Transcription analyses of GmICHG, a gene coding for a β-glucosidase that catalyzes the specific hydrolysis of isoflavone conjugates in Glycine max (L.) Merr

• GmICHG is a β-glucosidase that is exclusively localized in the root apoplast of soybean.
• GmICHG plays a constitutive role in the production of free isoflavones in the roots.
• Upon wounding and fungal infection of cotyledons, GmICHG was transiently up-regulated in taproots.
• Such long-distance up-regulation was not observed with either GmIFS or GmIF7GT.
• Transcription of GmICHG in the roots was sensitive to abiotic stresses on the roots.

Isoflavone conjugate-hydrolyzing β-glucosidase (GmICHG) of soybeans [Glycine max (L.) Merr.] catalyzes the specific hydrolysis of isoflavone conjugates (β-7-O-(malonyl)glucosides of isoflavones) to produce free isoflavones. In this study, changes in the transcription levels of GmICHG in the individual organs of soybean seedlings (cv. Enrei) in response to microbial infection and abiotic stresses were analyzed and compared with those of genes coding for 2-hydroxyisoflavanone synthase (GmIFS) and isoflavone 7-O-glucosyltransferase (GmIF7GT). GmICHG was originally expressed in abundance only in the roots and at low levels only in the other organs. The transcription of GmICHG in the roots and other organs was suppressed upon infection of the roots by Phytophthora sojae. Upon wounding of the cotyledon, a transient long-distance up-regulation of GmICHG transcription in the roots was observed; upon fungal infection in the cotyledon, however, a delayed elevation of GmICHG transcription took place in the roots with the maximum at 10 h after the infection. Such long-distance up-regulation patterns were not observed with either GmIFS or GmIF7GT. The transcription levels of GmICHG remained essentially unchanged upon treatment of the roots with Bradyrhizobium japonicum. The transcription of GmICHG in the roots was also sensitive to a variety of stresses on the roots, such as flooding, elicitation with yeast extract, drought, and treatment with plant hormones such as abscisic, salicylic, and jasmonic acids and ethylene.