Regulation and manipulation of ABA biosynthesis in roots

Authors

  • ANDREW J. THOMPSON,

    Corresponding author
    1. Warwick-HRI, Wellesbourne, University of Warwick, Warwickshire, CV35 9EF, and
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  • BARRY J. MULHOLLAND,

    1. Warwick-HRI, Wellesbourne, University of Warwick, Warwickshire, CV35 9EF, and
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    • *

      Present address: Duchy College, Rosewarne, Camborne, Cornwall TR14 OAB, UK.

  • ALISON C. JACKSON,

    1. Warwick-HRI, Wellesbourne, University of Warwick, Warwickshire, CV35 9EF, and
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  • JOHN M. T. MCKEE,

    1. Warwick-HRI, Wellesbourne, University of Warwick, Warwickshire, CV35 9EF, and
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  • HOWARD W. HILTON,

    1. Warwick-HRI, Wellesbourne, University of Warwick, Warwickshire, CV35 9EF, and
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  • RACHAEL C. SYMONDS,

    1. Department of Plant Sciences, School of BioSciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK
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    • Present address: Liverpool John Moores University, UK.

  • TINEKE SONNEVELD,

    1. Department of Plant Sciences, School of BioSciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK
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  • ALAN BURBIDGE,

    1. Department of Plant Sciences, School of BioSciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK
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  • PATRICK STEVENSON,

    1. Department of Plant Sciences, School of BioSciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK
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    • Present address: University of Southampton, UK.

  • IAN B. TAYLOR

    1. Department of Plant Sciences, School of BioSciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK
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Dr Andrew J. Thompson. Fax: +44 (0) 24 7657 4500; e-mail: a.j.thompson@warwick.ac.uk

ABSTRACT

Overexpression of 9-cis-epoxycarotenoid dioxygenase (NCED) is known to cause abscisic acid (ABA) accumulation in leaves, seeds and whole plants. Here we investigated the manipulation of ABA biosynthesis in roots. Roots from whole tomato plants that constitutively overexpress LeNCED1 had a higher ABA content than wild-type (WT) roots. This could be explained by enhanced in situ ABA biosynthesis, rather than import of ABA from the shoot, because root cultures also had higher ABA content, and because tetracycline (Tc)-induced LeNCED1 expression caused ABA accumulation in isolated tobacco roots. However, the Tc-induced expression led to greater accumulation of ABA in leaves than in roots. This demonstrates for the first time that NCED is rate-limiting in root tissues, but suggests that other steps were also restrictive to pathway flux, more so in roots than in leaves. Dehydration and NCED overexpression acted synergistically in enhancing ABA accumulation in tomato root cultures. One explanation is that xanthophyll synthesis was increased during root dehydration, and, in support of this, dehydration treatments increased β-carotene hydroxylase mRNA levels. Whole plants overexpressing LeNCED1 exhibited greatly reduced stomatal conductance and grafting experiments from this study demonstrated that this was predominantly due to increased ABA biosynthesis in leaves rather than in roots. Genetic manipulation of both xanthophyll supply and epoxycarotenoid cleavage may be needed to enhance root ABA biosynthesis sufficiently to signal stomatal closure in the shoot.

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