A -308 deletion of the tomato LAP promoters is able to direct flower-specific and MeJA-induced expression in transgenic plants

Identification and molecular evolution of the GLX genes in 21 plant species: a focus on the Gossypium hirsutum

BACKGROUND

The glyoxalase system includes glyoxalase I (GLXI), glyoxalase II (GLXII) and glyoxalase III (GLXIII), which are responsible for methylglyoxal (MG) detoxification and involved in abiotic stress responses such as drought, salinity and heavy metal.

RESULTS

In this study, a total of 620 GLX family genes were identified from 21 different plant species. The results of evolutionary analysis showed that GLX genes exist in all species from lower plants to higher plants, inferring that GLX genes might be important for plants, and GLXI and GLXII account for the majority. In addition, motif showed an expanding trend in the process of evolution. The analysis of cis-acting elements in 21 different plant species showed that the promoter region of the GLX genes were rich in phytohormones and biotic and abiotic stress-related elements, indicating that GLX genes can participate in a variety of life processes. In cotton, GLXs could be divided into two groups and most GLXIs distributed in group I, GLXIIs and GLXIIIs mainly belonged to group II, indicating that there are more similarities between GLXII and GLXIII in cotton evolution. The transcriptome data analysis and quantitative real-time PCR analysis (qRT-PCR) show that some members of GLX family would respond to high temperature treatment in G.hirsutum. The protein interaction network of GLXs in G.hirsutum implied that most members can participate in various life processes through protein interactions.

CONCLUSIONS

The results elucidated the evolutionary history of GLX family genes in plants and lay the foundation for their functions analysis in cotton.

Characterization and functional analysis of two novel 3-hydroxy-3-methylglutaryl-coenzyme A reductase genes (GbHMGR2 and GbHMGR3) from Ginkgo biloba

Terpene trilactones (TTLs) are the main secondary metabolites of Ginkgo biloba. As one of the rate-limiting enzymes in the mevalonic acid (MVA) pathway of TTL biosynthesis, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) catalyzes the 3-hydroxy-3-methylglutaryl coenzyme A to form MVA. In this study, two cDNA sequences of HMGR genes, namely, GbHMGR2 and GbHMGR3, were cloned from G. biloba. The protein sequences of GbHMGR2 and GbHMGR3, which contain several functional domains, were analyzed. Regulatory elements related to light, hormone, and stress response were detected in the promoter regions of GbHMGR2 and GbHMGR3. The catalytic activity of these genes was verified by a functional complement experiment in yeast. Quantitative real-time PCR (qRT-PCR) showed the distinct expression patterns of the two genes in different organs. The TTL contents in the organs were detected by high-performance liquid chromatography- evaporative light scattering detector. GbHMGR2 and GbHMGR3 were responded to cold, dark, methyl jasmonate (MJ), abscisic acid (ABA), salicylic acid (SA), and ethephon (Eth) treatments. The TTL contents were also regulated by cold, dark, MJ, ABA, SA, and Eth treatment. In conclusion, GbHMGR2 and GbHMGR3 may participate in the MVA pathway of TTL biosynthesis.

In silico identification and experimental validation of insertion-deletion polymorphisms in tomato genome

Comparative analysis of the genome sequences of Solanum lycopersicum variety Heinz 1706 and S. pimpinellifolium accession LA 1589 using MUGSY software identified 145 695 insertion-deletion (InDel) polymorphisms. A selected set of 3029 candidate InDels (≥2 bp) across the entire tomato genome were subjected to PCR validation, and 82.4% could be verified. Of 2272 polymorphic InDels between LA 1589 and Heinz 1706, 61.6, 45.2, and 31.6% were polymorphic in 8 accessions of S. pimpinellifolium, 4 accessions of S. lycopersicum var. cerasiforme, and 10 varieties of S. lycopersicum, respectively. Genetic distance was 0.216 in S. pimpinellifolium, 0.202 in S. lycopersicum var. cerasiforme, and 0.108 in S. lycopersicum. The data suggested a reduction of genetic variation from S. pimpinellifolium to S. lycopersicum var. cerasiforme and S. lycopersicum. Cluster analysis showed that the 8 accessions of S. pimpinellifolium were in one group, whereas 4 accessions of S. lycopersicum var. cerasiforme and 10 varieties of S. lycopersicum were in the same group.

