Design and synthesis of strong root gravitropism inhibitors with no concomitant growth inhibition.

Herein, we describe a highly potent gravitropic bending inhibitor with no concomitant growth inhibition. Previously, we reported that (2Z,4E)-5-phenylpenta-2,4-dienoic acid (ku-76) selectively inhibits root gravitropic bending of lettuce radicles at 5 µM. Based on the structure-activity relationship study of ku-76 as a lead compound, we designed and synthesized various C4-substituted analogs of ku-76. Among the analogs, 4-phenylethynyl analog exhibited the highest potency for gravitropic bending inhibition, which was effective at only 0.01 µM. Remarkably, 4-phenylethynyl analog is much more potent than the known inhibitor, NPA. Substitution in the para position on the aromatic ring of 4-phenylethynyl group was tolerated without diminished activity. In addition, evaluation using Arabidopsis indicated that 4-phenylethynyl analog inhibits gravitropism by affecting auxin distribution in the root tips. Based on the effects on Arabidopsis phenotypes, 4-phenylethynyl analog may be a novel inhibitor that differs in action from the previously reported auxin transport inhibitors.

Expression of a gene for an MLX56 defense protein derived from mulberry latex confers strong resistance against a broad range of insect pests on transgenic tomato lines.

Insect pests cause serious damage in crop production, and various attempts have been made to produce insect-resistant crops, including the expression of genes for proteins with anti-herbivory activity, such as Bt (Bacillus thuringiensis) toxins. However, the number of available genes with sufficient anti-herbivory activity is limited. MLX56 is an anti-herbivory protein isolated from the latex of mulberry plants, and has been shown to have strong growth-suppressing activity against the larvae of a variety of lepidopteran species. As a model of herbivore-resistant plants, we produced transgenic tomato lines expressing the gene for MLX56. The transgenic tomato lines showed strong anti-herbivory activities against the larvae of the common cutworm, Spodoptera litura. Surprisingly, the transgenic tomato lines also exhibited strong activity against the attack of western flower thrips, Frankliniera occidentalis. Further, growth of the hadda beetle, Henosepilachna vigintioctopunctata, fed on leaves of transgenic tomato was significantly retarded. The levels of damage caused by both western flower thrips and hadda beetles were negligible in the high-MLX56-expressing tomato line. These results indicate that introduction of the gene for MLX56 into crops can enhance crop resistance against a wide range of pest insects, and that MLX56 can be utilized in developing genetically modified (GM) pest-resistant crops.

Design and chemical synthesis of root gravitropism inhibitors: Bridged analogues of ku-76 have more potent activity.

Previously, we found (2Z,4E)-5-phenylpenta-2,4-dienoic acid (ku-76) to be a selective inhibitor of root gravitropic bending of lettuce radicles at 5 µM, with no concomitant growth inhibition, and revealed the structure-activity relationship in this inhibitory activity. The conformation of ku-76 is flexible owing to the open-chain structure of pentan-2,4-dienoic acid with freely rotating single bonds, and the (2Z)-alkene moiety may be isomerized by external factors. To develop more potent inhibitors and obtain insight into the target biomolecules, various analogues of ku-76, fixed through conformation and/or configuration, were synthesized and evaluated. Stereochemical fixation was effective in improving the potency of gravitropic bending inhibition. Finally, we found highly potent conformational and/or configurational analogues (ku-257, ku-294 and ku-308), that did not inhibit root growth. The inhibition of root curvature by these analogues was comparable to that of naptalam.

Essential structural features of (2Z,4E)-5-phenylpenta-2,4-dienoic acid for inhibition of root gravitropism.

Previously, we found (2Z,4E)-5-phenylpenta-2,4-dienoic acid (ku-76) to be a selective inhibitor of root gravitropic bending of lettuce radicles at 5 µM, with no concomitant growth inhibition. Here, we describe a structure-activity relationship study of ku-76 to determine the essential structural features for the inhibitory activity. A series of ku-76 analogues was synthesized and the key features of ku-76 that are necessary for inhibition of lettuce root gravitropic bending were determined. The (2E,4E)-, (2Z,4Z)- (2E,4Z)- analogues were inactive, and 4,5-saturated and 4,5-alkynyl analogues also did not show inhibitory activity, demonstrating the importance of the (2Z,4E) diene unit. The aromatic ring was also crucial and could not be replaced with an alkyl chain. Derivatives in which the carboxylic acid was replaced with amides, alcohols, or esters were much less potent. These results suggest that the (2Z,4E)-diene, the carboxylic acid moiety, and the aromatic ring are essential for potent inhibitory activity against gravitropic bending.

Transcriptomic evaluation of plant growth inhibitory activity of goniothalamin from the Malaysian medicinal plant Goniothalamus andersonii.

