Root Border Cells and Their Role in Plant Defense

Hawes, Martha C.; Allen, Caitilyn; Turgeon, B. Gillian; Curlango‐Rivera, Gilberto; Tran, Tuan Minh; Huskey, David A.; Zhou, Xiong

doi:10.1146/annurev-phyto-080615-100140

Cited by 106 publications

(98 citation statements)

References 117 publications

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“…We also considered other approaches, such as the use of RNAi to silence components of flavonoid exudation machinery and the use of adsorbents to prevent rhizodeposit isoflavonoids from reaching rhizosphere microbes. However, rhizodeposition of isoflavonoids occurs through mechanisms other than root exudation as well, e.g., root border cells (Hawes et al 2000). Therefore, silencing components of root exudation machinery (e.g., ABC transporters [Brechenmacher et al 2009;Sugiyama et al 2007]) might not result in efficient depletion of isoflavonoids in rhizodeposits.…”

Section: Discussionmentioning

confidence: 99%

Spatio Temporal Influence of Isoflavonoids on Bacterial Diversity in the Soybean Rhizosphere

White¹,

Jothibasu²,

Reese³

et al. 2015

MPMI

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High bacterial density and diversity near plant roots has been attributed to rhizodeposit compounds that serve as both energy sources and signal molecules. However, it is unclear if and how specific rhizodeposit compounds influence bacterial diversity. We silenced the biosynthesis of isoflavonoids, a major component of soybean rhizodeposits, using RNA interference in hairy-root composite plants, and examined changes in rhizosphere bacteriome diversity. We used successive sonication to isolate soil fractions from different rhizosphere zones at two different time points and analyzed denaturing gradient gel electrophoresis profiles of 16S ribosomal RNA gene amplicons. Extensive diversity analysis of the resulting spatio temporal profiles of soybean bacterial communities indicated that, indeed, isoflavonoids significantly influenced soybean rhizosphere bacterial diversity. Our results also suggested a temporal gradient effect of rhizodeposit isoflavonoids on the rhizosphere. However, the hairy-root transformation process itself significantly altered rhizosphere bacterial diversity, necessitating appropriate additional controls. Gene silencing in hairy-root composite plants combined with successive sonication is a useful tool to determine the spatio temporal effect of specific rhizodeposit compounds on rhizosphere microbial communities.Pioneering microbiology studies by L. Hiltner in the early 1900s showed that the highest microbial density in soils occurs very close to plant roots (Hinsinger and Marschner 2006). For example, a four-to fivefold increase in CFU was observed in root-surface scrapings as compared with soil samples 0.5 cm away from the roots (Clark 1940). Such changes are attributed to the rich carbon energy sources provided by the plant. Indeed, plants release, on average, 10 to 15% (Jones et al. 2009) of their photosynthetic assimilates into the rhizosphere, a process called rhizodeposition (Dennis et al. 2010). These rhizodeposits originate from sloughed off root border and root border-like cells from root tips, active root exudation, and cell lysis. Rhizodeposits are composed of sugars, amino acids, organic acids, fatty acids, proteins, ions, secondary metabolites, mucilage, water, and miscellaneous carbon-containing compounds (Bais et al. 2006;Dennis et al. 2010).Significant evidence accumulated over the years indicates that the composition of root microbial communities is influenced, in large part, by the plant species and its developmental stage (Micallef et al. 2009;Mougel et al. 2006;Weisskopf et al. 2006). Indeed, an intricate coevolution of plants and rhizosphere microbial communities was suggested by the observation that resident plants or their root exudates are capable of maintaining the biomass and diversity of soil fungal communities to a much greater extent than nonresident or introduced plants ). This is supported by the observation that invasive weeds have the ability to significantly influence native rhizosphere microbial communities to exert their dominance in new environments (Inder...

