That is why plants grow towards the light!

Have you ever wondered why stems grow upwards and roots downwards? Why plants always seem to turn towards the light and climbing plants run up the trellis rather than down?

The answer is simple: auxin!

But maybe not that simple, since plant hormones – and auxin is a plant hormone – are regulated by complex combinations of various processes. Elke Barbez, Jürgen Kleine-Vehn and Jirí Friml, connected to VIB and UGent recently identified an important new link in the transport of auxin through the plant, resulting in auxin being stored at specific sites. The results were published by the authoritative journal Nature.

Darwin was already interested in auxin in the 19th century. Only in recent years, however, has the hormone started to relinquish its secrets, thanks to intensive molecular research. Auxin is produced in the young, growing parts of plants and then transported throughout the plant – to a low-lying stem for example. The stem needs to straighten out as soon as possible to be able to absorb the sun's rays efficiently; therefore more auxin will be delivered to the underside of the stem than to the topside, resulting in the underside growing faster and the stem straightening out. For the same reason, plants in front of windows will always turn to the light. This dynamic regulation of auxin transport allows plants to take optimal advantage of local and changing conditions.

The transport of auxin through the plant plays a vital role. And, from all appearances, it is not a simple matter. The VIB researchers identified an important new link and means of transport for auxin: PILS proteins. PILS proteins are vital for auxin-dependent plant growth and regulate the intracellular storage of the hormone. It is exactly this compartmentalizing of auxin that seems functionally important for the various developmental processes.

Higher auxin levels at the right moment and in the right place result in better growth and greater yields. Better regulation of auxin levels would make plants grow more efficiently. The researchers hope to contribute to the development of more efficient growing processes by continuing to unravel auxin transport processes.

The study is being published in the leading journal Nature (Barbez et al., A novel putative auxin carrier family regulates intracellular auxin homeostasis in plants).

This study was conducted by Elke Barbez under the supervision of Jürgen Kleine-Vehn and Jirí Friml (VIB Department of Plant Systems Biology, UGent).

This research is jointly financed by the Vienna Science and Technology Fund (WWTF), the Agency for Innovation by Science and Technology (IWT), the Odysseus program of the Research Foundation-Flanders, the Swiss National Funds, the Ministry of Education, Youth and Sports of the Czech Republic, Grant Agency of the Czech Republic project, UGent and VIB.