Over-expression of virulence inhibiting peptides in Nicotiana tabacum plants as a tool to control Pseudomonas syringae pv. tabaci

The use of antimicrobial peptides (AMPs) to control phytopathogenic bacteria and fungi has been suggested as a potential alternative to conventional pesticides and antibiotics (Montesinos, 2007). Transgenic plants expressing AMPs could represent a good strategy to fight pathogens in both animal and plant hosts, although some concern still exist about several their intrinsic drawbacks (Keymanesh et al., 2009). Conversely, the design and use of innovative oligopeptides targeting Type Three Secretion System (T3SS) of Pseudomonas savastanoi pv. nerii has been previously showed to inhibit the development of the disease in its host Nerium oleander, without any toxic impact on plants (Cerboneschi et al., 2012). In this work, we describe the stable transformation and expression in Nicotiana tabacum plants of two of these short peptides, 17 and 27 aminoacids long, named AP17 and LI27, respectively. The transformation of Tobacco plants was performed using Agrobacterium EHA105, carrying the pCambia 1305.2gus binary vector, containing AP17 or LI27 sequences downstream the signal peptide GRP to target peptide delivery to apoplast (Biancalani et al., 2014). Transgenic lines were scored for antibiotic resistance on Linsmaier and Skoog medium containing 50 mg/l hygromycin, and then for AP17 or Li27 expression. Transgenic lines expressing high levels of each peptide were selected, and then in vitro inoculated with P. syringae pv tabaci ATCC 11528 (Pstab). While control untrans-formed plants were severely affected by Pstab infection, AP17 and Li27 transgenic plants showed faint or no symptoms, and the bacterial growth was severely impaired to reach zero level in few days after inoculation. This data demonstrated that constitutively expressed virulence inhibiting peptides could represent a promising strategy to control bacterial diseases of plants. Prelimary experiments are ongoing about the stable transformation and expression of Actinidia chinensis with peptides targeting T3SS of Pseudomonas syringae pv. actinidiae.