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Lipopolysaccharides (LPS) are among the known pathogen-associated molecular patterns (PAMPs). LPSs are potent elicitors of PAMP-triggered immunity (PTI), and bacteria have evolved intricate mechanisms to dampen PTI. Here we demonstrate that Xylella fastidiosa (Xf), a hemibiotrophic plant pathogenic bacterium, possesses a long chain O-antigen that enables it to delay initial plant recognition, thereby allowing it to effectively skirt initial elicitation of innate immunity and establish itself in the host. Lack of the O-antigen modifies plant perception of Xf and enables elicitation of hallmarks of PTI, such as ROS production specifically in the plant xylem tissue compartment, a tissue not traditionally considered a spatial location of PTI. To explore translational applications of our findings, we demonstrate that pre-treatment of plants with Xf LPS primes grapevine defenses to confer tolerance to Xf challenge.

No abstract

Pierce's disease (PD) of grapevine is caused by the bacterium Xylella fastidiosa. In this study, an integrated approach was applied to assess PD susceptibility among different Vitis vinifera cultivars that incorporated disease severity, bacterial pathogen abundance and loss of stem xylem hydraulic conductivity. It was hypothesized that levels of PD susceptibility in V. vinifera can be attributed in part to the host anatomical features that are shaped by its pedigree background. Two popular wine grape cultivars were initially selected from the occidentalis group, Merlot and Cabernet Sauvignon, and one from the orientalis group, Thompson Seedless. The more recently bred table grape cultivar Scarlet Royal, that has mixed pedigree parentage, was also included. PD susceptibility was compared to the known PD resistant b43-17 V. arizonica/ candicans wild grape species from North America. The data indicated that Thompson Seedless was ranked as the most susceptible to PD because it significantly exhibited the most severe disease symptoms at 12 weeks post-inoculation and hosted the highest X. fastidiosa titre of the cultivars, and lost over 90% of its stem hydraulic conductivity. In contrast, the other three cultivars displayed less susceptibility to PD. The way in which the xylem anatomy could impact PD susceptibility in V. vinifera cultivars is discussed, together with how grape pedigrees and their cognate centre of domestication may have influenced xylem anatomical features. This work provides a reference framework to further test the hypothesis that V. vinifera cultivars with wide xylem vessels may be more prone to PD decline.

Pierce's disease of grapevine and citrus huanglongbing are caused by the bacterial pathogens Xylella fastidiosa and Candidatus Liberibacter asiaticus (CLas), respectively. Both pathogens reside within the plant vascular system, occluding water and nutrient transport, leading to a decrease in productivity and fruit marketability and ultimately death of their hosts. Field observations of apparently healthy plants in disease-affected vineyards and groves led to the hypothesis that natural products from endophytes may inhibit these bacterial pathogens. Previously, we showed that the natural product radicinin from Cochliobolus sp. inhibits X. fastidiosa. Herein we describe a chemical synthesis of deoxyradicinin and establish it as an inhibitor of both X. fastidiosa and Liberibacter crescens, a culturable surrogate for CLas. The key to this three-step route is a zinc-mediated enolate C-acylation, which allows for direct introduction of the propenyl side chain without extraneous redox manipulations. P ierce's disease of grapevine and citrus huanglongbing (also known as citrus greening) are devastating plant diseases threatening important US agricultural industries. Both are caused by Gram-negative bacterial pathogens, spread by way of insect vectors. Pierce's disease, known in California since the 1800s, is caused by the bacterium Xylella fastidiosa, which inhabits the xylem of the plant. 1−3 As bacteria levels increase, the xylem becomes blocked and the flow of water and nutrients from the roots to the leaves is impeded, resulting in discolored and dried leaves, shriveled fruit, and stunted vine growth, ultimately leading to vine death. 4−6 X. fastidiosa is transmitted by xylem-feeding insects commonly known as leafhoppers. Native leafhoppers are limited in their flight range and transmission efficiency, and until recently, Pierce's disease outbreaks remained mostly isolated to small areas at a time. However, in 1989, an especially effective insect vector, the glassy-winged sharpshooter, was introduced to Southern California. The glassy-winged sharpshooter has infested most of Southern California, including the Malibu, Temecula Valley, and San Diego wine regions, and has made its way north into the Central Valley, posing an imminent threat to the California wine, raisin, and table grape industries.Huanglongbing is caused by the unculturable bacterium Candidatus Liberibacter asiaticus (CLas). 7−9 Unlike X. fastidiosa, CLas colonizes the phloem (food transport tissue) of citrus trees. Huanglongbing-infected trees experience root loss, dieback, starch buildup, and mottled yellow leaves. 10,11 Affected fruit are often green, stunted, and bitter and may drop prematurely. 12,13 Huanglongbing can drastically impact the yield productivity of a tree and can ultimately prove fatal. CLas