Abstract
Agrobacterium tumefaciens can genetically transform various eukaryotic cells because of the presence of a resident tumor-inducing (Ti) plasmid. During infection, a defined region of the Ti plasmid, transfer DNA (T-DNA), is transferred from bacteria into plant cells and causes plant cells to abnormally synthesize auxin and cytokinin, which results in crown gall disease. T-DNA and several virulence (Vir) proteins are secreted through a type IV secretion system (T4SS) composed of T-pilus and a transmembrane protein complex. Three members of Arabidopsis reticulon-like B (RTNLB) proteins, RTNLB1, 2, and 4, interact with VirB2, the major component of T-pilus. Here, we have identified that other RTNLB proteins, RTNLB3 and 8, interact with VirB2 in vitro. Root-based A. tumefaciens transformation assays with Arabidopsis rtnlb3, or rtnlb5-10 single mutants showed that the rtnlb8 mutant was resistant to A. tumefaciens infection. In addition, rtnlb3 and rtnlb8 mutants showed reduced transient transformation efficiency in seedlings. RTNLB3- or 8 overexpression transgenic plants showed increased susceptibility to A. tumefaciens and Pseudomonas syringae infection. RTNLB1-4 and 8 transcript levels differed in roots, rosette leaves, cauline leaves, inflorescence, flowers, and siliques of wild-type plants. Taken together, RTNLB3 and 8 may participate in A. tumefaciens infection but may have different roles in plants.
Highlights
In nature, the phytopathogenic bacterium Agrobacterium tumefaciens of the family Rhizobiaceae infects susceptible plants and causes crown gall tumors
From the phylogenetic tree results of the Arabidopsis reticulon-like B (RTNLB) family, reticulon-like protein B1 (RTNLB1)-8 proteins belong to the Group I proteins containing an N-terminal domain with 43–93 amino acid residues and a short C-terminal domain [27,30]
We cloned RTNLB3 and RTNLB5-8 from Arabidopsis cDNA and examined whether RTNLB3 and RTNLB5-8 could interact with A. tumefaciens VirB2 bait protein in yeast two-hybrid assays
Summary
The phytopathogenic bacterium Agrobacterium tumefaciens of the family Rhizobiaceae infects susceptible plants and causes crown gall tumors. T-DNA transfer from A. tumefaciens into a plant cell requires the expression of several virulence (vir) genes that reside on the Ti plasmid [1,2,3,4]. The uncontrolled growth of crown gall tumors results from the transfer and expression of oncogenes encoded by the wild-type T-DNA, which directs overproduction of the plant growth hormones cytokinin and auxin [5] Another set of genes in wild-type T-DNA causes the production of bacterial nutrients, called opines, which are utilized by A. tumefaciens as a carbon and sometimes nitrogen source. Successful A. tumefaciens-mediated plant transformation involves a continuous battle of plant cells activating a defense response to repel bacterial infection and bacteria using Vir proteins and manipulating plant proteins to elude the plant’s immunity systems. This study further reveals the involvement of RTNLB3 and 8 in plant–microbe interactions
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