A joint study published in Cell (doi.org/10.1016/j.cell.2013.12.027) by the teams headed by Miquel Coll at the Institute for Research in Biomedicine (IRB Barcelona) –based in the Parc Científic de Barcelona– and the Institute of Molecular Biology of CSIC, both in Barcelona, and Dolf Weijers at the University of Wageningen, in the Netherlands, unravels the mystery behind how the plant hormones called auxins activate multiple vital plant functions through various gene transcription factors.

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Auxins are plant hormones that control growth and development, that is to say, they determine the size and structure of the plant. Among their many activities, auxins favor cell growth, root initiation, flowering, fruit setting and delay ripening. Auxins have practical applications and are used in agriculture to produce seedless fruit, to prevent fruit drop, and to promote rooting, in addition to being used as herbicides. The biomedical applications of these hormones as anti-tumor agents and to facilitate somatic cell reprogramming (the cells that form tissues) to stem cells are also being investigated.

The effects of auxins in plants was first observed by Darwin in 1881, and since then this hormone has been the focus of many studies. However, although it was known how and where auxin is synthesized in the plant, how it is transported, and the receptors on which it acts, it was unclear how a hormone could trigger such diverse processes.

At the molecular level, the hormone serves to unblock a transcription factor, a DNA-binding protein, which in turn activates or represses a specific group of genes. Some plants have more than 20 distinct auxin-regulated transcription factors. They are called ARFs (Auxin Response Factors) and control the expression of numerous plant genes in function of the task to be undertaken, that is to say, cell growth, flowering, root initiation, leaf growth etc.

Using the Synchrotron Alba, in Cerdanyola del Vallès (Barcelona), and the European Synchrotron, in Grenoble, structural biologist Dr. Miquel Coll and his team analyzed the DNA binding mode used by various ARFs.

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