The Ectopic Expression of CaRop1 Modulates the Response of Tobacco Plants to Ralstonia solanacearum and Aphids.

In plants, Rho related GTPases (Rops) are versatile molecular switches that regulate various biological processes, although their exact roles are not fully understood. Herein, we provide evidence that the ectopic expression of a Rop derived from Capsicum annuum, designated CaRopl, in tobacco plants modulates the response of these plants to Ralstonia solanacearum or aphid attack. The deduced amino acid sequence of CaRopl harbors a conserved Rho domain and is highly homologous to Rops of other plant species. Transient expression of a CaRopl-GFP fusion protein in Nicotiana benthamiana leaf epidermal cells revealed localization of the GFP signal to the plasma membrane, cytoplasm, and nucleus. Overexpression (OE) of the wild-type CaRopl or its dominant-negative mutant (DN-CaRopl) conferred substantial resistance to R, solanacearum infection and aphid attack, and this effect was accompanied by enhanced transcriptional expression of the hypersensitive-reaction marker gene HSR201; the jasmonic acid (JA)-responsive PR1b and LOX1; the insect resistance associated NtPI-1, NtP1-11, and NtTPI; the ethylene (ET) production-associated NtACS1; and NPK1, a mitogen-activated protein kinase kinase kinase (MAPKKK) that interferes with N-, Bs2-, and Rx-mediated disease resistance. In contrast, OE of the constitutively active mutant of CaRopl (CA-CaRopl) enhanced susceptibility of the transgenic tobacco plants to R. solanacearum infection and aphid attack and downregulated or sustained the expression of HSR201, PR1b, NPK1, NtACS1, NtPI-1, NtPI-11, and NtTP1. These results collectively suggest that CaRopl acts as a signaling switch in the crosstalk between Solanaceaes's response to R. solanacearum infection and aphid attack possibly via JA/ET-mediated signaling machinery.