Plant and Soil

, Volume 405, Issue 1–2, pp 81–96 | Cite as

Development of root system architecture of Arabidopsis thaliana in response to colonization by Martelella endophytica YC6887 depends on auxin signaling

  • Ajmal Khan
  • Mohammad Tofajjal Hossain
  • Hyeong Cheol Park
  • Dae-Jin Yun
  • Sang Hee Shim
  • Young Ryun Chung
Regular Article


Background and aims

Many rhizobacteria promote plant growth by producing hormones that stimulate the development of plant root system and increase plant biomass. The aim of this study was to investigate the growth promotion activity of the bacterial strain Martelella endophytica YC6887 and elucidate the signaling pathways potentially involved in Arabidopsis interaction with M. endophytica YC6887.


The growth regulation was evaluated by inoculation of strain YC6887 with wild-type Arabidopsis Col-0 seedlings and mutants defective in auxin aux1-7, axr4-2, eir1-1, ethylene ein2-1, etr1-3, jasmonic acid signaling jar1, and root hair deficient mutant rhd6. The auxin response was further determined by using transgenic line DR5::GUS and a polar auxin transport inhibitor, 1-N-naphthylphthalamic acid (NPA).


M. endophytica YC6887 increased the number of lateral roots and plant biomass of Arabidopsis by producing phenylacetic acid. The growth promotion and improved lateral root development by the bacterium decreased in the auxin related mutants, whereas the ethylene and jasmonic acid mutants had a wild type response. The strain YC6887 increased root hair density in wild type Col-0 and recovered the root hair forming ability in root hair deficient mutant rhd6. Moreover, strain YC6887 treatment showed distinct response in DR5::GUS transgenic line compared to the control. Strain YC6887 lost its growth-promoting activity in the presence of NPA, an auxin transport inhibitor. This indicated that strain YC6887 activated the auxin signaling mechanism.


Our results showed that M. endophytica YC6887 promoted plant growth in terms of plant biomass and root system development. Arabidopsis root system development upon M. endophytica YC6887 colonization was dependent on auxin signaling, but independent of ethylene and jasmonic acid signaling.


Lateral root primordia Martelella endophytica Phenylacetic acid Root system architecture (RSA) 



(Indole-3-acetic acid)


(Lateral root primordia)


(1-N-Naphthylphthalamic acid)


(Phenylacetic acid)



This work was supported by the Brain Korea (BK) 21 Plus project, the Ministry of Education, Science and Technology, Republic of Korea and was partially funded by a Research and Business Development grant provided by the Ministry of Food, Agriculture, Forestry and Fisheries, Korea (no. 808015–3). We thank Jae Yean Kim from Gyeongsang National University for providing the Arabidopsis mutants, ein2-1 and DR5::GUS and also thank Malcolm J. Bennett, University of Nottingham, for providing the auxin mutants, aux1-7, axr4-2 and eir1-1.

Supplementary material

11104_2015_2775_MOESM1_ESM.doc (4.8 mb)
Fig. S1 The roots of Arabidopsis (Col-0) plants were drenched with the suspension of Martelella endophytica YC6887 in buffer solution (10 mM MgSO4) at 2 × 106, 5 × 107, and 5 × 108 CFU mL−1. Buffer was used as a control. Representative plants showed growth one week after inoculation of the strain YC6887. (DOC 4921 kb)
11104_2015_2775_MOESM2_ESM.doc (60 kb)
Fig. S2 Effect of PAA on root system development of auxin mutants aux1-7, axr4-2, and eir1-1. a lateral root number/seedling and b primary root length. Black bars represent untreated seedlings control. Gray bars indicate phenylacetic acid treated seedlings. Means ± standard error within bars are significantly different (Duncan’s test; P < 0.05). (DOC 59 kb)
11104_2015_2775_MOESM3_ESM.doc (60 kb)
Fig. S3 Effect of PAA and IAA on primary root length of Arabidopsis. a nano molar concentration and b micro molar concentration. Black circle shows different concentration of PAA. White circles shows IAA. (DOC 60 kb)
11104_2015_2775_MOESM4_ESM.doc (2.3 mb)
Fig. S4 Structure determination of phenylacetic acid, a chemical structure of phenylacetic acid, b 1H-NMR spectrum, c 13C-NMR spectrum and d EI-MS spectrum. (DOC 2305 kb)
11104_2015_2775_MOESM5_ESM.doc (3 mb)
Fig. S5 Effect of NPA (10 μM) on DR5::GUS transgenic lines. a control, b Martelella endophytica YC6887, c only NPA, and d NPA with M. endophytica YC6887 treated DR5::GUS transgenic line. LRP of DR5::GUS transgenic lines after Gus staining, e LRP of control seedlings, f LRP of PAA, and g LRP of M. endophytica YC6887 treated plants (scale bar = 100 μm). (DOC 3074 kb)
11104_2015_2775_MOESM6_ESM.doc (1.1 mb)
Fig. S6 Effect of PAA at different concentrations (4 μm and 8 μm) on primary root and LRP formation in DR5::GUS seedlings. a Primary root tip of control, b and c PPA treated DR5::GUS seedlings (scale bar = 100 μm), d LRP formation in control and PAA treated DR5::GUS seedlings (scale bar = 200 μm). (DOC 1145 kb)


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Copyright information

© Springer International Publishing Switzerland 2016

Authors and Affiliations

  • Ajmal Khan
    • 1
  • Mohammad Tofajjal Hossain
    • 1
  • Hyeong Cheol Park
    • 2
  • Dae-Jin Yun
    • 1
  • Sang Hee Shim
    • 3
  • Young Ryun Chung
    • 1
  1. 1.Division of Applied Life Science (BK21 Plus), Plant Molecular Biology and Biotechnology Research CenterGyeongsang National UniversityJinjuRepublic of Korea
  2. 2.Department of Climate & EcologyNational Institute of Ecology (NIE)SeocheonRepublic of Korea
  3. 3.College of PharmacyDuksung Women’s UniversitySeoulRepublic of Korea

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