes has been complicated by overlap between the wound response and other stress responses. Using representational difference analysis (RDA), an anthocyanidin synthase (ANS), steroid sulfotransferase (SST) and a tyramine transferase (THT) were isolated from wounded Arabidopsis thaliana. These genes were expressed in wounded leaves and corresponding systemic tissues. Analysis in wild-type and mutant backgrounds showed that their wound induction was entirely dependent upon jasmonate signaling. SST and putative paralog At5g07000 possess sequence hallmarks of steroid sulfotransferases. The expression of SST was silenced using RNAi. A silenced (SST::RNAi) line was analyzed for differences in steroid profiles between unwounded and wounded plants. However, differences were not detected between wild-type and SST::RNAi plants. Possible reasons for this result are discussed. An RDA-based screen for wounding genes expressed solely in systemic tissues (SYSTs) revealed, instead, genes whose expression is down-regulated in injured leaves. SYST1-3 was depleted in wounded leaves within five minutes after wounding and maintained at reduced levels for at least four days. Genetic approaches failed to identify the signal involved in SYST1-3 reduction. A SYST1-3-like gene, At5g16250, was isolated by homology search and was similarly depleted in wounded leaves indicating a gene family of wound-depleted transcripts. To gain insight into the wound response of a lower eukaryotic plant, the wound response was investigated in the moss, Physcomitrella patens. Wounding caused cell death to 1-2 cell layers bordering the wound. Callose was deposited in cells adjacent to the wounded cells. Two putative lipoxygenases (PpLOX) were induced by wounding. PpLOX6 and PpLOX7 contain features of lipoxygenases from higher plants. PpLOX7 is predicted to be transported into the chloroplast and a dendrogram showed that PpLOX7 is related to the wound-induced type2-lipoxygenases whereas PpLOX6 clustered with the moss lipoxygenases. Induction of PpLOX7 could be triggered by methyl jasmonate. Wounding also induced putative orthologs of JA biosynthetic enzymes, allene oxide synthase (AOS) and allene oxide cyclase (AOC) but not an OPDA reductase ( OPR3). These results suggest that a JA-dependent wound response may be conserved in mosses. |
