Abstract
Ectopic expression of defensins in plants correlates with their increased capacity to withstand abiotic and biotic stresses(Carvalho & Gomes, 2011). However, few studies have explored the effects of decreased plant endogenous defensin transcripts on these stress responses.When over-expressed in Arabidopsis thaliana, some of the seven members of thePlant Defensin type 1 family (PDF1) are recognised to improve plant responses tonecrotrophic pathogens(De Conincket al.,2010)and increase seedling tolerance to excess zinc (Zn;Mirouzeet al., 2006). We carried out an extensive physiological and biochemical comparative characterisation of i) novel transgenic amiRNA lines silenced for the five most similarAtPDF1s, and ii) a double null mutant for the two most distant AtPDF1s. Silencing of fiveAtPDF1transcripts was specifically associated with increased aboveground dry mass production in mature plants under Zn excess conditions, and with increased plant tolerance to different pathogens–one fungus, one oomycete and one bacterium.These unexpected results challenge the current paradigm describing the role ofPDFs in the plant response to stresses.Additional roles of plant defensins are discussed, which open onto new perspectives for their functions(Nguyen et al., submitted).