Bacterial genetic loci implicated in thePseudomonas putidaGR12-2R3 – canola mutualism: identification of an exudate-inducible sugar transporter

Abstract

Pseudomonas putida GR12-2R3 promotes the emergence and growth of diverse plant species. Analyses of TnphoA insertion mutations are revealing bacterial characteristics pertinent to the plant-microbe interaction. Pseudomonas putida PG269 is a TnphoA insertion derivative of GR12-2R3 that expresses canola seed exudate-inducible alkaline phosphatase (PhoA) activity. It promoted the growth of canola roots, as well as strain GR12-2R3, and outgrew its parent when they were cocultured in the presence of canola roots or in liquid seed exudate medium. (In contrast, mutant PG126 failed to promote canola root growth and was outgrown by its parent strain.) The PhoA activity of strain PG269 was induced by glucosamine and other sugars; glucosamine inhibited the growth of strain GR12-2R3 and stimulated the growth of strain PG269. Strain PG269 contained two TnphoA insertions: seiA1::TnphoA and seiB1::TnphoA. Strain PG312, which contained only insertion seiA1::TnphoA, shared all aspects of the PG269 phenotype, except the ability to outcompete strain GR12-2R3 during coculture. Insertion seiA1::TnphoA interrupted an open reading frame related in sequence to members of the MalF family of sugar transporter subunits. The PhoA-inducing fraction of canola seed exudate was hydrophilic, low in molecular weight, and heat stable. It cochromatographed with basic amino acids and amino sugars, and was inactivated by strains GR12-2R3 and PG269. Gene seiA may encode a subunit of an ABC transporter with broad specificity for glucose and related sugars whose expression can be induced by exudate sugars.

Bacterial Modulation of Plant Ethylene Levels

“…However, this does not necessarily occur because as plant ethylene levels increase, the transcription of auxin response factors is inhibited (Pierik et al, 2006;Prayitno et al, 2006;Czarny et al, 2007;Glick et al, 2007;Stearns et al, 2012), thereby limiting the extent that IAA can activate ACC synthase transcription. Moreover, some ACC is released by the roots (Bayliss et al, 1997;, taken up by the bacteria, and through the action of ACC deaminase, converted to ammonia and a-ketobutyrate. As a result, the amount of ethylene produced by the plant is reduced.…”

Expression of a Pseudomonas putida Aminotransferase Involved in Lysine Catabolism Is Induced in the Rhizosphere

“…and Pseudomonas spp. among others (5,6,19,20). Some of the genes identified in Pseudomonas fluorescens are involved in sugar transport and metabolism, amino acid transport, secretion, and oxidative stress response (19).…”

Identification of Pseudomonas proteins coordinately induced by acidic amino acids and their amides: a two-dimensional electrophoresis study

“…Exudate components are thought to attract beneficial micro-organisms to the rhizosphere and also to promote their survival in this special environment. One approach to characterize the effects of exudate components on rhizobacteria is to search for bacterial genes that are differentially expressed in the rhizosphere, or in the presence of root exudates (van Overbeek & van Elsas, 1995;Bayliss et al, 1997). Although a number of such genes have been identified, the precise roles of most of them have remained elusive.…”