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European Journal of Plant Pathology

, Volume 128, Issue 3, pp 289–302 | Cite as

The type III effector PthG of Pantoea agglomerans pv. gypsophilae modifies host plant responses to auxin, cytokinin and light

  • Dan M. Weinthal
  • Sara Yablonski
  • Sima Singer
  • Isaac Barash
  • Shulamit Manulis-Sasson
  • Victor Gaba
Article

Abstract

Pantoea agglomerans pvs. gypsophilae and betae are related gall-forming bacteria. While P. agglomerans pv. beta initiates gall formation on both beet and gypsophila, the gypsophila pathovar causes gall formation only on gypsophila. PthG is a type III effector determining host range of these pathogens, initiating the hypersensitivity response in beet, but is a virulence factor in gypsophila. The role of PthG and its mode of action in pathogenicity remain unclear. Transgenic Nicotiana tabacum plants expressing pthG were created. PthG over-expression was often lethal, and surviving pthG-bearing lines showed morphological and developmental abnormalities such as leaf deformation and abnormal vascular branching, dwarf stature, loss of apical dominance, seedling apical meristem loss, rapid germination, reduced fertility, plants which cease growth for several weeks later producing a new lateral shoot, and loss of endophyte resistance (bearing unusual saprophyte populations). Some transformants required light for seed germination and showed rapid seedling greening. In in vitro assays PthG expression modified responses to auxin and cytokinin, inhibiting root and shoot production but not callus formation. In vitro differentiation responses to light were modified by PthG expression. This effector may interfere in the plant auxin signalling pathways resulting in higher observed auxin and ethylene levels, and subsequent blockage of root and shoot development. Apparently PthG tunes the host response to high hormone levels, changing the developmental response. Since shoot and root development are delayed, we hypothesize that callus/gall formation is supported by this activity. However, interference by PthG with hormone and light signalling does not explain all the responses observed in pthG-bearing lines.

Keywords

Shoot formation Root formation Callus Tissue culture Transgenic plants Transgenic tobacco 

Abbreviations

BA

Benzyl adenine

CT

Cycle threshold

GA3

Gibberellic acid

HR

Hypersensitive response

hrc

hrp conserved

hrp

Hypersensitive response and pathogenicity

IAA

Indole-3-acetic acid

LB

Luria Broth

MS

Murashige and Skoog (1962) medium

NAA

1-naphthaleneacetic acid

Pab

P. agglomerans pv. betae

Pag

P. agglomerans pv. gypsophilae

PDA

Potato dextrose agar

qRT-PCR

Quantitative reverse transcriptase (Real Time) PCR

STS

Silver thiosulphate

T3SS

Type III secretion system

TC

Transgenic (“empty vector”) control

Notes

Acknowledgements

Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 517/09. The authors thank Dr. Amnon Lichter for help with qRT-PCR, Daniel Chalupowicz for help with ethylene measurements, and Prof. H. Fromm for critical comments on the ms.

Supplementary material

10658_2010_9666_MOESM1_ESM.docx (1.1 mb)
Supplementary Figure 1 pthG-bearing cv. Samsun NN lines can carry a greater endophyte microbial population. (A) Transgenic empty vector control and (B) pthG line 44733 in tissue culture were sampled, disinfected and incubated on PDA medium at 25°C for 5 days. (DOCX 1159 kb)

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Copyright information

© KNPV 2010

Authors and Affiliations

  • Dan M. Weinthal
    • 1
    • 2
    • 3
  • Sara Yablonski
    • 1
  • Sima Singer
    • 1
  • Isaac Barash
    • 2
  • Shulamit Manulis-Sasson
    • 1
  • Victor Gaba
    • 1
  1. 1.Department of Plant Pathology and Weed ScienceARO Volcani CenterBet DaganIsrael
  2. 2.Department of Plant Sciences, Faculty of Life SciencesUniversity of Tel AvivTel AvivIsrael
  3. 3.Department of Molecular, Cellular and Developmental BiologyThe University of MichiganAnn ArborUSA

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