Plant Physiology Preview
Published on February 13, 2009; 10.1104/pp.109.135475
OPEN ACCESS ARTICLE
Received January 8, 2009
Accepted February 3, 2009
Roles for Auxin, Cytokinin and Strigolactone in Regulating Shoot Branching
Brett J Ferguson and Christine A Beveridge *
School of Integrative Biology and ARC Centre of Excellence for Integrative Legume Research, The University of Queensland, St Lucia, QLD, 4072, Australia
* Corresponding author; email: c.beveridge{at}uq.edu.au.
Many processes have been described in the control of shoot branching. Apical dominance is defined as the control exerted by the shoot tip on the outgrowth of axillary buds, whereas correlative inhibition includes the suppression of growth by other growing buds or shoots. The level, signalling and/or flow of the plant hormone, auxin, in stems and buds is thought to be involved in these processes. In addition, RMS branching genes in pea control the synthesis and perception of a long-distance inhibitory branching signal produced in the stem and roots, a strigolactone or product. Auxin treatment affects the expression of RMS genes, but it is unclear whether the RMS network can regulate branching independently of auxin. Here we explore whether apical dominance and correlative inhibition show independent or additive effects in rms mutant plants. Bud outgrowth and branch lengths are enhanced in decapitated and stem-girdled rms mutants compared with intact control plants. This may relate to an RMS-independent induction of axillary bud outgrowth by these treatments. Correlative inhibition was also apparent in rms mutant plants, again indicating an RMS-independent component. Treatments giving reductions in RMS1 and RMS5 gene expression, auxin transport and auxin level in the main stem were not always sufficient to promote bud outgrowth. We suggest this may relate to a failure to induce the expression of cytokinin biosynthesis genes, which always correlated with bud outgrowth in our treatments. We present a new model that accounts for apical dominance, correlative inhibition, RMS gene action, auxin and cytokinin and their interactions in controlling the progression of buds through different control points from dormancy to sustained growth.
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