The orf13 T-DNA Gene of Agrobacterium rhizogenes Confers Meristematic Competence to Differentiated Cells

Abstract

Plant infections by the soil bacterium Agrobacterium rhizogenes result in neoplastic disease with the formation of hairy roots at the site of infection. Expression of a set of oncogenes residing on the stably integrated T-DNA is responsible for the disease symptoms. Besides the rol (root locus) genes, which are essential for the formation of hairy roots, the open reading frame orf13 mediates cytokinin-like effects, suggesting an interaction with hormone signaling pathways. Here we show that ORF13 induced ectopic expression of KNOX (KNOTTED1-like homeobox) class transcription factors, as well as of several genes involved in cell cycle control in tomato (Lycopersicon esculentum). ORF13 has a retinoblastoma (RB)-binding motif and interacted with maize (Zea mays) RB in vitro, whereas ORF13, bearing a point mutation in the RB-binding motif (ORF13*), did not. Increased cell divisions in the vegetative shoot apical meristem and accelerated formation of leaf primordia were observed in plants expressing orf13, whereas the expression of orf13* had no influence on cell division rates in the shoot apical meristem, suggesting a role of RB in the regulation of the cell cycle in meristematic tissues. On the other hand, ectopic expression of LeT6 was not dependent on a functional RB-binding motif. Hormone homeostasis was only altered in explants of leaves, whereas in the root no effects were observed. We suggest that ORF13 confers meristematic competence to cells infected by A. rhizogenes by inducing the expression of KNOX genes and promotes the transition of infected cells from the G1 to the S phase by binding to RB.

An Oncoprotein from the Plant PathogenAgrobacteriumHas Histone Chaperone–Like Activity

“…The predicted amino acid sequence of 6b is somewhat similar to those of a number of proteins encoded by other genes, such as rolB and ORF13 in Ri plasmids, which also cause aberrant growth and the abnormal morphology of both roots and shoots (Spena et al, 1987;Levesque et al, 1988;Stieger et al, 2004). The product of ORF13 has a retinoblastoma binding motif (LXCXE) and interacts with maize (Zea mays) Rb in vitro (Stieger et al, 2004).…”

“…The product of ORF13 has a retinoblastoma binding motif (LXCXE) and interacts with maize (Zea mays) Rb in vitro (Stieger et al, 2004). RolB, which includes a Tyr phosphatase motif (CX5R), has phosphatase activity (Filippini et al, 1996).…”

Agrobacterium rhizogenes-Mediated Transformation and Its Biotechnological Applications in Crops

“…The ORF13 and ORF14 genes are found to be highly conserved among A. rhizogenes strains (Stieger et al 2004). It has been demonstrated that alone A4-rolABC genes carried by an Agrobacterium strain are showed to be incapable of inducing rooting on carrot disc and aux genes located on the T R -DNA or ORF13 and ORF14 located on T L -DNA are also required for rooting (Cardarelli et al 1987b;Capone et al 1989).…”

“…Stieger et al (2004) claimed that a proliferative effect of ORF13 expression in the shoot apical meristem (SAM) caused increased number of mitoses and showed no influence on meristem structure. In consequence, the reductions of cell and meristem sizes and the retardation in the formation of leaf primordia were observed.…”

Molecular insights into plant cell proliferation disturbance by Agrobacterium protein 6b

“…The predicted amino acid sequence of 6b is distantly related to the RolB family proteins, whose expression also results in aberrant growth and abnormal morphology of both roots and shoots (Spena et al 1987;Levesque et al 1988;Stieger et al 2004). Protein 6b localizes to the nucleus and was reported to bind to several nuclear proteins-such as NtSIP1 (Nicotiana tabacum Six-b-interacting protein 1) (Kitakura et al 2002), NtSIP2 (Kitakura et al 2008), and histone H3 (Terakura et al 2007)-and affects the expression of various plant genes in transgenic Arabidopsis.…”