Reproductive organ and vascular specific promoter of the rice plasma membrane Ca2+ATPase mediates environmental stress responses in plants

BACKGROUND

Plasma membrane Ca(2+)ATPase is a transport protein in the plasma membrane of cells and helps in removal of calcium (Ca(2+)) from the cell, hence regulating Ca(2+) level within cells. Though plant Ca(2+)ATPases have been shown to be involved in plant stress responses but their promoter regions have not been well studied.

RESULTS

The 1478 bp promoter sequence of rice plasma membrane Ca(2+)ATPase contains cis-acting elements responsive to stresses and plant hormones. To identify the functional region, serial deletions of the promoter were fused with the GUS sequence and four constructs were obtained. These were differentially activated under NaCl, PEG cold, methyl viologen, abscisic acid and methyl jasmonate treatments. We demonstrated that the rice plasma membrane Ca(2+)ATPase promoter is responsible for vascular-specific and multiple stress-inducible gene expression. Only full-length promoter showed specific GUS expression under stress conditions in floral parts. High GUS activity was observed in roots with all the promoter constructs. The -1478 to -886 bp flanking region responded well upon treatment with salt and drought. Only the full-length promoter presented cold-induced GUS expression in leaves, while in shoots slight expression was observed for -1210 and -886 bp flanking region. The -1210 bp deletion significantly responded to exogenous methyl viologen and abscisic acid induction. The -1210 and -886 bp flanking region resulted in increased GUS activity in leaves under methyl jasmonate treatments, whereas in shoots the -886 bp and -519 bp deletion gave higher expression. Salicylic acid failed to induce GUS activities in leaves for all the constructs.

CONCLUSIONS

The rice plasma membrane Ca(2+)ATPase promoter is a reproductive organ-specific as well as vascular-specific. This promoter contains drought, salt, cold, methyl viologen, abscisic acid and methyl jasmonate related cis-elements, which regulated gene expression. Overall, the tissue-specificity and inducible nature of this promoter could grant wide applicability in plant biotechnology.

Characterization of the tomato prosystemin promoter: organ-specific expression, hormone specificity and methyl jasmonate responsiveness by deletion analysis in transgenic tobacco plants

Tomato systemin is a bioactive peptide that regulates the systemic activation of wound-responsive genes. It is released from its 200 amino acid precursor called prosystemin. Initial tissue-localization and hormone-induced expression assays indicated that the tomato prosystemin gene (SlPS) accumulates mainly in floral tissues and in response to exogenous abscisic acid and methyl jasmonate (MeJA) treatments, respectively. Later, the promoter regions of the PS gene in tomato (Solanum lycopersicum L. cv. Castlemart), pepper (Capsicum annuum) and potato (Solanum tuberosum) were isolated and an in silico analysis of the SlPS promoter revealed an over-representation of stress- and MeJA-responsive motifs. A subsequent 5' deletion analysis of the SlPS promoter fused to the β-glucuronidase reporter (GUS) gene showed that the -221 to +40 bp proximal SlPS promoter region was sufficient to direct the stigma, vascular bundle-specific and MeJA-responsive expression of GUS in transgenic tobacco plants. Important vascular-tissue-specific, light- and MeJA-responsive cis-elements were also present in this region. These findings provide relevant information regarding the transcriptional regulation mechanisms of the SlPS promoter operating in transgenic tobacco plants. They also suggest that its tissue-specificity and inducible nature could have wide applicability in plant biotechnology.

