Original Article

Journal of Plant Research

, Volume 115, Issue 6, pp 439-447

First online:

A white clover nodulin gene, dd23b, encoding a cysteine cluster protein, is expressed in roots during the very early stages of interaction with Rhizobium leguminosarum biovar trifolii and after treatment with chitolipooligosaccharide Nod factors

  •  M. CrockardAffiliated withApplied Plant Science Division, Department of Agriculture and Rural Development (NI), Newforge Lane, Belfast BT9 5PX, UK
  • ,  A. BjoursonAffiliated withSchool of Biomedical Sciences, University of Ulster, Coleraine Campus, Coleraine, Co. Londonderry, UK
  • ,  F. DazzoAffiliated withDepartment of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, USA
  • , James CooperAffiliated withApplied Plant Science Division, Department of Agriculture and Rural Development (NI), Newforge Lane, Belfast BT9 5PX, UK

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Abstract.

An early nodulin cDNA, dd23b, was isolated from white clover root tissue by differential display RT-PCR. Its full-length sequence of 340 nucleotides encodes a predicted 72-amino-acid protein of molecular mass 8.3 kDa, with a polypeptide region containing cysteine pairs spaced in the manner of a cysteine cluster protein. This feature, which is shared by some other late and early nodulins from pea and broad bean, suggests a role in metal ion binding and membrane transport. Temporal and spatial expression patterns were determined during infection and nodulation by the homologous microsymbiont. No expression was found in unchallenged root tissue over a 7-day sampling period. Expression was first detectable in roots by RT-PCR 6 h post-inoculation with Rhizobium leguminosarum biovar trifolii, placing dd23b among the earliest nodulins to be detected to date. In root nodules, expression occurred primarily in the central symbiotic zone, but also in some host cells within the infection zone. Addition of purified wild-type chitolipooligosaccharide Nod factor to axenic white clover roots induced dd23b expression, providing further evidence for the role of this gene in the early plant response to infection by rhizobia.

chitolipooligosaccharide Nod factor Cysteine cluster protein Differential display RT-PCR Early nodulin Rhizobia Trifolium repens