Abstract Detail
Plant-Symbiont Interactions Subramanian, Senthil [1], Stacey, Gary [2], Yu, Oliver [3]. Isoflavone mediated auxin-transport regulation is not critical for soybean nodulation by Bradyrhizobium japonicum. Legume flavonoids have been implicated in the nodulation process, but until recently no unequivocal evidence existed showing that these compounds are essential for nodulation. We show that silencing of isoflavone biosynthesis in soybean hairy roots led to severely reduced nodulation suggesting that these compounds are indeed essential for nodulation. Soybean roots produce determinate nodules when colonized by Bradyrhizobium japonicum and isoflavones are the primary inducers of nod gene expression in this species. Silencing of IFS resulted in altered auxin-inducible gene expression and auxin transport consistent with a role for isoflavones as endogenous regulators of auxin transport in soybean roots. We used genistein-hypersensitive B. japonicum mutant cells to differentiate between the roles of isoflavones as nod gene inducers and auxin transport regulators. These cells rescued normal nodulation in IFS-silenced roots, indicating that the ability of isoflavones to modulate auxin transport is not essential to nodulation. Consistently, no block in auxin transport was observed at the site of rhizobial inoculation in soybean roots. Medicago truncatula roots produce indeterminate nodules when colonized by Sinorhizobium meliloti. Recently, Ulrike Mathesius’ lab showed that M. truncatula roots show a clear block in auxin transport at the site of rhizobial inoculation unlike soybean roots. Flavonoid-null M. truncatula roots lacked this block in auxin transport and failed to nodulate. We present a model for the roles of flavonoids during nodulation in determinate nodule forming legumes such as soybean and indeterminate nodule forming legumes such as M. truncatula.
Log in to add this item to your schedule
Related Links:
Subramanian et al (2006) Plant J 48(2):261-73
Wasson et al (2006) Plant Cell 18(7):1617-29
1 - Donald Danforth Plant Science Center, 975 North Warson road, St Louis, MO, 63132, USA
2 - University of Missouri, Columbia, MO, National Center for Soybean Biotechnology, Divisions of Plant Sciences and Biochemmistry, Department of Molecular Microbiology and Immunology
3 - Donald Danforth Plant Science Center
Keywords:
nodulation
auxin
flavonoids
Soybean.
Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P16001
Abstract ID:148 | 