Isolation and promoter analysis of a chalcone synthase gene PtrCHS4 from Populus trichocarpa

As perennial plants, Populus species are constantly exposed to environmental stresses, such as wounding and pathogen attack, which lead to production of compounds including lignin, flavonoids and phytoalexins. Chalcone synthase (CHS) is a key enzyme in the flavonoid biosynthesis pathway. In this study, a cDNA clone encoding CHS was isolated from Populus trichocarpa by reverse transcription-polymerase chain reaction (RT-PCR). The full-length cDNA, named PtrCHS4, was 1,314 bp with a 1,173 bp open reading frame that corresponded to a deduced protein of 391 amino acid residues. Multiple sequence alignments showed that PtrCHS4 shared high homology with CHS proteins from other plants. Phylogenetic analysis revealed that PtrCHS4 was most closely related to PhCHS from Petunia hybrida and NaCHS from Nicotiana attenuata. Semi-quantitative RT-PCR analysis identified that the PtrCHS4 gene was abundantly expressed in the leaves and stems, while its expression was drastically reduced in the roots. Transcript abundance of PtrCHS4 was stimulated by 2.5-fold within 24 h of wounding treatment. Promoter analysis confirmed that the PtrCHS4 promoter was capable of directing expression of the GUS reporter in both wounded and unwounded leaves of transgenic Chinese white poplar (P. tomentosa Carr.), indicating that the PtrCHS4 promoter is systemically responsive to wounding stimuli. Furthermore, promoter deletion analysis showed that the proximal 1,592 bp from the transcription start site were required for promoter activation by jasmonic acid and the -1,096 to -148 region was proved to be necessary for establishing wound-induced pattern of expression.

Induction of leucine aminopeptidase (LAP) like activity with wounding and methyl jasmonate in pigeonpea (Cajanas cajan) suggests the role of these enzymes in plant defense in leguminosae

Aminopeptidases are ubiquitous in nature and their activities have been identified in several plant species. Leucine aminopeptidases (LAPs) are predominantly studied in solanaceous plants and are induced in response to wounding, herbivory and methyl jasmonate (MeJA). The functions of plant aminopeptidases are still under discussion and it is likely that the different classes play various roles. In the present study we report the local and systemic induction of LAP-like activity upon mechanical wounding and MeJA treatment. Two proteins with LAP-like activity were detected in pigeonpea leaves. They were designated as AP1 and AP2. AP1 activity was significantly induced upon wounding and application of MeJA. The estimated molecular masses of AP1 and AP2 were ∼ 60 and 41 kDa respectively in SDS-PAGE. The pH optimum for LAP-like activity in control leaf extracts was found to be neutral (pH 7.0) however the enzymes showed highest activity at alkaline pH (pH 9.0) in the leaf extracts of treated plants. The temperature optimum for LAP-like activity was around 40-50 °C. The enzymes were strongly inhibited by 1, 10 phenanthroline and bestatin. Heavy metal ions and EDTA inhibited LAP-like activities, whereas Mn(+2) and Mg(+2) activated the enzyme activities. Beside LpNA (33.5 U/mg/min) pigeonpea LAP-like enzymes also cleaved ApNA (15 U/mg/min) but were unable to cleave VpNA. Total proteolytic activity was also observed to be induced in treated plants. LAP-like activity was increased upto 19.5 fold after gel filtration chromatography. Results suggest that these enzymes may have functional defensive role in pigeonpea.

A tomato bZIP transcription factor, SlAREB, is involved in water deficit and salt stress response

Abiotic stresses such as cold, water deficit, and salt stresses severely reduce crop productivity. Tomato (Solanum lycopersicum) is an important economic crop; however, not much is known about its stress responses. To gain insight into stress-responsive gene regulation in tomato plants, we identified transcription factors from a tomato cDNA microarray. An ABA-responsive element binding protein (AREB) was identified and named SlAREB. In tomato protoplasts, SlAREB transiently transactivated luciferase reporter gene expression driven by AtRD29A (responsive to dehydration) and SlLAP (leucine aminopeptidase) promoters with exogenous ABA application, which was suppressed by the kinase inhibitor staurosporine, indicating that an ABA-dependent post-translational modification is required for the transactivation ability of SlAREB protein. Electrophoretic mobility shift assays showed that the recombinant DNA-binding domain of SlAREB protein is able to bind AtRD29A and SlLAP promoter regions. Constitutively expressed SlAREB increased tolerance to water deficit and high salinity stresses in both Arabidopsis and tomato plants, which maintained PSII and membrane integrities as well as water content in plant bodies. Overproduction of SlAREB in Arabidopsis thaliana and tomato plants regulated stress-related genes AtRD29A, AtCOR47, and SlCI7-like dehydrin under ABA and abiotic stress treatments. Taken together, these results show that SlAREB functions to regulate some stress-responsive genes and that its overproduction improves plant tolerance to water deficit and salt stress.

