Leucine aminopeptidases: the ubiquity of LAP-N and the specificity of LAP-A

The wound-induced leucine aminopeptidase (EC 3.4.11.1) genes, LapA1 and Lap A2, from tomato (Lycopersicon esculentum Mill.) were isolated and character ized. The genes were organized in a tandem array with approximately 6 kb se parating their coding regions. Quantitation of LapA mRNA levels in conjunct ion with nuclear run-on experiments indicated that LapA genes were primaril y under transcriptional control after wounding and infection with Pseudomon as syringae pv. tomato. In contrast, actin genes were down-regulated after pathogen infection. The sequences of the LapA1 and LapA2 5'-flanking region s were determined and several potential regulatory motifs were identified. Ribonuclease protection studies revealed that LapA1 and LapA2 had short Is- bp 5'-untranslated regions (UTR), both genes were expressed after wounding, and LapA1 mRNAs were 3.3-fold more abundant than LapA2 transcripts. While the region surrounding LapA1 was conserved, the 3'-UTRs and 3'-flanking reg ions of LapA2 had diverged in two inbred tomato lines. The accumulation of LapA mRNAs and of LAP-A (acidic pi), LAP-N (neutral pi) and LAP-related pro teins were examined in two monocot and five dicot species. The LAP-N and 66 - and 77-kDa LAP-related proteins were detected in healthy and wounded leav es of all plants examined. The LAP-A proteins were only detected in nightsh ade and their accumulation was distinct from that observed in tomato.