The Bacterial Pathogen Xylella fastidiosa Affects the Leaf Ionome of Plant Hosts during Infection

Abstract

Xylella fastidiosa is a plant pathogenic bacterium that lives inside the host xylem vessels, where it forms biofilm believed to be responsible for disrupting the passage of water and nutrients. Here, Nicotiana tabacum was infected with X. fastidiosa, and the spatial and temporal changes in the whole-leaf ionome (i.e. the mineral and trace element composition) were measured as the host plant transitioned from healthy to diseased physiological status. The elemental composition of leaves was used as an indicator of the physiological changes in the host at a specific time and relative position during plant development. Bacterial infection was found to cause significant increases in concentrations of calcium prior to the appearance of symptoms and decreases in concentrations of phosphorous after symptoms appeared. Field-collected leaves from multiple varieties of grape, blueberry, and pecan plants grown in different locations over a four-year period in the Southeastern US showed the same alterations in Ca and P. This descriptive ionomics approach characterizes the existence of a mineral element-based response to X. fastidiosa using a model system suitable for further manipulation to uncover additional details of the role of mineral elements during plant-pathogen interactions. This is the first report on the dynamics of changes in the ionome of the host plant throughout the process of infection by a pathogen.

Natural Competence Rates Are Variable Among Xylella fastidiosa Strains and Homologous Recombination Occurs In Vitro Between Subspecies fastidiosa and multiplex

“…fastidiosa, sandyi, morus, multiplex, and pauca. The disease mechanism, although not fully understood, involves formation of biofilm in the xylem vessels of host plants and obstruction of xylem sap transport leading to alteration of water and mineral nutrients in aerial plant parts (Chatterjee et al 2008;De La Fuente et al 2013). X. fastidiosa strains are vectortransmitted by xylem sap-feeding insects such as sharpshooters and spittlebugs (Redak et al 2004).…”

Response of Xylella fastidiosa to Zinc: Decreased Culturability, Increased Exopolysaccharide Production, and Formation of Resilient Biofilms under Flow Conditions

“…Some authors have reported Zn deficiencies in X. fastidiosa-infected citrus leaves (11), whereas others have reported increased Zn levels in chlorotic areas of infected citrus leaves (9). Moreover, recent studies by our group show that infection with X. fastidiosa does not cause significant changes in the levels of Zn in hosts (7). Likewise, in vitro studies of the effect of Zn on X. fastidiosa have produced contradictory results: while supplementation of synthetic medium with Zn reduces the growth of X. fastidiosa (12,13), Zn concentrations in xylem vessels have been positively (14) or negatively (15,16) correlated with growth of X. fastidiosa.…”

“…Two hundred microliters of the suspension was used directly for DNA extraction (three replicates) using a modified cetyltrimethylammonium bromide (CTAB) protocol (29), 200 l was treated with ethidium moanoazide (EMA) (30) and subsequently used for DNA extraction (three replicates), and 100 l of the appropriate suspension dilution was plated on PW agar plates (two replicates), prior to a repeated homogenization step, and incubated at 28°C for 2 weeks for enumeration of CFU. For the planktonic phase, a 1.5-ml aliquot was collected and treated in the same manner as the biofilm at each time point (3,5,7, and 10 days p.i.). Three biological replicates were used per treatment, and two independent experiments were performed.…”

“…Recent evidence has shown that, though X. fastidiosa indeed induces water stress, this is only part of the physiological changes the bacterium produces in the susceptible host (6). In addition to changes in water balance, X. fastidiosa infection also alters nutrient uptake in infected plant hosts (6,7). Changes in the levels of Ca, K, P, and other minerals have been found in the leaves of diseased plants compared to control plants (5,(7)(8)(9).…”

“…In addition to changes in water balance, X. fastidiosa infection also alters nutrient uptake in infected plant hosts (6,7). Changes in the levels of Ca, K, P, and other minerals have been found in the leaves of diseased plants compared to control plants (5,(7)(8)(9). Furthermore, interveinal chlorosis produced by X. fastidiosa infection resembles Fe or Zn deficiency in grape and citrus, respectively (10); however, the effects of X. fastidiosa infection on Zn levels in plant tissues are not well defined.…”