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Summary: Priming is an adaptive mechanism that fortifies plant defense by enhancing activation of induced defense responses following pathogen challenge. Microorganisms have signature microbe‐associated molecular patterns (MAMPs) that induce the primed state. The lipopolysaccharide (LPS) MAMP isolated from the xylem‐limited pathogenic bacterium, Xylella fastidiosa, acts as a priming stimulus in Vitis vinifera grapevines. Grapevines primed with LPS developed significantly less internal tyloses and external disease symptoms than naive vines.Differential gene expression analysis indicated major transcriptomic reprogramming during the priming and postpathogen challenge phases. Furthermore, the number of differentially expressed genes increased temporally and spatially in primed vines, but not in naive vines during the postpathogen challenge phase.Using a weighted gene co‐expression analysis, we determined that primed vines have more genes that are co‐expressed in both local and systemic petioles than naive vines indicating an inherent synchronicity that underlies the systemic response to this vascular pathogen specific to primed plants.We identified a cationic peroxidase, VviCP1, that was upregulated during the priming and postpathogen challenge phases in an LPS‐dependent manner. Transgenic expression of VviCP1 conferred significant disease resistance, thus, demonstrating that grapevine is a robust model for mining and expressing genes linked to defense priming and disease resistance. [ABSTRACT FROM AUTHOR]

Hydraulic failure has been extensively studied during drought-induced plant dieback, but its role in plant-pathogen interactions is under debate. During esca, a grapevine (Vitis vinifera) disease, symptomatic leaves are prone to irreversible hydraulic dysfunctions but little is known about the hydraulic integrity of perennial organs over the short- and long-term. We investigated the effects of esca on stem hydraulic integrity in naturally infected plants within a single season and across season(s). We coupled direct (k s ) and indirect (k th ) hydraulic conductivity measurements, and tylose and vascular pathogen detection with in vivo X-ray microtomography visualizations. Xylem occlusions (tyloses) and subsequent loss of stem hydraulic conductivity (k s ) occurred in all shoots with severe symptoms (apoplexy) and in more than 60% of shoots with moderate symptoms (tiger-stripe), with no tyloses in asymptomatic shoots. In vivo stem observations demonstrated that tyloses occurred only when leaf symptoms appeared, and resulted in more than 50% loss of hydraulic conductance in 40% of symptomatic stems, unrelated to symptom age. The impact of esca on xylem integrity was only seasonal, with no long-term impact of disease history. Our study demonstrated how and to what extent a vascular disease such as esca, affecting xylem integrity, could amplify plant mortality through hydraulic failure. [ABSTRACT FROM AUTHOR]

Morphological traits of the plant vascular system such as xylem vessel diameter have been implicated in many physiological processes including resistance to drought-induced xylem cavitation and vessel occlusion during infection with vascular wilt diseases. In both events, xylem vessels lose function because they become filled with air or tyloses and gels. Xylem cavitation has been well studied, whereas vessel occlusion remains purely descriptive even though it is a critical response to wounding injuries and compartmentalization of vascular pathogens. The timing of vessel occlusion is a key determinant to a successful compartmentalization of pathogens within the plant vascular system and we hypothesized that xylem vessel diameter is the driving variable. Using a dye injection method coupled with automated image analysis, we parameterized a model to investigate how xylem vessel diameter affects the speed of vessel occlusion in Vitis vinifera L. cv. Cabernet Sauvignon in response to wounding. Our dataset contains observations from 6,646 vessels at five kinetic points following stem pruning, over a time course of 1 week. Using this approach we provide evidence that the diameter of vessels is a key determinant of the timing of their occlusion. We discuss how these findings impact resistance to vascular wilt diseases in perennial woody hosts. [ABSTRACT FROM AUTHOR]

Shoot pruning could cause short-term damages to vines. In response to damage, tyloses develop in shoot xylem vessels interfering free water and mineral transportation. In this study, the tylosis development at different nodes of the current-year and perennial shoots of sixty three-year-old grapevines ( Vitis vinifera L.) after pruning was investigated. The results showed that tyloses at the nodes closest to the trunk developed rapidly; and tylosis development initiated at the time when the size of vessel-ray pit was greater than that of parenchyma cell-parenchyma cell pit. In current-year shoots, tyloses were formed in up to 87% of the vessels, and 40% of the vessels were completely blocked by tyloses. In wound-induced perennial shoots, 30% of the vessels were completely blocked by tyloses. When few vessels were blocked by tyloses, new vessels could differentiate, and water transportation system may be restored. However, when tyloses developed in a large number of vessels and the large number of the vessels were blocked, the original capability of water transport was decreased (the largest decrease was 21.1% in this study), resulting in dehiscence or shrinkage cracking in this area. The study proved that the tylosis formation in functional vessels limited the water transport efficiency. [ABSTRACT FROM AUTHOR]

Vascular occlusion in xylem conduits is a common response to environmental stresses, and plant species are recognized as primarily tylose-forming or gel-forming. These stresses occur throughout the year, but there is little information on the wound responses throughout the year and in growing and dormant tissues. Wound-induced vascular occlusions were evaluated by type (tylose or gel), temporal progress, and spatial distribution for grape stems pruned in four seasons through an entire year. Tyloses were formed predominantly in summer and gels in winter. Cytohistological analyses indicated that wound-induced gels were pectin-rich. Both gel formation and tylose development were complete within 7 d and 10 mm from the cut regardless of the season of the wounding. Most vessels were affected by wounding, but a higher fraction of vessels developed occlusions in summer and autumn (over 80%) than in winter and spring (about 60%). The study is the first to show a single species is capable of producing primarily either tyloses or gels and that the type of wound-induced occlusion is dependent upon the season in which wounding occurs. Winter conditions limit the wound response to reversible gel formation that may contribute to refilling of embolized vessels in the spring. [ABSTRACT FROM AUTHOR]

Tyloses form in xylem vessels in response to various environmental stimuli, but little is known of the kinetics or regulation of their development. Preliminary investigations indicated that wounds seal quickly with tyloses after pruning of grapevine shoots. In this study, tylose development was analyzed qualitatively and quantitatively at different depths and times from pruning Cuts along current-year shoots of grapevines at basal, middle, and apical stem regions. Tyloses developed simultaneously within a single vessel but much separated in time among vessels. Pruning caused prodigious tylosis in vessels of grape stems, extending to approximately 1 cm deep and to 7 d after wounding, but about half of the vessels did not become completely occluded. The fraction of vessels forming tyloses was greatest in basal (85%) and least in apical (50%) regions. The depth of maximum density of tyloses was 4 mm from the cut in the basal region and 2 mm from the cut in the middle and apical regions. Tylose development was faster in the basal and middle than in the apical region. The pattern of tylose development is discussed in the context of wound repair and pathogen movement in grapevines. [ABSTRACT FROM AUTHOR]