Abstract
Abstract Ectopic expression of defensins in plants correlates with their increased capacity to withstand abiotic and biotic stresses. This applies to Arabidopsis thaliana, where some of the seven members of the Plant Defensin 1 family (AtPDF1) are recognised to improve plant responses to necrotrophic pathogens and increase seedling tolerance to excess zinc (Zn). However, few studies have explored the effects of decreased endogenous defensin expression on these stress responses. Here, we carried out an extensive physiological and biochemical comparative characterisation of i) novel amiRNA lines silenced for the five most similar AtPDF1s, and ii) a double null mutant for the two most distant AtPDF1s. Silencing of five AtPDF1 genes 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, while the double mutant behaved similarly to the WT. These unexpected results challenge the current paradigm describing the role of PDFs in the plant response to stresses. Additional roles of plant endogenous defensins are discussed, which open new perspectives for their functions.