Mechanism of Infection Thread Elongation in Root Hairs ofMedicago truncatulaand Dynamic Interplay with Associated Rhizobial Colonization
Open Access
- 17 October 2008
- journal article
- Published by Oxford University Press (OUP) in Plant Physiology
- Vol. 148 (4), 1985-1995
- https://doi.org/10.1104/pp.108.125674
Abstract
In temperate legumes, endosymbiotic nitrogen-fixing rhizobia gain access to inner root tissues via a specialized transcellular apoplastic compartment known as the infection thread (IT). To study IT development in living root hairs, a protocol has been established for Medicago truncatula that allows confocal microscopic observations of the intracellular dynamics associated with IT growth. Fluorescent labeling of both the IT envelope (AtPIP2;1-green fluorescent protein) and the host endoplasmic reticulum (green fluorescent protein-HDEL) has revealed that IT growth is a fundamentally discontinuous process and that the variable rate of root hair invagination is reflected in changes in the host cell cytoarchitecture. The concomitant use of fluorescently labeled Sinorhizobium meliloti has further revealed that a bacteria-free zone is frequently present at the growing tip of the IT, thus indicating that bacterial contact is not essential for thread progression. Finally, these in vivo studies have shown that gaps within the bacterial file are a common feature during the early stages of IT development, and that segments of the file are able to slide collectively down the thread. Taken together, these observations lead us to propose that (1) IT growth involves a host-driven cellular mechanism analogous to that described for intracellular infection by arbuscular mycorrhizal fungi; (2) the non-regular growth of the thread is a consequence of the rate-limiting colonization by the infecting rhizobia; and (3) bacterial colonization involves a combination of bacterial cell division and sliding movement within the extracellular matrix of the apoplastic compartment.Keywords
This publication has 39 references indexed in Scilit:
- Coordinating Nodule Morphogenesis with Rhizobial Infection in LegumesAnnual Review of Plant Biology, 2008
- Prepenetration Apparatus Assembly Precedes and Predicts the Colonization Patterns of Arbuscular Mycorrhizal Fungi within the Root Cortex of BothMedicago truncatulaandDaucus carotaPlant Cell, 2008
- How rhizobial symbionts invade plants: the Sinorhizobium–Medicago modelNature Reviews Microbiology, 2007
- Medicago LYK3, an Entry Receptor in Rhizobial Nodulation Factor SignalingPlant Physiology, 2007
- Nod Factor Perception During Infection Thread Growth Fine-Tunes NodulationMolecular Plant-Microbe Interactions®, 2007
- LysM Domain Receptor Kinases Regulating Rhizobial Nod Factor-Induced InfectionScience, 2003
- Agrobacterium rhizogenes-Transformed Roots of Medicago truncatula for the Study of Nitrogen-Fixing and Endomycorrhizal Symbiotic AssociationsMolecular Plant-Microbe Interactions®, 2001
- Intracellular accommodation of microbes by plants: a common developmental program for symbiosis and disease?Current Opinion in Plant Biology, 2000
- Rhizobium meliloti lipooligosaccharide nodulation factors: different structural requirements for bacterial entry into target root hair cells and induction of plant symbiotic developmental responses.Plant Cell, 1994
- The Infection of Clover Root Hairs by Nodule Bacteria Studied by a Simple Glass Slide TechniqueMicrobiology, 1957