^ABSTRACT

Nitrogen is a main limiting nutrient for most plant species and other living organisms. Successful colonisation of plants by pathogens requires an efficient utilisation of nutrient resources present in host tissues; therefore, it is not surprising that hosts and pathogens have evolved distinct strategies to struggle for this essential element. Thus, phytopathogenic bacteria have developed specialised virulence factors (antimetabolite toxins) that inhibit the biosynthesis of certain amino acids, resulting in amino acid deficiencies in host cells and the accumulation of nitrogen-containing intermediates that can be assimilated by the pathogen. In addition, it is interesting to note that several bacterial and fungal genes specifically induced during pathogenesis are also expressed under nitrogen-limiting conditions in vitro, which suggests that the nitrogen status of the host may be one of the cues for pathogen gene expression and, in consequence, disease development. With regard to the plant, an important remobilisation of nitrogen takes place in infected tissues, which is most likely designed for the transfer of nitrogen from diseased to healthy tissues, where it might be used for plant defence and other host functions aimed at completing plant life cycle. Here we review recent literature on these little known, nitrogen related aspects of plant-pathogen interactions. Furthermore, the key role of nitrogen economy for plants and pathogens during bacterial and fungal pathogenesis will be discussed.