Modification of tobacco plant development by sense and antisense expression of the tomato viroid-induced AGC VIIIa protein kinase PKV suggests involvement in gibberellin signaling

BACKGROUND

The serine-threonine protein kinase gene, designated pkv (protein kinase- viroid induced) was previously found to be transcriptionally activated in tomato plants infected with the plant pathogen Potato spindle tuber viroid (PSTVd). These plants exhibited symptoms of stunting, and abnormal development of leaf, root, and vascular tissues. The encoded protein, PKV, is a novel member of the AGC VIIIa group of signal-transducing protein kinases; however, the role of PKV in plant development is unknown. In this communication, we report the phenotypic results of over expression and silencing of pkv in transgenic tobacco.

RESULTS

Over expression of pkv in Nicotiana tabacum cv. Xanthi (tobacco) resulted in stunting, reduced root formation, and delay in flowering, phenotypes similar to symptoms of PSTVd infection of tomato. In addition, homozygous T2 tobacco plants over expressing PKV were male sterile. Antisense expression of pkv, on the other hand, resulted in plants that were taller than non-transformed plants, produced an increased number of flowers, and were fertile. Exogenous application of GA3 stimulated stem elongation in the stunted, sense-expressing plants. PKV sense and antisense expression altered transcript levels of GA biosynthetic genes and genes involved in developmental and signaling pathways, but not genes involved in salicylic acid- or jasmonic acid-dependent pathways. Our data provide evidence suggesting that PKV plays an important role in a GA signaling pathway that controls plant height and fertility.

CONCLUSION

We have found that the over expression of the tomato protein kinase PKV resulted in stunting, modified vascular tissue development, reduced root formation, and male sterility in tobacco, and we propose that PKV regulates plant development by functioning in critical signaling pathways involved in gibberellic acid metabolism.

Molecular cloning and characterization of the promoter for the multiple stress-inducible gene BjCHI1 from Brassica juncea

We have previously isolated a Brassica juncea cDNA encoding a novel chitinase BjCHI1 with two chitin-binding domains (Zhao and Chye in Plant Mol Biol 40:1009-1018, 1999). The expression of BjCHI1 was highly inducible by methyl jasmonate (MeJA) treatment, wounding, caterpillar feeding, and pathogenic fungal infection. These observations suggest that the promoter of BjCHI1 gene might contain specific cis-acting elements for stress responses. Here, we report the cloning and characterization of the BjCHI1 promoter. A 1,098 bp BjCHI1 genomic DNA fragment upstream of the ATG start codon was isolated by PCR walking and various constructs were made by fusing the BjCHI1 promoter or its derivatives to beta-glucuronidase reporter gene. The transgenic Arabidopsis plants showed that the BjCHI1 promoter responded to wounding and MeJA treatment, and to treatments with either NaCl or polyethyleneglycol (PEG 6000), indicating that the BjCHI1 promoter responses to both biotic and abiotic stresses. A transient gene expression system of Nicotiana benthamiana leaves was adopted for promoter deletion analysis, and the results showed that a 76 bp region from -695 to -620 in the BjCHI1 promoter was necessary for MeJA-responsive expression. Furthermore, removal of a conserved T/G-box (AACGTG) at -353 to -348 of the promoter greatly reduced the induction by MeJA. This is the first T/G-box element identified in a chitinase gene promoter. Gain-of-function analysis demonstrated that the cis-acting element present in the 76 bp region requires coupling with the T/G-box to confer full magnitude of BjCHI1 induction by MeJA.

