De La Fuente Lab

Calcium regulation of interactions between a xylem-inhabiting pathogenic bacterium and host plants

The bacterium Xylella fastidiosa causes destructive diseases in crops such as grapes, citrus, blueberries and others. These diseases are found mainly in the Americas, but there have been recent reports of this bacterium causing problems in Asia and Europe. This bacterium, transmitted among plants by insect vectors, lives inside the xylem vessels, which are the components of the vascular system of the plant involved in transporting water and mineral nutrients from the soil to the rest of the plant. Inside the xylem the bacterium forms biofilms, or agglomerates of bacteria surrounded by a sticky matrix, that clogs the passage of nutrients in the plant and is believed to be responsible for the development of symptoms. Currently there is no cure for the diseases caused by Xylella fastidiosa, and infected plants need to be removed and discarded.

Our research has shown that one particular mineral element, calcium, has an important role during the disease development, by increasing the virulence of the bacterium, and being accumulated in infected plants. Our data indicates that the plant defense response to infection may worsen the disease, analogous to what occurs in autoimmune diseases in animals. During this project we will elucidate the key proteins in both plant and bacteria that are involved in the calcium modification occurring during disease. This information will allow us to target those proteins for specific disease control methods.

PROJECT COLLABORATORS:

Paul Cobine and Aaron Rashotte (Department of Biological Sciences, Auburn University)

Mickael Malnoy (Fondazione Edmund Mach)

PROJECT FUNDED BY:

NIFA-AFRI Foundational Program

Transcriptional regulation of calcium among animal and plant pathogenic bacteria studied in a microfluidic model system.

Through an interdisciplinary collaboration among bacterial pathologists working in diverse systems, we will elucidate the molecular basis of the regulatory effect of calcium (Ca2+) on biofilm formation and virulence. Previous work by our groups have identified that Ca2+ regulates virulence traits of bacterial pathogens. To understand the basis of this regulation we will describe the whole transcriptome of plant (Xylella fastidiosa), fish (Flavobacterium columnare) and human (Staphylococcus aureus) pathogens in their response to increasing Ca2+ concentrations. We will study this regulation by establishing a versatile and novel model system utilizing microfluidic chambers (MC). The long term research objective of our team is to test the hypothesis that responses of diverse bacterial pathogens to Ca2+ are regulated by a genetic network that affects virulence. During this research we will identify genes transcriptionally regulated by Ca2+ using an RNA-Seq approach. The long-term applied goal of this research is to develop specific inhibitors for Ca2+-regulated proteins (identified via the proposed research) to use in human, animal, and plant disease management.

PROJECT COLLABORATORS:

Covadonga Arias (School of Fisheries, Aquaculture, and Aquatic Sciences, Auburn University)

Peter Panizzi (Harrison School of Pharmacy, Auburn University)

PROJECT FUNDED BY:

AU-IGP (Auburn University Intramural Grants Program)

The bacterium ‘Candidatus Liberibacter asiaticus’ (LAS) is the suspected causal agent of the disease known as citrus greening (or huanglongbin), affecting citrus production worldwide, especially in Florida (US), Brazil, and China. Culturing LAS in the laboratory by traditional bacterial culture methods is extremely difficult. This has caused a knowledge deficit regarding LAS biology that inhibits the generation of well-informed ideas for pathogen control. We are starting a new project based on the use of a novel methodology which uses microfluidic chambers and microscopic observations to improve the culture conditions of LAS and confirm infection traits and nutritional requirements suggested by the recent full genome sequence.

Project Funded By:

• FCPRAC (Florida Citrus Production Research Advisory Council)

Xylella fastidiosa is a gram negative, xylem-limited plant pathogenic bacterium that causes diseases in many economically important crops worldwide including grape, citrus and olives. Cu as an antimicrobial compound is widely-used in plant diseases control since the 1880’s. Although Cu-containing antimicrobials are not generally used directly in the management of diseases caused by X. fastidiosa, these compounds are widely applied to X. fastidiosa hosts in vineyards and orchards. Cu accumulation in the soils of those fields is relatively high after years of spray, which lead to X. fastidiosa exposure to high Cu concentrations in the xylem. Although the effects of Cu have been extensively studied for foliar pathogen control, it is still unknown what effects Cu has on a xylem-inhabitant pathogen. Previous results from our group showed that Cu influences X. fastidiosa growth in vitro, which includes biofilm formation, and cell-cell adhesion. In this project, our group aims to understand the influence of Cu on X. fastidiosa growth in planta and on its virulence, as well as to unveil the molecular mechanisms of Cu tolerance/resistance in X. fastidiosa.

Pierce’s Disease (PD), caused by Xylella fastidiosa (Xf) has economically affected the California grape industry for over a century. Growers lose an estimated $56 million annually in decreased production and vine replanting. Breeding efforts have resulted in new wine grape cultivars using a single source of PD resistance. This source has been effective against a few strains of Xf, but its durability in the field is unclear. The range in virulence (amount of disease a given isolate can cause) of Xf in California is not known, and regional differences appear likely. Research is being conducted to better understand the variability of Xf in California and how this might impact PD resistant grapes. This proposal will evaluate Xf virulence and the sustainability of PD resistant material.

Funding:

California Department of Food and Agriculture

Collaborators:

Rachel P. Naegele, USDA ARS (USDA-ARS)

https://www.ars.usda.gov/people-locations/person/?person-id=51292

Rodrigo P. P. Almeida (Department of Environmental Science, Policy & Management, UC Berkeley) https://nature.berkeley.edu/almeidalab/