| Phytohormone networks are used to regulate the plant response to virulent bacterial pathogens. In this work by the use of salicylic acid (SA) deficient lines it is shown that SA, a major player in the interaction between Arabidopsis and virulent Pseudomonas syringae pv. tomato (Pst), down-regulates ethylene and jasmonates. SA influences ethylene production in an NPR1-independent manner and jasmonate production in an NPR1-dependent manner. Pst-produced coronatine, a jasmonate mimic, acts independently of SA and does not compromise SA-dependent basal resistance. These three phytohormones are also involved in the response of tomato to Xanthomonas campestris pv. vesicatoria (Xcv). However, the hormone network is dramatically different to that of Arabidopsis. It is demonstrated, by the use of phytohormone deficient plants and pathogenesis-related marker gene expression profiling, that a systemic signal is generated in tomato in response to an infection with virulent Xcv. This signal is SA-dependent and leads to the development of a systemic acquired tolerance in tomato to subsequent infections with virulent Xcv. This systemic acquired tolerance is similar to the systemic response that is generated in response to avirulent Xcv. |
