Quantifying morphogenetic responses in living plants

Auxin is the “conductor” of plant morphogenesis. Highly sensitive sensors and reporters now allow the dynamics of auxin distribution and auxin-induced transcription to be followed quantitatively in living tissues.

HFSP Program Grant holder Teva Vernoux and colleagues
authored on Fri, 01 May 2015

Auxin, the first plant hormone discovered (from work initiated by Darwin), is the central morphogenetic regulator of plants. Dynamic and plastic reconfiguration of auxin distribution through both short- and long-distance transport systems is in large partly responsible for reiterative organogenesis in plants, allowing plants to continuously shape their architecture and adapt it to environmental conditions. The main form of auxin, indole-acetic acid, is a small molecule derived from tryptophane, making it difficult to detect in tissues by classical immuno-cytochemical approaches. It is only recently that DII-VENUS, a synthetic protein degraded directly upon auxin perception, was developed to detect auxin from work led by HFSP grant holder and former Career Development Awardee Teva Vernoux (CNRS/Ecole Normale Supérieure, Lyon). High-affinity binding sites for transcription factors mediating auxin responses, the Auxin Response Factors (ARFs), have also been recently identified by the group of Dolf Weijers at the University of Wagenigen.

The two groups have collaborated to produce a new generation of sensors and reporters to quantify the spatio-temporal distribution of both concentrations of and transcriptional responses to this key morphogenetic molecule in living tissues. They generated a ratiometric version of DII-VENUS by co-expressing the DII-VENUS protein (Yellow) with a tdTomato red fluorescent protein fusion that is not degradable by auxin. Quantification of the Yellow to Red ratios during development allows how auxin gradients are established and maintained during plant development to be followed with high spatio-temporal precision. A transcriptional reporter consisting in a synthetic promoter constructed from the high-affinity ARF binding sites driving a fluorescent protein provides in parallel a highly sensitive tool to visualize auxin-induced transcriptional output. Combination of these two tools should allow both auxin distribution and responses to correlate in real time, thus allowing us to understand how information provided by a plant morphogenetic regulator is translated during patterning, which is one of the goals of the ongoing HFSP grant coordinated by Teva Vernoux. This work provides a toolbox for understanding plant development and might hold the key to the generation of plants with architectures adapted to changing environmental conditions, one of the main challenges of tomorrow’s agriculture.

Reference

Reporters for sensitive and quantitative measurement of auxin responses. Liao C, Smet W, Brunoud G, Yoshida S, Vernoux T & Weijers D. (2015) Nature Methods 12:207-210.

Pubmed link