Secretion of Zeatin, Ribosylzeatin, and Ribosyl-1″ -Methylzeatin by Pseudomonas savastanoi

Abstract

Cytokinin production by strains of the phytopathogenic bacterium Pseudomonas syningae pv savastanoi was measured by immunoaffinity chromatography of the culture medium on immobilized anti-cytokinin antibodies, followed by high performance liquid chromatography, radioimmunoassay and mass spectrometry. P. sawastanoi strain PB213-2 secretes zeatin (80 nanograms per milliliter) and ribosylzeatin (80 nanograms per milliliter). Even higher levels of zeatin (400 nanograms per milliliter) are produced by the olive-specific strain EW1006, which also produces 180 nanograms per milliliter of the recently identified cytokinin, ribosyl-l"-methylzeatin. The amounts secreted were approximately 1000 times greater than those secreted by Agrobacterium tumefaciens Biochem Biophys Res Commun 104: 1560-1566. Examination of cytokinin production by' plasmid deletion mutants of PB213-2 and EW1006 indicated that cytokinin biosynthesis was specified, at least in part, by plasmid-borne genes. A fragment of the 105 kilobase pair plasmid from EW1006 was cloned into Escherichia coli where its expression resulted in dimethylallyl transferase activity and the secretion of zeatin.Gall-forming phytopathogenic bacteria have long been known to produce plant hormones (11,28) and there has been speculation, supported by recent evidence, that pathogenesis may be hormone-dependent. It is now known that the bacterial pathogens Pseudomonas syringae pv savastanoi and Agrobacterium tumefaciens contain genes which specify the synthesis of IAA. P. savastanoi, the causative organism of olive and oleander knot, contains two plasmid-born genes which specify IAA biosynthesis (6,7, 17); the first, iaaM, encodes the enzyme tryptophan monooxygenase (12) while the second, iaaH, encodes an indoleacetamide hydrolase. Both genes are required for effective

Bacterial volatiles promote growth in Arabidopsis

“…Chromatographic profiles of volatiles from bacteria strains IN937a and GB03, both of which promote growth by the emission of volatile chemicals, compared with a growth-promoting strain that does not trigger promotion by volatile emissions 89B61, a nongrowth-promoting bacterial strain DH5␣, and an uninoculated medium control. Compounds positively identified include 3-hydroxy-2-butanone [1], 2,3-butanediol [2], decane [6], tetramethyl pyrazine [9], undecane [10], decanal [13], dodecane [14], 2-undecanone [16], 2-tridecanone [17], and 2-tridecanol [18]; nonyl acetate was added as an internal standard (IS). Asterisks in the lower chromatograms designate compounds that align with numbered peaks above.…”

Global Genomic Analysis of Pseudomonas savastanoi pv. savastanoi Plasmids

“…In fact, in most oleander isolates of P. savastanoi, the genes responsible for the biosynthesis of phytohormones are usually located in plasmids, which have been called pIAA and pCK for the biosynthesis of IAA and CKs, respectively (5,8,25). In contrast, most olive isolates have been reported to carry these genes in the chromosome (5,19).…”

Sustained growth promotion in Arabidopsis with long-term exposure to the beneficial soil bacteriumBacillus subtilis(GB03)

“…PGPR colonization has been proposed to trigger growth by bacterial synthesis of the plant hormones indole-3-acetic acid, cytokinin and gibberellins as well as by increased mineral and nitrogen availability in the soil. 4,5,6,7,8 Moreover in the absence of physical contact with plant roots, blends of bacterial volatiles devoid of traditional hormones such as auxin and GA can also trigger growth promotion. 9,10,11 Bacillus subtilis GB03, a commercially available soil symbiont, is one such strain that emits a complex blend of volatile components that activates plant growth promotion in Arabidopsis.…”