SIGNALING STUDIES IN THE EMERGING KIWIFRUIT PATHOGEN Pseudomonas syringae pv. actinidiae

摘要

In the past two decades emerging and re-emerging plant pathogens have caused new threats to theproduction of several economically important crops, one among them is P. syringae pv. actinidiae(PSA) which causes canker or leaf spot on kiwifruit plants. PSA enters plant through wounds andremains dormant in cortex tissue of the branches, and spreads in the tissue to cause severesymptoms from winter to early spring. The disease can be visualized by brown discoloration ofbuds, dark brown angular spots surrounded by yellow haloes on leaves, cankers with white toreddish (oxydation) exudate on twigs and trunks, fruit collapse, wilting and eventually plantmortality. Current control methods have their own significance in disease control, however thereis considerable lack of clear understanding of PSA pathogenicity. Virulence of plant pathogensoften relies on the synchronized/coordinated expression of pathogenicity factors via quorumsensing (QS). Therefore, investigations on QS in PSA may lead to develop novel disease controlstrategies and reliable methods to curb the disease. It is currently unknown whether PSA producesa QS signal molecule thus the aim of this thesis is to investigate whether PSA possesses a QSsystem. As genome mining did not reveal the presence of any currently known QS system, thisstudy initially by metabolomics was aimed at identifying potentially low molecular weightsecondary metabolite QS molecules produced by PSA. Azelaic acid was discovered to be producedby PSA, this is the first report of azelaic acid production by bacteria. The characterization andpossible role of azelaic acid in QS is presented. Since azelaic acid is ubiquitous in nature, inaddition to determining its biological role, the catabolism of azelaic acid in bacteria using theefficient degrader Pseudomonas nitroreducens DSM 9128 was also studied.