The virulence (vir) genes of Agrobacterium tumefaciens are induced by low-molecular-weight phenolic compounds and monosaccharides through a two-component regulatory system consisting of the VirA and VirG proteins. However, it is not clear how the phenolic compounds are sensed by the VirA/VirG system. We tested the vir-inducing abilities of 15 different phenolic compounds using four wildtype strains ofA. tumefaciens-KU12, C58, A6, and Bo542. We analyzed the relationship between structures of the phenolic compounds and levels of vir gene expression in these strains. In strain KU12, vir genes were not induced by phenolic compounds containing 4'-hydroxy, 3'-methoxy, and 5'-methoxy groups, such as acetosyringone, which strongly induced vir genes of the other three strains. On the other hand, vir genes of strain KU12 were induced by phenolic compounds containing only a 4'-hydroxy group, such as 4-hydroxyacetophenone, which did not induce vir genes of the other three strains. The vir genes of strains KU12, A6, and Bo542 were all induced by phenolic compounds containing 4'-hydroxy and 3'-methoxy groups, such as acetovanillone. By transferring different Ti plasmids into isogenic chromosomal backgrounds, we showed that the phenolic-sensing determinant is associated with Ti plasmid. Subcloning Table 2 show that the induction response to different phenolic compounds varies among the different strains.Under our standard induction conditions, vir genes in both the octopine-type strain A6 and the succinamopine-type strain Bo542 were strongly induced by all phenolic compounds in group A. The nopaline-type strain C58 showed a moderate level of vir gene induction by acetosyringone and sinapinic acid. However, no response to syringaldehyde, syringic acid, and 2,6-dimethoxyphenol was observed. Surprisingly, we found that all phenolic compounds in group A, including acetosyringone, the most commonly used vir gene inducer in the laboratory, were unable to induce the vir genes of strain KU12. All strains except C58 responded to acetovanillone and ferulic acid of group B, and strains KU12 and Bo542 were both induced by guaiacol. However, only strain Bo542 was induced by vanillin of group B. In our hands, strain A6 was not induced by vanillin, a phenolic compound classified as a strong vir gene inducer by Melchers et al. (29) using A. tumefaciens strain LBA2516, which contains an octopine-type Ti plasmid, pTiB6, that is closely related to pTiA6 (12). The reason for this discrepancy is not clear. Of special interest is the observation that the vir genes of strain KU12 were highly induced by a group of compounds in group C that lack both methoxy groups. These compounds included 4-hydroxyacetophenone, p-coumaric acid, and phenol, which had previously been reported to be non-vir gene inducers (29). In support of this latter report, the three otherA. tumefaciens strains were indeed not induced by the phenolic compounds in group C.We tested vir gene induction by other phenolic compounds that lacked the hydroxyl group at the R4 posi...

The formation of crown gall tumors by Agrobacterium tumefaciens requires that the virulence (vir) genes be induced by chemical signals which consist of specific phenolic compounds and monosaccharides, synthesized at plant wound sites. Signal transduction in the activation of these genes is mediated by the VirA-VirG twocomponent regulatory system, together with ChvE, a glucose-galactose binding protein which interacts with VirA. We have previously presented genetic evidence that virA senses phenolic compounds directly (Y.-W. Lee, S. Jin, W.-S. Sim, and E. W. Nester, Proc. Natl. Acad. Sci. USA 92:12245-12249, 1995). The vir genes of strain KU12 can be induced by 4-hydroxyacetophenone, p-coumaric acid, and phenol, whereas these same phenolic compounds are weak inducers of the vir genes of strain A6. In this report, we show that a specific inducing sugar can broaden the specificity of the phenolic compound which VirA senses. 4-Hydroxyacetophenone and other related phenolic compounds function as inducing phenolic compounds with the virA gene of A6 if arabinose replaces glucose as the inducing sugar. We further demonstrate that this broadened specificity for phenolic inducers results from the increased level of ChvE through induction by arabinose via the regulatory protein GbpR. If high levels of ChvE are present, then poorly inducing phenolic compounds can induce the vir genes to high levels in combination with glucose. Comparing the induction response of the wild type and that of a VirA mutant with a mutation in its receiver domain revealed that the activity of the receiver domain is controlled by the periplasmic domain. We discuss these observations in terms of how VirA senses and transduces signals elicited by the two classes of plant signal molecules.

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To use oil palm empty fruit bunch (EFB) for cellulase production, a novel fungus was isolated from moistened EFB. This fungus was classified as Penicillium sp. by sequence analysis of the internal transcribing space and it was named Penicillium sp. GDX01. The Penicillium sp. strain secreted cellulases under solid-state fermentation of EFB. The fermentation conditions were optimized for maximal enzyme production. Of the different substrates tested, both EFB and rice straw gave the maximum production of filter paper activity (FPase). Five percent yeast extract and 40-50% initial moisture content were found to be optimal for enzyme production. In addition, the pretreatment of EFB with NaOH before fermentation inhibited the cellulase production of Penicillium sp. GDX01. Saccharification of pretreated EFB by cellulases from Penicillium sp. GDX01 resulted in a more than 80% release of glucose during a 72 h incubation, which is a better result than when using Celluclast 1.5L without the addition of β-glucosidase. Our results show that the cellulases produced by Penicillium sp. GDX01 are more efficient at the saccharification of EFB than Celluclast 1.5 L.