Auxin is a tiny signaling molecule—about the size of an amino acid—that coordinates plant growth and development. It is ephemeral: auxin appears and disappears quickly throughout all plant tissues, moving between cells to deliver its messages. The most common tool for measuring auxin, DR5-GFP, is not very sensitive to the molecule’s rapid flux, in part because GFP (green fluorescent protein) is a slow-maturing reporter.
Teva Vernoux and colleagues at the University of Lyon have created a tool to track the elusive molecule, dubbed DII-VENUS. Auxin controls gene expression by initiating the degradation of Aux/IAA proteins, nuclear proteins that inhibit transcription factors from activating auxin’s target genes. The researchers expressed a fast-maturing version of a yellow fluorescent protein, VENUS, by fusing it to the auxin response domain of the Aux/IAA proteins. Thus, when auxin binds Aux/IAA, VENUS’s glow also disappears.
Tracing the disappearance of VENUS, however, is “one of its limitations, because it’s always a little scary when you’re looking for the absence of a signal,” says plant biologist Jennifer Nemhauser of the University of Washington. (Nature, 482:103-08, 2012). 
.
| STATS TALK | |||||
| COMPARING METHODS: | REPORTER MATURATION | REQUIRES | SIGNAL DETECTION | RESPONSE | |
| DR5-GFP | 1.5–2 hours | De novo GFP synthesis | Appearance | Less dynamic | |
| DII-VENUS | 6.5 minutes | Aux/IAA degradation | Fade | More dynamic | |
