1. www.cilr.uq.edu.au ARC Centre of Excellence for Integrative Legume Research How Legumes Make Nodules Lisette Pregelj – Education and Outreach Manager

2. www.cilr.uq.edu.au Legume Nodules Legume nodules are special plant organs that house nitrogen- fixing bacteria called Rhizobium Nodules form on Legume roots Nodules can also form on stems in some species

3. www.cilr.uq.edu.au

4. Rhizobium Filled Cells >25,000 per cell Nodule Cross-Section Sclerenchyma Vascular Bundles Nodule Cortex

5. www.cilr.uq.edu.au Nodule Formation 1. Rhizobia attracted to root 2. Rhizobia attach to root hairs 3. Root hair curling 4. Infection thread formation

6. www.cilr.uq.edu.au Nodule Formation 5. Root cortical cell division 6. Rhizobia invade cortical cells 7. The nodule grows 8. Fully functional nodule

7. www.cilr.uq.edu.au 1: Rhizobia attracted to root

8. www.cilr.uq.edu.au 1. Rhizobia attracted to root Legume roots exude flavonoids (Soybean exudes the isoflavone genistein) Rhizobia are attracted to flavonoids Petri dish contains a bacterial lawn Bacteria turn blue when a reporter gene is switched on by plant exudates (flavonoids)

9. www.cilr.uq.edu.au 10  m 2. Rhizobia attach to root hairs Rhizobia Root Hair

10. www.cilr.uq.edu.au 2. Rhizobia attach to root hairs Deformed root hairs Curled root hair Vascular bundle

11. www.cilr.uq.edu.au 50 mm 3. Root hair curling

12. www.cilr.uq.edu.au 4. Rhizobia infect root hair Root Hair Root Hair Curling Rhizobia Infection Thread Legume Root Infection Pocket Vascular Bundle

13. www.cilr.uq.edu.au 50  m 4. Rhizobia infect root hair

14. www.cilr.uq.edu.au 100  m 5. Root cortical cells divide

15. www.cilr.uq.edu.au 100  m 5. Root cortical cells divide

16. www.cilr.uq.edu.au 50  m 6. Rhizobia invade cortical cells

17. www.cilr.uq.edu.au 2-4 mm 7. The nodule grows

18. www.cilr.uq.edu.au rootnodule Rhizobia (green marker) 100  m 8. Fully functional nodule

19. www.cilr.uq.edu.au Nodulation Timeline Inoculation (day 0) Roots 1-2 days post inoculation (dpi) 4 dpi 4-6 dpi 10 dpi3 weeks pi

20. www.cilr.uq.edu.au Chemical Signals Nodulation involved chemical signals Released by both the Legume plant and the Rhizobium bacteria Nod Factors Flavones

21. www.cilr.uq.edu.au

22. Flavones and Isoflavones Released by Legume roots Signal Rhizobia in the soil that a Legume is present and ready to nodulate Soybean releases Genistein, an isoflavone

23. www.cilr.uq.edu.au Flavones and Isoflavones Flavonoids in Root tip and Thickened root

24. www.cilr.uq.edu.au Nod Factors Rhizobia in response to flavones release Nod factors Nod factors are sugars with specific signalling functions Nod factors signal to a legume that Rhizobia are present in the soil and ready to live in nodules

25. www.cilr.uq.edu.au Nod Factors Each Rhizobum species releases unique Nod factors All Nod factors have a concerved backbone Difference is in the decorations (R 1 R 2 R 3 R 4 R 5 ) and number (n) of sugar repeats

26. www.cilr.uq.edu.au Nod Factor Receptors Each legume species has receptors specific to a unique Nod factor Therefore each legume species nodulates with its own Rhizobium Soybean -Bradyrhizobium japonicum Lotus – Mesorhizobium loti General – Rhizobium NGR234

27. www.cilr.uq.edu.au University of Queensland Australian National University University of Melbourne University of Newcastle CILR

28. www.cilr.uq.edu.au CILR ARC Centre of Excellence for Integrative Legume Research Contact Us HQ: University of Queensland Tel: 3365 3550 Email: director.CILR@uq.edu.au lisette.pregelj@uq.edu.au Visit Our Website! www.cilr.uq.edu.au

29. Picture and Diagram Credits Uli Mathesius Mark Kinkema Peter Gresshoff Dana Hoffmann Michael Sheahan Sureeporn (Ning) Nontachaiyapoom Paul Scott Brett Ferguson