Molecular Horticulture (May 2022)

Increased branching independent of strigolactone in cytokinin oxidase 2-overexpressing tomato is mediated by reduced auxin transport

  • Lilian Ellen Pino,
  • Joni E. Lima,
  • Mateus H. Vicente,
  • Ariadne F. L. de Sá,
  • Francisco Pérez-Alfocea,
  • Alfonso Albacete,
  • Juliana L. Costa,
  • Tomáš Werner,
  • Thomas Schmülling,
  • Luciano Freschi,
  • Antonio Figueira,
  • Agustin Zsögön,
  • Lázaro E. P. Peres

DOI
https://doi.org/10.1186/s43897-022-00032-1
Journal volume & issue
Vol. 2, no. 1
pp. 1 – 19

Abstract

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Abstract Tomato production is influenced by shoot branching, which is controlled by different hormones. Here we produced tomato plants overexpressing the cytokinin-deactivating gene CYTOKININ OXYDASE 2 (CKX2). CKX2-overexpressing (CKX2-OE) plants showed an excessive growth of axillary shoots, the opposite phenotype expected for plants with reduced cytokinin content, as evidenced by LC-MS analysis and ARR5-GUS staining. The TCP transcription factor SlBRC1b was downregulated in the axillary buds of CKX2-OE and its excessive branching was dependent on a functional version of the GRAS-family gene LATERAL SUPPRESSOR (LS). Grafting experiments indicated that increased branching in CKX2-OE plants is unlikely to be mediated by root-derived signals. Crossing CKX2-OE plants with transgenic antisense plants for the strigolactone biosynthesis gene CAROTENOID CLEAVAGE DIOXYGENASE (CCD7-AS) produced an additive phenotype, indicating independent effects of cytokinin and strigolactones on increased branching. On the other hand, CKX2-OE plants showed reduced polar auxin transport and their bud outgrowth was reduced when combined with auxin mutants. Accordingly, CKX2-OE basal buds did not respond to auxin applied in the decapitated apex. Our results suggest that tomato shoot branching depends on a fine-tuning of different hormonal balances and that perturbations in the auxin status could compensate for the reduced cytokinin levels in CKX2-OE plants.

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