Distinct repressing modules on the distal region of the SBP2 promoter contribute to its vascular tissue-specific expression in different vegetative organs

The Glycine max sucrose binding protein (GmSBP2) promoter directs vascular tissue-specific expression of reporter genes in transgenic tobacco. Here we showed that an SBP2-GFP fusion protein under the control of the GmSBP2 promoter accumulates in the vascular tissues of vegetative organs, which is consistent with the proposed involvement of SBP in sucrose transport-dependent physiological processes. Through gain-of-function experiments we confirmed that the tissue-specific determinants of the SBP2 promoter reside in the distal cis-regulatory domain A, CRD-A (position -2000 to -700) that is organized into a modular configuration to suppress promoter activity in tissues other than vascular tissues. The four analyzed CRD-A sub-modules, designates Frag II (-1785/-1508), Frag III (-1507/-1237), Frag IV (-1236/-971) and Frag V (-970/-700), act independently to alter the constitutive pattern of -92pSBP2-mediated GUS expression in different organs. Frag V fused to -92pSBP2-GUS restored the tissue-specific pattern of the full-length promoter in the shoot apex, but not in other organs. Likewise, Frag IV confined GUS expression to the vascular bundle of leaves, whereas Frag II mediated vascular specific expression in roots. Strong stem expression-repressing elements were located at positions -1485 to -1212, as Frag III limited GUS expression to the inner phloem. We have also mapped a procambium silencer to the consensus sequence CAGTTnCaAccACATTcCT which is located in both distal and proximal upstream modules. Fusion of either repressing element-containing module to the constitutive -92pSBP2 promoter suppresses GUS expression in the elongation zone of roots. Together our results demonstrate the unusual aspect of distal sequences negatively controlling tissue-specificity of a plant promoter.

Leucine aminopeptidases: diversity in structure and function

Leucine aminopeptidases (LAPs) are metallopeptidases that cleave N-terminal residues from proteins and peptides. While hydrolyzing Leu substrates, LAPs often have a broader specificity. LAPs are members of the M1 or M17 peptidase families, and therefore the LAP nomenclature is complex. LAPs are often viewed as cell maintenance enzymes with critical roles in turnover of peptides. In mammals, the M17 and M1 enzymes with LAP activity contribute to processing peptides for MHC I antigen presentation, processing of bioactive peptides (oxytocin, vasopressin, enkephalins), and vesicle trafficking to the plasma membrane. In microbes, the M17 LAPs have a role in proteolysis and have also acquired the ability to bind DNA. This property enables LAPs to serve as transcriptional repressors to control pyrimidine, alginate and cholera toxin biosynthesis, as well as mediate site-specific recombination events in plasmids and phages. In plants the roles of the M17 LAPs and the peptidases related to M1 LAPs are being elucidated. Roles in defense, membrane transport of auxin receptors, and meiosis have been implicated.

Pathogen-induced production of the antifungal AFP protein from Aspergillus giganteus confers resistance to the blast fungus Magnaporthe grisea in transgenic rice

Rice blast, caused by Magnaporthe grisea, is the most important fungal disease of cultivated rice worldwide. We have developed a strategy for creating disease resistance to M. grisea whereby pathogen-induced expression of the afp (antifungal protein) gene from Aspergillus giganteus occurs in transgenic rice plants. Here, we evaluated the activity of the promoters from three maize pathogenesis-related (PR) genes, ZmPR4, mpi, and PRms, in transgenic rice. Chimeric gene fusions were prepared between the maize promoters and the beta-glucuronidase reporter gene (gus A). Histochemical assays of GUS activity in transgenic rice revealed that the ZmPR4 promoter is strongly induced in response to fungal infection, treatment with fungal elicitors, and mechanical wounding. The ZmPR4 promoter is not active in the seed endosperm. The mpi promoter also proved responsiveness to fungal infection and wounding but not to treatment with elicitors. In contrast, no activity of the PRms promoter in leaves of transgenic rice was observed. Transgenic plants expressing the afp gene under the control of the ZmPR4 promoter were generated. Transformants showed resistance to M. grisea at various levels. Our results suggest that pathogen-inducible expression of the afp gene in rice plants may be a practical way for protection against the blast fungus. Most agricultural crop species suffer from a vast array of fungal diseases that cause severe yield losses all over the world. Rice blast, caused by the fungus Magnaporthe grisea (Herbert) Barr (anamorph Pyricularia grisea), is the most devastating disease of cultivated rice (Oryza sativa L.), due to its