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Section: Discussionmentioning

confidence: 99%

Spatio Temporal Influence of Isoflavonoids on Bacterial Diversity in the Soybean Rhizosphere

White¹,

Jothibasu²,

Reese³

et al. 2015

MPMI

View full text Add to dashboard Cite

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“…Indeed, crop species had a greater influence on the rhizosphere than model plants, selecting more rhizosphere-specific bacterial OTUs (Supplementary Figures S2k, S5c and S11). This is probably explained by the more extensive root systems of crop plants, leading to increased root exudation and root turnover (Hawes et al, 2000).…”

Section: Microbiota Selection In Compostmentioning

confidence: 99%

Stability and succession of the rhizosphere microbiota depends upon plant type and soil composition

et al. 2015

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We examined succession of the rhizosphere microbiota of three model plants (Arabidopsis, Medicago and Brachypodium) in compost and sand and three crops (Brassica, Pisum and Triticum) in compost alone. We used serial inoculation of 24 independent replicate microcosms over three plant generations for each plant/soil combination. Stochastic variation between replicates was surprisingly weak and by the third generation, replicate microcosms for each plant had communities that were very similar to each other but different to those of other plants or unplanted soil. Microbiota diversity remained high in compost, but declined drastically in sand, with bacterial opportunists and putative autotrophs becoming dominant. These dramatic differences indicate that many microbes cannot thrive on plant exudates alone and presumably also require carbon sources and/or nutrients from soil. Arabidopsis had the weakest influence on its microbiota and in compost replicate microcosms converged on three alternative community compositions rather than a single distinctive community. Organisms selected in rhizospheres can have positive or negative effects. Two abundant bacteria are shown to promote plant growth, but in Brassica the pathogen Olpidium brassicae came to dominate the fungal community. So plants exert strong selection on the rhizosphere microbiota but soil composition is critical to its stability. microbial succession/ plant-microbe interactions/rhizosphere microbiota/selection.

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“…Detaching root cap cells are termed border cells (BCs), because they constitute the border between the root and the soil environment. It has been suggested that BCs mediate plant-rhizosphere interactions by adjusting the physical and chemical properties of the soil and by influencing the microbial flora around the roots (Cannesan et al, 2012;Driouich et al, 2013;Hawes et al, 2000;Vicre et al, 2005). In Arabidopsis, BCs do not detach as individual cells, but rather separate as an organized layer.…”

Section: Introductionmentioning

confidence: 99%

Control of root cap maturation and cell detachment by BEARSKIN transcription factors in Arabidopsis

et al. 2016

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The root cap supports root growth by protecting the root meristem, sensing gravity and interacting with the rhizosphere through metabolite secretion and cell dispersal. Sustained root cap functions therefore rely on balanced proliferation of proximal stem cells and regulated detachment of distal mature cells. Although the gene regulatory network that governs stem cell activity in the root cap has been extensively studied in Arabidopsis, the mechanisms by which root cap cells mature and detach from the root tip are poorly understood. We performed a detailed expression analysis of three regulators of root cap differentiation, SOMBRERO, BEARSKIN1 and BEARSKIN2, and identified their downstream genes. Our results indicate that expression of BEARSKIN1 and BEARSKIN2 is associated with cell positioning on the root surface. We identified a glycosyl hydrolase 28 (GH28) family polygalacturonase (PG) gene as a direct target of BEARSKIN1. Overexpression and loss-of-function analyses demonstrated that the protein encoded by this PG gene facilitates cell detachment. We thus revealed a molecular link between the key regulators of root cap differentiation and the cellular events underlying root cap-specific functions.

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Root Border Cells and Their Role in Plant Defense

Cited by 106 publications

References 117 publications

Spatio Temporal Influence of Isoflavonoids on Bacterial Diversity in the Soybean Rhizosphere

Spatio Temporal Influence of Isoflavonoids on Bacterial Diversity in the Soybean Rhizosphere

Stability and succession of the rhizosphere microbiota depends upon plant type and soil composition

Control of root cap maturation and cell detachment by BEARSKIN transcription factors in Arabidopsis

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