Burkholderia phytofirmans Inoculation-Induced Changes on the Shoot Cell Anatomy and Iron Accumulation Reveal Novel Components of Arabidopsis-Endophyte Interaction that Can Benefit Downstream Biomass Deconstruction.

Shuai Zhao,Michael E Himmel,Yining Zeng,Chien-Yuan Lin,Shi-You Ding,Hui Wei,Melvin P Tucker

doi:10.3389/fpls.2016.00024

Shuai Zhao, Michael E Himmel + Show 5 more

Open Access

https://doi.org/10.3389/fpls.2016.00024

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Abstract

It is known that plant growth promoting bacteria (PGPB) elicit positive effects on plant growth and biomass yield. However, the actual mechanism behind the plant-PGPB interaction is poorly understood, and the literature is scarce regarding the thermochemical pretreatability and enzymatic degradability of biomass derived from PGPB-inoculated plants. Most recent transcriptional analyses of PGPB strain Burkholderia phytofirmans PsJN inoculating potato in literature and Arabidopsis in our present study have revealed the expression of genes for ferritin and the biosynthesis and transport of siderophores (i.e., the molecules with high affinity for iron), respectively. The expression of such genes in the shoots of PsJN-inoculated plants prompted us to propose that PsJN-inoculation can improve the host plant's iron uptake and accumulation, which facilitates the downstream plant biomass pretreatment and conversion to simple sugars. In this study, we employed B. phytofirmans PsJN to inoculate the Arabidopsis thaliana plants, and conducted the first investigation for its effects on the biomass yield, the anatomical organization of stems, the iron accumulation, and the pretreatment and enzymatic hydrolysis of harvested biomass. The results showed that the strain PsJN stimulated plant growth in the earlier period of plant development and enlarged the cell size of stem piths, and it also indeed enhanced the essential metals uptake and accumulation in host plants. Moreover, we found that the PsJN-inoculated plant biomass released more glucose and xylose after hot water pretreatment and subsequent co-saccharification, which provided a novel insight into development of lignocellulosic biofuels from renewable biomass resources.

Highlights

The global rise in energy consumption portends an increase in our future energy demands
In addition to the above set of B. phytofirmans genes expressed in PsJN-colonized potato shoot tissues, special efforts were made in this study to identify the gene encoding L-ornithine 5-monooxygenase (EC 1.14.13.195), which catalyzes the conversion of L-ornithine to N5-hydroxyornithine, the first step in the biosynthesis of all hydroxamate-containing siderophores, such as pyoverdin
Previous literature had demonstrated that the L-ornithine 5monooxygenase gene in B. pseudomallei (BPSL1776) is involved in the biosynthesis of siderophore (Alice et al, 2006)

Summary

Introduction

The global rise in energy consumption portends an increase in our future energy demands. It is urgent to develop efficient, sustainable and green energy production systems and biofuels is a leading technology in this field. Biofuels can be broadly categorized as first- and second-generation fuels that are derived from plant grains and oils, and lignocellulosic biomass, respectively (Chaturvedi and Verma, 2013). Grain-based bioethanol production (a first-generation biofuel) is in question because it generates a dilemma over the use of agricultural crops and/or land for fuel vs human food. Lignocellulosic biomass feedstocks (for the second-generation biofuel) are attractive because the human food concern is avoided and it is relatively low cost and sustainable (Agbor et al, 2011). To better meet the rapid increase in energy demands and more efficient utilization of restricted land, it is necessary to rapidly harvest more lignocellulosic biomass per unit time and/or area

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