Glycoside Hydrolase Genes Are Required for Virulence of Agrobacterium tumefaciens on Bryophyllum daigremontiana and Tomato.

Agrobacterium tumefaciens is a rhizosphere bacterium that can infect wound sites on plants. The bacterium transfers a segment of DNA (T-DNA) from the Ti plasmid to the plant host cell via a type IV secretion system where the DNA becomes integrated into the host cell chromosomes. The expression of T-DNA in the plant results in tumor formation. Although the binding of the bacteria to plant surfaces has been studied previously, there is little work on possible interactions of the bacteria with the plant cell wall. Seven of the 48 genes encoding putative glycoside hydrolases (Atu2295, Atu2371, Atu3104, Atu3129, Atu4560, Atu4561, and Atu4665) in the genome of A. tumefaciens C58 were found to play a role in virulence on tomato and Bryophyllum daigremontiana. Two of these genes (pglA and pglB; Atu3129 and Atu4560) encode enzymes capable of digesting polygalacturonic acid and, thus, may play a role in the digestion of pectin. One gene (arfA; Atu3104) encodes an arabinosylfuranosidase, which could remove arabinose from the ends of polysaccharide chains. Two genes (bglA and bglB; Atu2295 and Atu4561) encode proteins with beta-glycosidase activity and could digest a variety of plant cell wall oligosaccharides and polysaccharides. One gene (xynA; Atu2371) encodes a putative xylanase, which may play a role in the digestion of xylan. Another gene (melA; Atu4665) encodes a protein with alpha-galactosidase activity and may be involved in the breakdown of arabinogalactans. Limited digestion of the plant cell wall by A. tumefaciens may be involved in tumor formation on tomato and B. daigremontiana. IMPORTANCE A. tumefaciens is used in the construction of genetically engineered plants, as it is able to transfer DNA to plant hosts. Knowledge of the mechanisms of DNA transfer and the genes required will aid in the understanding of this process. Manipulation of glycoside hydrolases may increase transformation and widen the host range of the bacterium. A. tumefaciens also causes disease (crown gall tumors) on a variety of plants, including stone fruit trees, grapes, and grafted ornamentals such as roses. It is possible that compounds that inhibit glycoside hydrolases could be used to control crown gall disease caused by A. tumefaciens.