Plant Molecular Biology

, Volume 70, Issue 1–2, pp 113–122

Altered ARA2 (RABA1a) expression in Arabidopsis reveals the involvement of a Rab/YPT family member in auxin-mediated responses

  • Eun-Ji Koh
  • Ye-Rim Kwon
  • Kang-Il Kim
  • Suk-Whan Hong
  • Hojoung Lee
Article

Abstract

Ras super family proteins serve as molecular switches regulating many different cellular processes. However, given the large number of family members, sequence information has provided little insight into the function of individual proteins. This study examined phenotypic alterations in an Arabidopsisara2 mutant, in which a Ras super family member-encoding gene is disrupted by a T-DNA insertion. Although one mutant line (Salk_013811) was hypersensitive to auxin, its T-DNA insertion was in the 5′-UTR of ARA2. Thus, we examined a true ARA2 knock-out mutant (Salk_077747) which contains an insertion in the first exon of ARA2. We found that ARA2 expression is responsive to auxin and at low concentrations, ara2 mutant plants exhibit increased numbers of lateral roots. ARA2 overexpression causes plants to exhibit hypersensitivity to auxin, due to altered expression of auxin-responsive genes, and these plants exhibited reduced numbers of lateral roots. A GFP-ARA2 fusion protein localized to the endosomes, suggesting that ARA2 may play a role in vesicle trafficking of components involved in polar auxin transport. Taken together, these results show that ARA2 is an essential component of a pathway that couples auxin signaling to plant growth and development.

Keywords

Arabidopsis thaliana Auxin ARA2 NPA Auxin-responsive genes 

Supplementary material

11103_2009_9460_MOESM1_ESM.jpg (63 kb)
Fig. S1Identification of Salk_013811. a After 3 days of stratification at 4°C, seeds were germinated and grown for 14 days under the conditions indicated. Under control conditions, plants were grown in standard MS-agar supplemented with 2% sucrose. Under IAA conditions, the agar also contained 1 μM IAA. In addition, wild-type and ara2-1 (Salk_013811) seeds were exposed to NPA (1-N-naphthylphthalamic acid), a non-competitive inhibitor of auxin anion efflux carriers that blocks polar transport of auxin. Ten-day-old wild-type and ara2-1 mutant seedlings were grown on MS agar in the presence or absence of 10 μM NPA. All seedlings were incubated in a growth chamber under continuous white light. b Quantitation of wild-type and ara2-1 root lengths from (a). The values are means (±SE) for 60 seedlings from three independent experiments (20 seedlings per experiment). * P < 0.05 versus controls. (JPG 64 kb)
11103_2009_9460_MOESM2_ESM.jpg (46 kb)
Fig. S2Schematic showing the T-DNA insertion in ara2-1. a The T-DNA was inserted at −31 bp in the 5′-UTR of ARA2. b Northern blot analysis of ARA2 transcript levels in ara2-1 plants. Two-week-old wild-type and ara2-1 plants were harvested following treatment with auxin. UBQ11 expression was used as a loading control. (JPG 47 kb)
11103_2009_9460_MOESM3_ESM.jpg (32 kb)
Fig. S3Northern blot analysis of auxin-responsive genes in wild-type, ara2-2 and ARA2-OX plants. Expression profiles of auxin-responsive genes in 3-week-old wild-type, ara2-2 and ARA2-OX plants following treatment with 1 μM 2,4-D. ARA2 and IAA17 transcript levels were monitored by Northern blot analysis and rRNA was used as a loading control. (JPG 33 kb)
11103_2009_9460_MOESM4_ESM.jpg (65 kb)
Fig. S4The ARA2 gene is not induced by cytokinin. After sterilization and 3 days of stratification at 4°C, seeds were germinated in standard MS agar supplemented with 2% sucrose and various concentrations of cytokinin (0, 0.01, 0.1, 1 or 10 μM BAP), and allowed to grow for three weeks. Expression profiles of ARA2 in 3-week-old wild-type, ara2-2 and ARA2-OX plants are shown following treatment with 0.01, 0.1, 1 or 10 μM BAP. The ARA2 transcript levels were examined by Northern blot analysis and rRNA was used as a loading control. (JPG 66 kb)

Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  • Eun-Ji Koh
    • 1
  • Ye-Rim Kwon
    • 1
  • Kang-Il Kim
    • 2
  • Suk-Whan Hong
    • 2
  • Hojoung Lee
    • 1
  1. 1.Division of Biotechnology, College of Life Sciences and BiotechnologyKorea UniversitySeoulRepublic of Korea
  2. 2.Division of Applied Plant Science, College of Agriculture and Life SciencesChonnam National UniversityGwangjuKorea

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