Goniothalamin produced by the Malaysian medicinal plant, Goniothalamus andersonii J. Sinclair, strongly inhibits plant growth. However, its mode of action has not been characterized at the gene expression level. We conducted DNA microarray assay to analyze the changes in early gene responses of Arabidopsis thaliana seedlings. After a 6-h exposure to goniothalamin, we observed an upregulation of genes highly associated with heat response, and 22 heat shock protein (AtHSP) genes were upregulated more than 50 fold. Together with these genes, we observed upregulation of the genes related to oxidative stress and protein folding. Also, the genes related to cell wall modification and cell growth, expansin (AtEXPA) genes, were significantly downregulated. The results suggested that goniothalamin induces oxidative stresses and inhibits the expression of cell wall-associated proteins resulting in growth inhibition of Arabidopsis seedlings.

Plant growth inhibitor from the Malaysian medicinal plant Goniothalamus andersonii and related species.

A crude methanol extract of Goniothalamus andersonii J. Sinclair strongly inhibited elongation of lettuce (Lactuca sativa L.) radicles. We conducted bioassay-guided purification of G. andersonii bark extract and obtained goniothalamin as the major bioactive compound. Its EC50 values against elongation of lettuce radicles and hypocotyls were 50 and 125 micromol L(-1), respectively. Among the six species tested, timothy was the most sensitive to goniothalamin. Quantification of this compound in other Goniothalamus species suggested that the plant inhibitory activity of this genus is explainable by goniothalamin, with G. calcareus as an exception.

Quantification of cyanamide in young seedlings of Vicia species, Lens culinaris, and Robinia pseudo-acacia by gas chromatography-mass spectrometry.

We quantified the cyanamide content of young leaves of nine Vicia species, Lens culinaris, and Robinia pseudo-acacia using a modified analytical procedure that made it possible to measure the cyanamide content of a single leaf. Recent molecular phylogenetic analysis suggests that cyanamide is present in V. benghalensis, which is placed in a monophyletic group with cyanamide-biosynthesizing plants, V. villosa and V. cracca; this suggestion was verified.

A unique latex protein, MLX56, defends mulberry trees from insects.

The mulberry (Morus spp.)-silkworm (Bombyx mori) relationship has been a well-known plant-herbivore interaction for thousands of years. Recently, we found that mulberry leaves defend against insect herbivory by latex ingredients. Here we report that a 56-kDa (394 amino acid) defense protein in mulberry latex designated mulatexin (MLX56) with an extensin domain, two hevein-like chitin-binding domains, and an inactive chitinase-like domain provides mulberry trees with strong insect resistance. MLX56 is toxic to lepidopteran caterpillars, including the cabbage armyworm, Mamestra brassicae and the Eri silkworm, Samia ricini, at 0.01% concentration in a wet diet, suggesting that MLX56 is applicable for plant protection. MLX56 is highly resistant to protease digestion, and has a strong chitin-binding activity. Interestingly, MLX56 showed no toxicity to B. mori, suggesting that the mulberry specialist has developed adaptation to the mulberry defense. Our results show that defensive proteins in plant latex play key roles in mulberry-insect interactions, and probably also in other plant-insect interactions. Our results further suggest that plant latexes analogous to animal venom contain a treasury of applicable defense proteins and chemicals that has evolved through inter-specific interactions.

Differential effects of sugar-mimic alkaloids in mulberry latex on sugar metabolism and disaccharidases of Eri and domesticated silkworms: enzymatic adaptation of Bombyx mori to mulberry defense.

Mulberry leaves (Morus spp.) exude latex rich in sugar-mimic alkaloids, 1,4-dideoxy-1,4-imino-d-arabinitol (d-AB1) and 1-deoxynojirimycin (DNJ), as a defense against herbivorous insects. Sugar-mimic alkaloids are inhibitors of sugar-metabolizing enzymes, and are toxic to the Eri silkworm, Samia ricini, a generalist herbivore, but not at all to the domesticated silkworm, Bombyx mori, a mulberry specialist. To address the phenomena, we fed both larvae diets containing different sugar sources (sucrose, glucose or none) with or without sugar-mimic alkaloids from mulberry latex. In S. ricini, addition of sugar-mimic alkaloids to the sucrose (the major sugar in mulberry leaves) diet reduced both growth and the absorption ratio of sugar, but it reduced neither in B. mori. The midgut soluble sucrase activity of S. ricini was low and inhibited by very low concentrations of sugar-mimic alkaloids (IC(50)=0.9-8.2microM), but that of B. mori was high and not inhibited even by very high concentrations (IC(50)>1000microM) of sugar-mimic alkaloids. In S. ricini, the addition of sugar-mimic alkaloids to the glucose diet still had considerable negative effects on growth, although it did not reduce the absorption ratio of glucose. The hemolymph of S. ricini fed sugar-mimic alkaloids contained sugar-mimic alkaloids. The trehalose concentration in the hemolymph increased significantly in S. ricini fed sugar-mimic alkaloids, but not in B. mori. The trehalase activities of S. ricini were lower and inhibited by lower concentrations of sugar-mimic alkaloids than those of B. mori. These results suggest that sugar-mimic alkaloids in mulberry latex exert toxicity to S. ricini larvae first by inhibiting midgut sucrase and digestion of sucrose, and secondly, after being absorbed into hemolymph, by inhibiting trehalase and utilization of trehalose, the major blood sugar. Further, our results reveal that B. mori larvae evolved enzymatic adaptation to mulberry defense by developing sucrase and trehalase that are insensitive to sugar-mimic alkaloids.