Conserved MYC transcription factors play a key role in jasmonate signaling both in tomato and Arabidopsis

Jasmonates (JA) are important regulators of plant defense responses that activate expression of many wound-induced genes including the tomato proteinase inhibitor II (pin2) and leucine aminopeptidase (LAP) genes. Elements required for JA induction of the LAP gene are all present in the -317 to -78 proximal promoter region. Using yeast one-hybrid screening, we have identified the bHLH-leu zipper JAMYC2 and JAMYC10 proteins, specifically recognizing a T/G-box AACGTG motif in this promoter fragment. Mutation of the G-box element decreases JA-responsive LAP promoter expression. Expression of JAMYC2 and JAMYC10 is induced by JA, with a kinetics that precedes that of the LAP or pin2 transcripts. JAMYC overexpression enhanced JA-induced expression of these defense genes in potato, but did not result in constitutive transcript accumulation. Using footprinting assays, an additional protected element was identified, located directly adjacent to the T/G-box motif. Mutation of this element abolishes JA response, showing that recognition of this duplicated element is also required for gene expression. Knockout mutants in the AtMYC2 homolog gene of Arabidopsis are insensitive to JA and exhibit a decreased activation of the JA-responsive genes AtVSP and JR1. Activation of the PDF1.2 and b-CHI, ethylene/JA-responsive genes, is, however, increased in these mutants. These results show that the JAMYC/AtMYC2 transcription factors function as members of a MYC-based regulatory system conserved in dicotyledonous plants with a key role in JA-induced defense gene activation.

Identification of residues critical for activity of the wound-induced leucine aminopeptidase (LAP-A) of tomato

The importance of two putative Zn2+-binding (Asp347, Glu429) and two catalytic (Arg431, Lys354) residues in the tomato leucine aminopeptidase (LAP-A) function was tested. The impact of substitutions at these positions, corresponding to the bovine LAP residues Asp255, Glu334, Arg336, and Lys262, was evaluated in His6-LAP-A fusion proteins expressed in Escherichia coli. Sixty-five percent of the mutant His6-LAP-A proteins were unstable or had complete or partial defects in hexamer assembly or stability. The activity of hexameric His6-LAP-As on Xaa-Leu and Leu-Xaa dipeptides was tested. Most substitutions of Lys354 (a catalytic residue) resulted in His6-LAP-As that cleaved dipeptides at slower rates. The Glu429 mutants (a Zn2+-binding residue) had more diverse phenotypes. Some mutations abolished activity and others retained partial or complete activity. The E429D His6-LAP-A enzyme had Km and kcat values similar to the wild-type His6-LAP-A. One catalytic (Arg431) and one Zn-binding (Asp347) residue were essential for His6-LAP-A activity, as most R431 and D347 mutant His6-LAP-As did not hydrolyze dipeptides. The R431K His6-LAP-A that retained the positive charge had partial activity as reflected in the 4.8-fold decrease in kcat. Surprisingly, while the D347E mutant (that retained a negative charge at position 347) was inactive, the D347R mutant that introduced a positive charge retained partial activity. A model to explain these data is proposed.

