The DR5 auxin response reporter uses synthetic auxin response elements to control a reporter gene. Its output reports auxin-responsive transcription, rather than directly counting auxin molecules. DR5 is a regulatory DNA arrangement, not the name of an auxin-binding fluorescent molecule.[ref]
Aux/IAA proteins repress expression of reporter genes containing natural and highly active synthetic auxin response elements by T. Ulmasov and others. Abstract, Plant Cell 9 (1997), pp. 1963–1971; DOI 10.1105/tpc.9.11.1963.
The original work compared DR5 with natural regulatory sequences in carrot cells and Arabidopsis thaliana seedlings. DR5 showed strong auxin responsiveness; a member of the auxin response factor family bound the element, while regulatory proteins could repress reporter expression. Those measurements tied the output to a transcriptional response system, rather than establishing a universal conversion from reporter intensity to hormone concentration.[ref]
Aux/IAA proteins repress expression of reporter genes containing natural and highly active synthetic auxin response elements by T. Ulmasov and others. Abstract: reporter comparison, factor binding and repression experiments.
A useful example comes from haustorium development in Phtheirospermum japonicum. DR5 expression marked a localized response near the developing organ, while separate measurements of indole-3-acetic acid tested the interpretation that hormone levels rose there. The two observations support different claims: reporter output locates a response, and chemical measurement measures the hormone. Neither should silently substitute for the other.[ref]
Local Auxin Biosynthesis Mediated by a YUCCA Flavin Monooxygenase Regulates Haustorium Development in the Parasitic Plant Phtheirospermum japonicum by Juliane K. Ishida and others. Results and Discussion: DR5 spatial response and independent IAA measurement near haustorium-forming sites.
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