Endophytic Colonization of Vitis vinifera L. by Plant Growth-Promoting Bacterium Burkholderia sp. Strain PsJN

Abstract

Patterns of colonization of Vitis vinifera L. cv. Chardonnay plantlets by a plant growth-promoting bacterium, Burkholderia sp. strain PsJN, were studied under gnotobiotic conditions. Wild-type strain PsJN and genetically engineered derivatives of this strain tagged with gfp (PsJN::gfp2x) or gusA (PsJN::gusA11) genes were used to enumerate and visualize tissue colonization. The rhizospheres of 4-to 5-week-old plantlets with five developed leaves were inoculated with bacterial suspensions. Epiphytic and endophytic colonization patterns were then monitored by dilution plating assays and microscopic observation of organ sections. Bacteria were chronologically detected first on root surfaces, then in root internal tissues, and finally in the fifth internode and the tissues of the fifth leaf. Analysis of the PsJN colonization patterns showed that this strain colonizes grapevine root surfaces, as well as cell walls and the whole surface of some rhizodermal cells. Cells were also abundant at lateral root emergence sites and root tips. Furthermore, cell wall-degrading endoglucanase and endopolygalacturonase secreted by PsJN explained how the bacterium gains entry into root internal tissues. Host defense reactions were observed in the exodermis and in several cortical cell layers. Bacteria were not observed on stem and leaf surfaces but were found in xylem vessels of the fifth internode and the fifth leaf of plantlets. Moreover, bacteria were more abundant in the fifth leaf than in the fifth internode and were found in substomatal chambers. Thus, it seems that Burkholderia sp. strain PsJN induces a local host defense reaction and systemically spreads to aerial parts through the transpiration stream.

Non-pathogenic Rhizobium radiobacter F4 deploys plant beneficial activity independent of its host Piriformospora indica

“…At a later time point (21 dpi), RrF4 also colonized the sites of secondary root emergence. Cracks at secondary root emergence sites may be used by RrF4 for passive entrance into the inner root tissue as was suggested for several endophytic bacteria (Reinhold-Hurek and Hurek, 1998;Compant et al, 2005). In contrast to barley, the central vascular system (xylem) of primary (Figures 6d and e) and secondary roots (data not shown) were heavily colonized.…”

“…The non-pathogenic R. radiobacter F4 SP Glaeser et al Larger cell aggregates (micro-colonies) often developed at the sites of root hair protrusion rather than being attached to fully developed root hairs (Figures 4e and f). Root hair protrusion sides serve as bacterial entrance into the inner root tissue (Compant et al, 2005). TEM showed a detailed picture of the approximately 5-μm-thick multilayer biofilm with RrF4 cells embedded by a dense matrix of extracellular polymeric substances (Figure 4g).…”

The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

“…Second, many rhizosphere microorganisms can induce a systemic response in the plant, resulting in the activation of plant defence mechanisms (Pieterse et al 2003). This capacity has been identified in a wide range of bacteria (Van Loon et al 1998;Haas and Défago 2005), including endophytes (Compant et al 2005) as well as saprophytic (Fuchs et al 1997), hyperparasitic (Woo et al 2006) and arbuscular mycorrhizal fungi (Pozo et al 2002). Induced systemic resistance (ISR) does not confer complete protection, but it does protect the plant from various types of phytopathogens (including root pathogens), without requiring direct interaction between the resistance-inducing microorganisms and the pathogen (Van Loon et al 1998;Zehnder et al 2001).…”

Endophytic colonization of rice (Oryza sativa L.) by the diazotrophic bacterium Burkholderia kururiensis and its ability to enhance plant growth

“…Further studies on sequence comparisons of amplified polymerase chain reaction glnB, nifH, and 16S rDNA gene fragments of nitrogen-fixing Burkholderia species suggested a close phylogenetic and functional relationship between B. kururiensis and "B. brasilensis" (Marin et al 2003); nevertheless, "B. brasilensis" is a species not officially validated (Caballero-Mellado et al 2007). Therefore, a detailed investigation of a putative B. kururiensisplant association is of great interest, specially with rice, which is one the most important staple crop in the developing world (Barraquio et al 1997, Kuklinsky-Sobral et al 2004, since many studies have been focused on the search for natural diazotrophs that can possibly act as plant-growth promoting associative bacteria (Baldani et al 2000, Biswas et al 2000, Trân Van et al 2000, Ciccillo et al 2002, Compant et al 2005, Muthukumarasamy et al 2006, Rosenblueth and Martinez-Romero 2006, Govindarajan et al 2008). …”