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James White

Professor, Dept. of Plant Biology

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Rhizophagy cycle endophytes

We are working to develop an understanding of rhizophagy cycle in turf grasses. The rhizophagy cycle is a new kind of symbiosis whereby plants obtain nutrients from bacteria that alternate between an intracellular/endophytic phase and a free-living soil phase. Bacteria acquire soil nutrients in the free-living soil phase; nutrients are extracted from bacteria oxidatively in the intracellular/endophytic phase. This process for nutrient extraction from microbes appears to be important in grasses and much of the experimental work involves use of turfgrass systems. There is some indication that beneficial endophytes in turf grasses may be those bacteria that are adapted to plants and participate in the rhizophagy cycle, delivering nutrients from soils; endophytes that are not beneficial in turf grasses may be those bacteria that are not adapted for the rhizophagy symbiosis and do not carry nutrients into plants.

Bioherbicidal microbes

In collaboration with Dr. Matt Elmore we are examining ways to control weeds by inhibiting the symbiosis of the weed with endophytic microbes. We have identified microbial endophytes that may be used to promote turf grass growth (and other crops), but that will simultaneously inhibit competitor weed growth. Our goal is to use endophytes to replace herbicides in turf grass systems.

More About James White
The rhizophagy cycle. Figure from Microorganisms 6 (3): 95. (2018).
Figure 1: Diagrammatic representation of the rhizophagy cycle. 1A. Diagram of the rhizophagy cycle showing microbes entering root cells at the root tip meristem and exiting root cells at the tips of elongating root hairs. Rhizophagy cycle microbes alternate between an intracellular endophytic phase and a free-living soils phase; soil nutrients are acquired in the free-living soil phase and extracted oxidatively in the intracellular endophytic phase. 1B. Shows bacteria (arrow) in the periplasmic space of parenchyma cell near root tip meristem of an Agave sp. seedling (bar = 20 µm; stained with DAB followed by aniline blue). 1C. Bacteria (arrow) emerging from root hair tip of grass seedling (bar = 20 µm; stained with fluorescent nucleic stain SYTO 9).
Microbes in plant roots.
Figures 2-5: Microbes in plant roots. 2. Cloud of bacteria (arrows) around root tip meristem of invasive reed grass (Phragmites australis); stained with aniline blue (0.1% aqueous). 3. Root parenchyma cell of P. australis showing replicating protoplasts of bacteria (arrows) in the periplasmic space of the cell (stained with DAB, followed by aniline blue; bar = 15 µ). 4. Root hair of grass Cynodon dactylon inoculated with bacterium Pseudomonas sp. showing bacterial protoplasts (arrows) in the periplasmic space of the hair (stained with DAB, followed by aniline blue; bar = 15 µ). 5. Root hairs of clover (Trifolium repens) inoculated with endophytic yeast (Rhodotorula sp.) showing yeast being expelled from the root hair tips (black arrows) and yeast protoplasts within root hairs (white arrow)(stained with DAB, followed by aniline blue; bar = 15 µ).
Nutrient mining by rhizophagy microbes.
Figure 6: Diagrammatic representation of nutrient mining by rhizophagy microbes. Plant roots secrete organic acids (citric, malic, and acetic acids) into the soil. Organic acids complex with metals in the soil (Fe3+, Mg2+, Co2+, Mn2+, Co2+, Cu2+, Ni2, etc…). Rhizophagy cycle microbes possess transporters that bind to these organic acid-metal complexes and absorb them into the microbe cells. Microbes then return to the plant root and enter into root cells where nutrients are extracted from microbes oxidatively.