PMID:24443526

Citation	Barnhart, DM, Su, S and Farrand, SK (2014) A signaling pathway involving the diguanylate cyclase CelR and the response regulator DivK controls cellulose synthesis in Agrobacterium tumefaciens. J. Bacteriol. 196:1257-74
Abstract	The production of cellulose fibrils is involved in the attachment of Agrobacterium tumefaciens to its plant host. Consistent with previous studies, we reported recently that a putative diguanylate cyclase, celR, is required for synthesis of this polymer in A. tumefaciens. In this study, the effects of celR and other components of the regulatory pathway of cellulose production were explored. Mutational analysis of celR demonstrated that the cyclase requires the catalytic GGEEF motif, as well as the conserved aspartate residue of a CheY-like receiver domain, for stimulating cellulose production. Moreover, a site-directed mutation within the PilZ domain of CelA, the catalytic subunit of the cellulose synthase complex, greatly reduced cellulose production. In addition, deletion of divK, the first gene of the divK-celR operon, also reduced cellulose production. This requirement for divK was alleviated by expression of a constitutively active form of CelR, suggesting that DivK acts upstream of CelR activation. Based on bacterial two-hybrid assays, CelR homodimerizes but does not interact with DivK. The mutation in divK additionally affected cell morphology, and this effect was complementable by a wild-type copy of the gene, but not by the constitutively active allele of celR. These results support the hypothesis that CelR is a bona fide c-di-GMP synthase and that the nucleotide signal produced by this enzyme activates CelA via the PilZ domain. Our studies also suggest that the DivK/CelR signaling pathway in Agrobacterium regulates cellulose production independent of cell cycle checkpoint systems that are controlled by divK.
Links	PubMed PMC3957726 Online version:10.1128/JB.01446-13
Keywords	Agrobacterium tumefaciens/cytology; Agrobacterium tumefaciens/genetics; Agrobacterium tumefaciens/metabolism; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Cell Cycle; Cellulose/biosynthesis; DNA Mutational Analysis; Gene Deletion; Gene Expression Regulation, Bacterial; Genetic Complementation Test; Mutagenesis, Site-Directed; Protein Multimerization; Repressor Proteins/genetics; Repressor Proteins/metabolism; Signal Transduction; Transcription Factors/genetics; Transcription Factors/metabolism; Two-Hybrid System Techniques
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
AGRFC:Q7CZK0	Contributes to	GO:0000160: phosphorelay signal transduction system	ECO:0000269:		P		DivK plays a role in the pathway for activation of CelR. This result suggests that it is the absence of celR in the divK-celR deletion mutant that is responsible for most, of this decrease in levels of cellulose.	complete

References

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