Characterization of response regulator GacA involved in phaseolotoxin production, hypersensitive response and cellular processes in Pseudomonas syringae pv. actinidiae A18

Pseudomonas syringae pv. actinidiae is the phytopathogen responsible for kiwifruit canker, one of the most important kiwifruit bacterial diseases worldwide. In this work, two phaseolotoxin-related genes (gacA and glmS) were cloned and identified through transposon mutagenesis in conjunction with Escherichia coli toxin bioassay, which resulted in completely abolishment in the production of phaseolotoxin in P. syringae pv. actinidiae A18. Further study showed that motility ability, exopolysaccharides production and biofilm formation were reduced in the gacA-defective mutant. Moreover, a diminished hypersensitive response in tobacco was observed with the gacA-defective mutant when compared to wild-type strain after infiltration. Our experimental results represented a first view that GacA might play a key role in controlling phaseolotoxin biosynthesis, hypersensitive response and cellular processes in this bacterium.