| Summary: | <i>Agrobacterium tumefaciens</i> uses the type IV secretion system, which consists of VirB1-B11 and VirD4 proteins, to deliver effectors into plant cells. The effectors manipulate plant proteins to assist in T-DNA transfer, integration, and expression in plant cells. The <i>Arabidopsis</i> reticulon-like (RTNLB) proteins are located in the endoplasmic reticulum and are involved in endomembrane trafficking in plant cells. The <i>rtnlb4</i> mutants were recalcitrant to <i>A. tumefaciens</i> infection, but overexpression of <i>RTNLB4</i> in transgenic plants resulted in hypersusceptibility to <i>A. tumefaciens</i> transformation, which suggests the involvement of RTNLB4 in <i>A. tumefaciens</i> infection. The expression of defense-related genes, including <i>FRK1</i>, <i>PR1</i>, <i>WRKY22</i>, and <i>WRKY29</i>, were less induced in <i>RTNLB4</i> overexpression (O/E) transgenic plants after <i>A. tumefaciens</i> elf18 peptide treatment. Pretreatment with elf18 peptide decreased <i>Agrobacterium</i>-mediated transient expression efficiency more in wild-type seedlings than <i>RTNLB4</i> O/E transgenic plants, which suggests that the induced defense responses in <i>RTNLB4</i> O/E transgenic plants might be affected after bacterial elicitor treatments. Similarly, <i>A. tumefaciens</i> VirB2 peptide pretreatment reduced transient T-DNA expression in wild-type seedlings to a greater extent than in <i>RTNLB4</i> O/E transgenic seedlings. Furthermore, the VirB2 peptides induced <i>FRK1</i>, <i>WRKY22</i>, and <i>WRKY29</i> gene expression in wild-type seedlings but not <i>efr-1</i> and <i>bak1</i> mutants. The induced defense-related gene expression was lower in <i>RTNLB4</i> O/E transgenic plants than wild-type seedlings after VirB2 peptide treatment. These data suggest that RTNLB4 may participate in elf18 and VirB2 peptide-induced defense responses and may therefore affect the <i>A. tumefaciens</i> infection process.
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