Efficient solubilization, activation, and purification of recombinant Cry45Aa of Bacillus thuringiensis expressed as inclusion bodies in Escherichia coli.

A cytotoxic protein Cry45Aa of Bacillus thuringiensis expressed as inclusion bodies in Escherichia coli was solubilized in 10 mM HCl. Protein concentration of saturated solution of the recombinant Cry45Aa in 10 mM HCl was about 25 times higher than that in the buffer of previous method (in 50 mM sodium carbonate buffer, pH 10.5, containing 1 mM EDTA, and 10 mM dithiothreitol). The Cry45Aa solubilized in the acidic solution was activated by pepsin as an alternative to proteinase K in the previous method. Cytotoxic activity against CACO-2 cells of the pepsin-treated Cry45Aa was almost identical to the proteinase K-treated protein. The pepsin-treated Cry45Aa was purified by cation-exchange chromatography. The concentration of the purified protein was 539 microg/ml, which was 27-fold higher than that of the activated Cry45Aa by the previously method. The cytotoxic activity of the purified protein was stable in broad pH region (pH 2.0-11.0) for 3 days, and 97% cytotoxic activity remained after incubation at 30 degrees C for 360 min.

Cloning and characterization of a novel gene cry9Ec1 encoding lepidopteran-specific parasporal inclusion protein from a Bacillus thuringiensis serovar galleriae strain.

A novel delta-endotoxin gene from a lepidopteran-specific Bacillus thuringiensis serovar galleriae strain was cloned, and the full sequence of the cry gene was determined. The cloned 6.5-kb DNA fragment included the full sequence of the cry gene and three open reading frames located upstream of the cry gene. The gene, designated cry9Ec1, encodes a polypeptide of 1154 amino acid residues with a predicted molecular weight of 130 237. The deduced amino acid sequence of the Cry9Ec1 protein had the highest homology (77.7%) with the Cry9Ea1 protein when compared with existing Cry proteins. The expression, in an acrystalliferous B. thuringiensis strain, of the cry9Ec1 gene was high when controlled by the cyt1A2 promoter, leading to the formation of large spherical inclusions. The purified crystals from the recombinant strain were toxic when tested against two lepidopteran species, Bombyx mori and Plutella xylostella. However, the Cry9Ec1 protein gave no toxicity against Spodoptera litura, Spodoptera exigua, Plodia interpunctella, Helicoverpa zea, and Culex pipiens molestus.

Cloning and characterization of two novel genes, cry24B and s1orf2, from a mosquitocidal strain of Bacillus thuringiensis serovar sotto.

Two new crystal protein genes, cry24B and s1orf2, were cloned from a mosquitocidal Bacillus thuringiensis serovar sotto strain. The cry24B and s1orf2 genes encoded a 76-kDa and 62-kDa protein, respectively. The Cry24B protein retained five conserved regions commonly found in the existing Cry proteins. The amino acid sequence of the S1ORF2 had a high homology to that of the ORF2 protein of B. thuringiensis serovar jegathesan. Southern hybridization experiments with a cry24B gene-specific probe revealed that these genes are located on two large plasmids of > 100 kb. When the two genes, cry24B and s1orf2, were expressed in an acrystalliferous B. thuringiensis host, the proteins were synthesized and accumulated as inclusions. These inclusions exhibited no larvicidal activities against three mosquito species: Aedes aegypti, Anopheles stephensi, and Culex pipiens molestus. Likewise, the inclusions contained no cytocidal activity against HeLa cells.

Identification of a novel cytotoxic protein, Cry45Aa, from Bacillus thuringiensis A1470 and its selective cytotoxic activity against various mammalian cell lines.

