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    Topic review

    Root Invasion by Ralstonia solanacearum

    Subjects: Plant Sciences
    View times: 136
    Submitted by: Alberto Macho

    Definition

    The plant pathogenic bacterium Ralstonia solanacearum, causal agent of the devastating bacterial wilt disease, is a soil-borne microbe that infects host plants through their roots. The initial mutual recognition between host plants and bacteria and the ensuing invasion of root tissues by R. solanacearum are critical steps in the establishment of the infection, and can determine the outcome of the interaction between plant and pathogen.

    1. Introduction

    Ralstonia solanacearum is one of the top ten plant pathogenic bacteria worldwide according to its scientific and economic importance [1]R. solanacearum is the causal agent of bacterial wilt disease in more than 250 plant species, including agriculturally important crops such as tomato, potato, banana, and peanut [1][2], and can also infect model plants, such as Arabidopsis thaliana (hereafter, Arabidopsis) and Medicago truncatula [1]. As a soil-borne pathogen, R. solanacearum enters plants through the root, using wounds, root tips, and secondary root emerging points as penetration sites; it then progresses via the root cortex, finally reaching the vascular system [3][4][5], as shown in Figure 1. From this point onwards, and mostly through xylem vessels, the infection spreads systemically in the plant [5][6]. The invading bacteria multiply massively in the xylem and produce abundant exopolysaccharides (EPSs), which ultimately leads to the obstruction of the vessels and the subsequent development of the typical wilting symptoms due to impaired water conductance [7].

    Figure 1. Plant invasion by the pathogenic bacterium Ralstonia solanacearum. (A). In the first stage of invasion, bacteria (depicted as yellow circles) enter roots through wounds, emerging lateral roots, and root tips. (B). Schematic representation of a cross-section of a root; different cell types are indicated. In the second stage of invasion, bacteria massively multiply in the intercellular spaces between cortex cells (blue arrows), and cause plasmolysis of epidermal cells. (C). In the last stage of invasion, bacteria (depicted as yellow circles) move throughout the plant through xylem vessels, causing clogging of the vascular system and the typical wilting symptoms. Bacterial movement is depicted as black arrows.

    2. Development

    R. solanacearum is a devastating pathogen with a dramatic economic impact worldwide. Gaining a deeper understanding of the molecular and physiological mechanisms underlying the pathogenicity of this bacterial species is a necessary stepping stone in the design of effective and durable strategies for crop protection in order to guarantee food security. Considering that R. solanacearum is present in the soil, the initial recognition between host plants and bacteria and the ensuing invasion of root tissues are crucial steps in the establishment of the disease, and as such deserve special attention. In this minireview, we will focus on the early stages of the bacterial infection, providing an overview of the defence mechanisms deployed by the host plants upon recognition of the bacteria, of the manipulation exerted by the pathogen in order to promote its own multiplication and spread, and of the developmental changes occurring in the root system during bacterial colonization.

    The entry is from 10.3390/plants9040516

    References

    1. Mansfield, J.; Genin, S.; Magori, S.; Citovsky, V.; Sriariyanum, M.; Ronald, P.; Dow, M.; Verdier, V.; Beer, S.V.; Machado, M.A.; et al. Top 10 plant pathogenic bacteria in molecular plant pathology. Mol. Plant Pathol. 2012, 13, 614–629.
    2. Genin, S. Molecular traits controlling host range and adaptation to plants in Ralstonia solanacearum. New Phytol. 2010, 187, 920–928.
    3. Vasse, J.; Pascal, F.; Trigalet, A. Microscopic studies of intercellular infection and protoxylem invasion of tomato roots by Pseudomonas solanacearum. Mol. Plant-Microbe Interact. 1995, 8, 241–251.
    4. Vailleau, F.; Sartorel, E.; Jardinaud, M.-F.; Chardon, F.; Genin, S.; Huguet, T.; Gentzbittel, L.; Petitprez, M. Characterization of the interaction between the bacterial wilt pathogen Ralstonia solanacearum and the model legume plant Medicago truncatula. Mol. Plant-Microbe Interact. 2007, 20, 159–167.
    5. Digonnet, C.; Martinez, Y.; Denancé, N.; Chasseray, M.; Dabos, P.; Ranocha, P.; Marco, Y.; Jauneau, A.; Goffner, D. Deciphering the route of Ralstonia solanacearum colonization in Arabidopsis thaliana roots during a compatible interaction: Focus at the plant cell wall. Planta 2012, 236, 1419–1431.
    6. Turner, M.; Jauneau, A.; Genin, S.; Tavella, M.-J.; Vailleau, F.; Gentzbittel, L.; Jardinaud, M.-F. Dissection of bacterial wilt on Medicago truncatula revealed two type III secretion system effectors acting on root infection process and disease development. Plant Physiol. 2009, 150, 1713–1722.
    7. Saile, E.; McGarvey, J.A.; Schell, M.A.; Denny, T.P. Role of extracellular polysaccharide and endoglucanase in root invasion and colonization of tomato plants by Ralstonia solanacearum. Phytopathology 1997, 87, 1264–1271.
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