Cytokinin induces expansin gene expression in Melilotus alba Desr. wild-type and the non-nodulating, non-mycorrhizal (Nod-Myc-) mutant Masym3

• Published in: Plant signaling & behavior 2008-04, Vol.3 (4), p.218-223
• Main Authors: Lee, Angie, Giordano, Walter, Hirsch, Ann M.
• Format: Article
• Language: English
• Subjects: Binding; Biology; Bioscience; Calcium; Cancer; Cell; Cycle; Landes; Organogenesis; Proteins; Research Paper
• ISSN: 1559-2316; 1559-2324; 1559-2324
• DOI: 10.4161/psb.3.4.5317

We previously showed that applying 10 -6 M of the cytokinin 6-benzylaminopurine (BAP) to uninoculated roots of Masym3, a Nod - Myc - Melilotus alba (Desr.) mutant, resulted in the accumulation of MaENOD40 transcripts to levels similar to BAP-treated wild-type roots. In contrast, inoculation with a Nod - S. meliloti mutant expressing the trans-zeatin synthase gene of Agrobacterium tumefaciens (Nod - /pTZS + ) did not induce MaENOD40 transcript accumulation in either wild-type or Masym3 roots. However, Masym3 root hairs became swollen at their tips following inoculation with wild-type or Nod - /pTZS + rhizobia. Because root hair distention and elongation are often correlated with increased expansin activity, we investigated whether BAP treatment or inoculation with Nod - /pTZS + S. meliloti upregulated the expression of expansion mRNAs. We first determined that treating wild-type roots with 10 -5 or 10 -6 M BAP resulted in greater MaEXPA1 transcript accumulation than treating roots with comparable concentrations of the auxin NAA. When Masym3 roots were treated with 10 -6 M BAP, MaEXPA1 mRNAs accumulated to levels comparable to wild-type roots. We then showed that MaEXPA1 mRNAs accumulated in wild-type M. alba roots in response to the Nod-/pTZS+ S. meliloti strain. Masym3 mutant roots inoculated with Nod - /pTZS + rhizobia were also upregulated for MaEXPA1 expression.