Parasporal inclusion proteins produced by Bacillus thuringiensis strain A1470 exhibit strong cytotoxicity against human leukemic T cells when activated by protease treatment. One of the cytotoxic proteins was separated by anion exchange chromatography and gel filtration chromatography and designated Cry45Aa. Its gene was then expressed in recombinant Escherichia coli, in which the Cry45Aa precursor was accumulated in an inclusion body. It was solubilized in sodium carbonate buffer and processed with proteinase K, and cytotoxic activities of the protein against various mammalian cell lines were evaluated using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide assay. The protein exhibited high cytotoxic activity against CACO-2, Sawano, MOLT-4, TCS, and HL60 cells and moderate activity against U-937 DE-4, PC12, and HepG2 cells. On the other hand, the EC50 values against Jurkat, K562, HeLa, A549, Vero, COS-7, NIH3T3, CHO, and four normal tissue cells (human primary hepatocyte cells, UtSMC, MRC-5, and normal T cells) were >2 microg/mL.

A new insertion variant, IS231I, isolated from a mosquito-specific strain of Bacillus thuringiensis.

A new insertion variant belonging to the family IS231, designated IS231I, was isolated from a mosquito larvicidal strain of the Bacillus thuringiensis serovar sotto (H4ab). IS231I was 1653 bp long and delimited by two 20 bp inverted repeats with one mismatch, flanked by two perfect 11 bp direct repeats. The element contained a single open reading frame (ORF) encoding 478 amino acids and five conserved domains: N1, N2, N3, C1, and C2. The 5' noncoding region upstream of the ORF, presumed to form a stable stem-and-loop structure, was highly conserved in IS231I. The secondary structure conformation had a deduced free energy (DeltaG=25 degrees C) of -17.2 kcal/mol. Comparison of the IS231I amino acid sequence with those of the 10 existing IS variants revealed that the new variant shares 89% identity with IS231A and IS231B, 65-66% with IS231M and IS231N, and 38% with IS231W.

Characterization of flagellar antigens and insecticidal activities of Bacillus thuringiensis populations in animal feces.

In total, 287 Bacillus thuringiensis isolates, recovered from feces of 28 zoo-maintained animal species, were examined for flagellar (H) antigenicity and insecticidal activity. Serologically, 209 isolates (72.8%) were allocated to the 8 H serogroups, 4 were untypable, and 74 were untestable. Among the 8 H serotypes detected, H3abc (serovar kurstaki) predominated at a high frequency of 88.0%, followed by H6 (serovar entomocidus) with a frequency of 7.7%. Insecticidal activity was associated with 67.2% of the fecal populations: 188 isolates were toxic to both Bombyx mori (Lepidoptera: Bombycidae) and Aedes aegypti (Diptera: Culicidae), 2 isolates were specific for B. mori, and 3 isolates were toxic to A. aegypti only. Of the isolates with dual toxicity, 97.9% belonged to the serovar kurstaki, producing bipyramidal parasporal inclusions. All of the H7 (serovar aizawai) isolates were toxic to both insects.

Mannose-specific lectin activity of parasporal proteins from a lepidoptera-specific Bacillus thuringiensis strain.

Lectin activity, agglutinating sheep erythrocytes, was associated with parasporal inclusion proteins from a Lepidoptera-specific isolate of Bacillus thuringiensis serovar galleriae (H5ab). The activity was generated when parasporal inclusions were solubilized in an alkaline condition. Proteolytic processing was not required for generation of the lectin activity; the activity level was not affected by the presence/absence of the three proteases (trypsin, chymotrypsin, and proteinase K). SDS-PAGE analysis revealed that (1) alkali-solubilized parasporal inclusion proteins consisted of two major components of 130 kDa and 65 kDa, and (2) proteinase K treatment of alkali-solubilized proteins yielded a single major protein of 60 kDa. Lectin activity of our isolate was strongly inhibited by preincubation with D-mannose, but not with the six other monosaccharides: D-galactose, D-glucose, L-fucose, N-acetyl- D-glucosamine, N-acetyl- D-galactosamine, and N-acetylneuraminic acid. In contrast, D-mannose did not inhibit the in vivo larvicidal activity of the proteins against the silkworm, Bombyx mori.

Extremely high frequency of common flagellar antigens between Bacillus thuringiensis and Bacillus cereus.

Bacillus cereus isolates, recovered from natural environments of Japan, were examined for their flagellar (H) antigenicities with the reference H antisera against Bacillus thuringiensis serotypes H1-H55. Of 236 B. cereus isolates tested, 165 (70%) were agglutinated with the reference antisera available. The frequencies of seropositive isolates were: 77% in soils, 68% on phylloplanes, and 60% in animal fecal populations. Among the 45 H serogroups detected, the serovar shandongiensis (H22) was the predominant, followed by the serovars entomocidus (H6), indiana (H16), pakistani (H13), and neoleonensis (H24ab). These five H serovars were commonly distributed in the three populations from different sources.