The induction of tomato leucine aminopeptidase genes (LapA) after Pseudomonas syringae pv. tomato infection is primarily a wound response triggered by coronatine

Tomato plants constitutively express a neutral leucine aminopeptidase (LAP-N) and an acidic LAP (LAP-A) during floral development and in leaves in response to insect infestation, wounding, and Pseudomonas syringae pv. tomato infection. To assess the physiological roles of LAP-A, a LapA-antisense construct (35S:asLapA1) was introduced into tomato. The 35S:asLapA1 plants had greatly reduced or showed undetectable levels of LAP-A and LAP-N proteins in healthy and wounded leaves and during floral development. Despite the loss of these aminopeptidases, no global changes in protein profiles were noted. The 35S:asLapA1 plants also exhibited no significant alteration in floral development and did not impact the growth and development of Manduca sexta and P. syringae pv. tomato growth rates during compatible or incompatible infections. To investigate the mechanism underlying the strong induction of LapA upon P. syringae pv. tomato infection, LapA expression was monitored after infection with coronatine-producing and -deficient P. syringae pv. tomato strains. LapA RNA and activity were detected only with the coronatine-producing P. syringae pv. tomato strain. Coronatine treatment of excised shoots caused increases in RNAs for jasmonic acid (JA)-regulated wound-response genes (LapA and pin2) but did not influence expression of a JA-regulated pathogenesis-related protein gene (PR-1). These results indicated that coronatine mimicked the wound response but was insufficient to activate JA-regulated PR genes.

Overexpression, purification and biochemical characterization of the wound-induced leucine aminopeptidase of tomato

Wounding of tomato leaves results in the accumulation of an exoprotease called leucine aminopeptidase (LAP-A). While the expression of LapA genes are well characterized, the specificity of the LAP-A enzyme has not been studied. The LAP-A preprotein and mature polypeptide were overexpressed in Escherichia coli. PreLAP-A was not processed and was inactive accumulating in inclusion bodies. In contrast, 55-kDa mature LAP-A subunits assembled into an active, 357-kDa enzyme in E. coli. LAP-A from E. coli cultures was purified to apparent homogeneity and characterized relative to its animal (porcine LAP) and prokaryotic (E. coli PepA) homologues. Similar to the porcine and E. coli enzymes, the tomato LAP-A had high temperature and pH optima. Mn2+ was a strong activator for all three enzymes, while chelators, zinc ion, and the slow-binding aminopeptidase inhibitors (amastatin and bestatin) strongly inhibited activities of all three LAPs. The substrate specificities of porcine, E. coli and tomato LAPs were determined using amino-acid-p-nitroanilide and -beta-naphthylamide substrates. The tomato LAP-A preferentially hydrolyzed substrates with N-terminal Leu, Met and Arg residues. LAP-A had substantially lower levels of activity on other chromogenic substrates. Several differences in substrate specificities for the animal, plant and prokaryotic enzymes were noted.

Leucine aminopeptidase RNAs, proteins, and activities increase in response to water deficit, salinity, and the wound signals systemin, methyl jasmonate, and abscisic acid

LapA RNAs, proteins, and activities increased in response to systemin, methyl jasmonate, abscisic acid (ABA), ethylene, water deficit, and salinity in tomato (Lycopersicon esculentum). Salicylic acid inhibited wound-induced increases of LapA RNAs. Experiments using the ABA-deficient flacca mutant indicated that ABA was essential for wound and systemin induction of LapA, and ABA and systemin acted synergistically to induce LapA gene expression. In contrast, pin2 (proteinase inhibitor 2) was not dependent on exogenous ABA. Whereas both LapA and le4 (L. esculentum dehydrin) were up-regulated by increases in ABA, salinity, and water deficit, only LapA was regulated by octadecanoid pathway signals. Comparison of LapA expression with that of the PR-1 (pathogenesis-related 1) and GluB (basic beta-1,3-glucanase) genes indicated that these PR protein genes were modulated by a systemin-independent jasmonic acid-signaling pathway. These studies showed that at least four signaling pathways were utilized during tomato wound and defense responses. Analysis of the expression of a LapA1:GUS gene in transgenic plants indicated that the LapA1 promoter was active during floral and fruit development and was used during vegetative growth only in response to wounding, Pseudomonas syringae pv tomato infection, or wound signals. This comprehensive understanding of the regulation of LapA genes indicated that this regulatory program is distinct from the wound-induced pin2, ABA-responsive le4, and PR protein genes.