Two types of
necrosis-inducing lipodepsipeptide toxins, called
syringomycin and syringopeptin, are major
virulence factors of Pseudomonas syringae pv. syringae strain B301D. A previous study showed that a locus, called syrA, was required for both
syringomycin production and plant pathogenicity, and the syrA locus was speculated to encode a regulator of toxin production. In this study, sequence analysis of the 8-kb genomic
DNA fragment that complements the syrA phenotype revealed high conservation among a broad spectrum of fluorescent pseudomonads. The putative
protein encoded by open reading frame 4 (ORF4) (1,299 bp) in the syrA locus region exhibited 85% identity to ArgA, which is involved in
arginine biosynthesis in Pseudomonas aeruginosa. Growth of strain W4S2545, the syrA mutant, required supplementation of N minimal medium with
arginine. Similarly,
syringomycin production of syrA mutant W4S2545 was restored by the addition of
arginine to
culture media. Furthermore, the insertion of Tn5 in the genome of the syrA mutant W4S2545 was localized between
nucleotides 146 and 147 in ORF4, and
syringomycin production was complemented in trans with the wild-type
DNA fragment containing intact ORF4. These results demonstrate that the syrA locus is the argA gene of P. syringae pv. syringae and that argA is directly involved in
arginine biosynthesis and therefore indirectly affects
syringomycin production because of
arginine deficiency.