Browsing by Author "Marshall Bergen"

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Bacterial endophytes from rice cut grass (Leersia oryzoides L.) increase growth, promote root gravitropic response, stimulate root hair formation, and protect rice seedlings from disease
(Springer International Publishing, 2018) Satish K. Verma; Kathryn Kingsley; Marshall Bergen; Camille English; Matthew Elmore; Ravindra N. Kharwar; James F. White
Background and Aims: Leersia oryzoides, a wild relative of rice (Oryza sativa), may carry potential seed-borne bacterial endophytes which could be used to enhance growth of rice. We hypothesized that seed-associated bacteria from L. oryzoides would be compatible with rice and promote seedling growth, development, and survival. Methods: We isolated bacteria from seed of L. oryzoides and checked compatibility with rice as well as Bermuda grass seeds for seedling growth promotion. Internal colonisation of bacteria into root cells was observed by ROS staining and microscopic observation. Growth promoting bacteria were evaluated for IAA production, phosphate solubilization and antifungal activities. Results: Overall, ten bacteria were found to be growth promoting in rice seedlings with effects including restoration of root gravitropic response, increased root and shoot growth, and stimulation of root hair formation. All bacteria were identified by 16S rDNA sequencing. Six bacteria were found to become intracellular in root parenchyma and root hairs in rice and in Bermuda grass seedlings. Six bacteria were able to produce IAA in LB broth with highest (47.06 ± 1.99 μg ml−1) by LTE3 (Pantoea hericii). Nine isolates solubilized phosphate and inhibited at least one soil borne fungal pathogen. Conclusions: Seed bacteria of L. oryzoides are compatible with rice. Many of these bacteria become intracellular, induce root gravitropic response, increase root and shoot growth, and stimulate root hair formation in both rice and Bermuda grass seedlings. Presence of bacteria protects seedlings from soil pathogens during seedling establishment. This research suggests that bioprospecting microbes on near relatives of rice and other crop plants may be a viable strategy to obtain microbes to improve cultivation of crops. © 2017, Springer International Publishing AG.
Reactive Oxygen Defense Against Cellular Endoparasites and the Origin of Eukaryotes
(Elsevier, 2018) James F. White; Kathryn Kingsley; Carla J. Harper; Satish K. Verma; Lara Brindisi; Qiang Chen; Xiaoqian Chang; April Micci; Marshall Bergen
In this chapter, we propose a model for the early evolution of eukaryotic cells under pressure of intense endoparasitism. We define features of eukaryotes developed to defend against endoparasites (primarily bacteria), including a defensive system composed of an antioxidant sterol-enriched internal and external membrane system that could be used to entrap endoparasites and degrade them with superoxide produced on the membranes, cytoskeleton scaffolding for the membrane system, and a nuclear envelope to exclude endoparasites from reaching the genome. Mitochondria and chloroplasts evolved from the prokaryotes that developed ways to neutralize the reactive oxygen defense of the host. For mitochondria, hydrogen pumping to the exterior of the endoparasite enabled them to reduce superoxide to water, effectively defeating the host defense. Other features of eukaryotes that may have evolved from defense from endoparasitism include: autophagy, cell walls in fungi and plants, acquired immunity in animals, multicellularity, and apoptosis. We evaluate fossil data, where available, to provide additional information regarding the early evolution of eukaryotes and the prevalence of endoparasitic microbes. © 2018 Elsevier Inc. All rights reserved.