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Conservation in Function of a SCAR/WAVE Component During Infection Thread and Root Hair Growth in Medicago truncatula

December 2010 , Volume 23 , Number  12
Pages  1,553 - 1,562

Akira Miyahara,1 Jennifer Richens,1 Colby Starker,2 Giulia Morieri,3 Lucinda Smith,2 Sharon Long,2 J. Allan Downie,3 and Giles E. D. Oldroyd1

1Department of Disease and Stress Biology, John Innes Centre, Norwich Research Park, Colney Lane, Norwich, NR4 7UH, U.K.; 2Department of Biological Sciences, Stanford University, Stanford, CA 94305, U.S.A.; 3Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Colney Lane, Norwich, NR4 7UH, U.K.

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Accepted 7 August 2010.

Nitrogen-fixing symbioses of plants are often associated with bacterially infected nodules where nitrogen fixation occurs. The plant host facilitates bacterial infection with the formation of infection threads, unique structures associated with these symbioses, which are invaginations of the host cell with the capability of traversing cellular junctions. Here, we show that the infection thread shares mechanistic similarities to polar-growing cells, because the required for infection thread (RIT) locus of Medicago truncatula has roles in root-hair, trichome, and infection-thread growth. We show that RIT encodes the M. truncatula ortholog of NAP1, a component of the SCAR/WAVE (suppressor of cAMP receptor/WASP-family verprolin homologous protein) complex that regulates actin polymerization, through the activation of ARP2/3. NAP1 of Arabidopsis thaliana functions equivalently to the M. truncatula gene, indicating that the mode of action of NAP1 is functionally conserved across species and that legumes have not evolved a unique functionality for NAP1 during rhizobial colonization. This work highlights the surprising commonality between polar-growing cells and a polar-growing cellular intrusion and reveals important insights into the formation and maintenance of infection-thread development.

© 2010 The American Phytopathological Society