Evaluation of auxin-responsive genes in soybean for detection of off-target plant growth regulator herbicides

Abstract

The expression of a candidate auxin-responsive gene was evaluated for use in a diagnostic assay for plant growth regulator (PGR) herbicide injury in soybean leaves. Expression ofGH3, a primary auxin-responsive gene, was evaluated in response to dicamba and clopyralid at the RNA and protein levels, and proteomic analysis evaluated global expression of proteins in response to dicamba. Expression ofGH3was also analyzed in response to heat, drought, salt stress, and infection by soybean mosaic virus (SMV) and bean pod mottle virus (BPMV) to determine the specificity ofGH3expression as a diagnostic marker for PGR herbicide injury. At the RNA level,GH3was strongly induced by dicamba and clopyralid within 8 h after application. Expression peaked 1 to 3 d after treatment (DAT) in response to 10% and 1% of a labeled dose of dicamba and clopyralid, with higher expression levels detected at higher herbicide rates. At the protein level, GH3 expression was also strongly induced at 1, 2, and 3 DAT by 10% vs. 1% of a labeled dose of dicamba and clopyralid. Heat, drought, and salt stress and infection with SMV or BPMV had no effect onGH3expression at either the RNA or protein level. Proteomic analysis identified three proteins that were up-regulated in response to dicamba. Two were induced for less than 7 DAT, and a third was identified as a stress-response enzyme (superoxide dismutase) that is likely not specific to PGR herbicide injury. Expression ofGH3was highly induced by PGR herbicides at the RNA and protein level and was not affected by environmental stresses or viral infection, indicating thatGH3expression has excellent potential for use in a diagnostic assay for PGR herbicide injury.