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Ensuring the perfect time to die

Researchers uncover mechanism controlling wood formation in poplar trees

Oeiras, 20.06.2013

With all its importance in our lives, wood is in fact the result of a differentiation process that ends with the programmed death of specific plant cells - the xylem cells. The correct timing for this cell death is controlled by the molecule thermospermine; in its absence, cell death occurs too fast resulting in xylem developmental defects. Researchers from the Forest Biotech Lab (iBET/ITQB-UNL) and collaborators in Sweden and in Spain have now unveiled how the levels of thermospermine are controlled in wood cells of poplar, the plant model for trees. The findings are published in The Plant Journal.

Thermospermine is a recently identified polyamine, a class of nitrogen-containing compounds that play a role in several biological processes including development. In their work, researchers tried to assess the effect of increasing the thermospermine levels in poplar trees (by overexpressing the thermospermine synthase gene) and found that this was surprisingly not possible in the xylem tissues. This evidence suggested the existence of a mechanism specific to these tissues to maintain thermospermine homeostasis.

By characterizing the crosstalk between thermospermine and the endogenous plant hormone auxin, the authors established the presence of a negative feedback loop mechanism whereby auxin positively influences thermospermine function in delaying death of the wood cells while thermospermine negatively affects endogenous auxin content in order to re-establish the equilibrium in thermospermine levels. This safeguard mechanism ensures the fundamental role of thermospermine during wood formation.

Researchers further propose that thermospermine is a xylem specific polyamine and should be considered as a novel plant growth regulator essential to ensure proper wood development. These findings are of great interest to the forest tree breeding and biotechnology community as the control of xylem cell death process during wood formation affects tree wood properties and biomass production.

Original article

The Plant Journal, DOI: 10.1111/tpj.12231

Thermospermine levels are controlled by an auxin-dependent feedback-loop mechanism in Populus xylem.

Milhinhos A, Prestele J, Bollhöner B, Matos A, Vera-Sirera F, Rambla JL, Ljung K, Carbonell J, Blázquez MA, Tuominen H, Miguel CM.


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