ARC Centre of Excellence for Integrative Legume Research

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

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

www. cilr. uq. edu. au

Vascular Bundles Nodule Cortex Sclerenchyma Rhizobium Filled Cells >25, 000 per cell Nodule Cross-Section 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 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 www. cilr. uq. edu. au

1: Rhizobia attracted to root 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 www. cilr. uq. edu. au Bacteria turn blue when a reporter gene is switched on by plant exudates (flavonoids)

2. Rhizobia attach to root hairs Rhizobia Root Hair 10 mm www. cilr. uq. edu. au

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

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

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

4. Rhizobia infect root hair 50 mm www. cilr. uq. edu. au

5. Root cortical cells divide 100 mm www. cilr. uq. edu. au

5. Root cortical cells divide 100 mm www. cilr. uq. edu. au

6. Rhizobia invade cortical cells 50 mm www. cilr. uq. edu. au

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

8. Fully functional nodule root nodule Rhizobia (green marker) 100 mm www. cilr. uq. edu. au

Nodulation Timeline Roots Inoculation (day 0) 4 -6 dpi 1 -2 days post inoculation (dpi) 10 dpi www. cilr. uq. edu. au 4 dpi 3 weeks pi

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

www. cilr. uq. edu. au

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 www. cilr. uq. edu. au

Flavones and Isoflavones Flavonoids in Root tip and Thickened root 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 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 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 NGR 234 www. cilr. uq. edu. au

CILR • University of Queensland • Australian National University • University of Melbourne • University of Newcastle 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

Picture and Diagram Credits • • Uli Mathesius Mark Kinkema Peter Gresshoff Dana Hoffmann Michael Sheahan Sureeporn (Ning) Nontachaiyapoom Paul Scott Brett Ferguson www. cilr. uq. edu. au