Biosynthesis of gibberellin plant hormons by pathogenic bacteria

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Gibberellins are plant hormones that coordinate their precisely timed development. They are important for regulation of e.g. stem elongation, germination, dormancy, flowering, leaf senescence and fruit development. More recently it was also revealed that gibberellins can alter the induction of plant defense against herbivores and pathogens. For those reasons biosynthesis and the mode of action are well studied in plants and the plant pathogenic fungi Gibberella fujikuroi causing the bakanae disease, where infected rice plants grow too rapidly and often fall over. However besides pathogenic fungi, also pathogenic bacteria seem to be able to produce gibberellins. The presence of a gibberellin biosynthetic operon was recently confirmed in the rice pathogen Xanthomonas oryzae pv. oryzicola and the wheat/barley pathogens Xanthomonas translucens pv. translucens and pv. graminis. An analysis of the genes present in the biosynthetic operon shows that different genes are involved in the later steps of gibberellin biosynthesis in bacteria compared to plants or fungi, indicating that gibberellin biosynthesis may evolved separately three times. The proposed project aims to elucidate the underlying biochemical pathway for gibberellin biosynthesis in these Xanthomonas spp. in detail, as well as to characterize the relevance of gibberellins for plant-pathogen interaction.