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Cell wall polysaccharide architecture and its potential impacts on grapevine susceptibility to Pierce’s disease

Qiang Sun: University of Wisconsin-Stevens Point

<div><span style="font-family:'Arial';">Pierce’s disease (PD) symptom development of grapevine is largely dependent on the systemic spread of the bacterial pathogen <em><span style="font-family:'Arial';">Xylella fastidiosa</span></em> (<em><span style="font-family:'Arial';">Xf</span></em>) in a vine’s vessel system. A major barrier to this spread is the intervessel pit membrane (PM), a cell wall structure that separates adjacent vessels. It is believed that <em><span style="font-family:'Arial';">Xf</span></em> is able to degrade these PMs by attacking various polysaccharides with its cell wall degrading enzymes (CWDEs), enlarging the PMs’ porosity and enabling its systemic spread. Therefore, it is important to know the polysaccharide composition and architecture of the PMs. However, the details on these remain unclear. This study focuses on four potential polysaccharide targets of the <em><span style="font-family:'Arial';">Xf</span></em>’s CWDEs: fucosylated xyloglucans (F-XyGs), xylans, heavily and weakly methyl-esterified homogalacturonans (HMe-HGs and WMe-HGs). Using immunogold- scanning electron microscopy, we found that these polysaccharides differed in both quantity and spatial distribution in PMs of PD-susceptible Chardonnay vines. Xylans and HMe-HGs were undetectable in the superficial layer of a PM, but gradually increased in quantity toward deeper layers with more xylans than HMe-HGs. F-XyGs occurred in small amount in the superficial layer but were abundant in all the underlayers, while WMe-HGs were abundant in the superficial layer and decreased in quantity toward deeper layers. This information should be valuable for the understanding of <em><span style="font-family:'Arial';">Xf</span></em>-host vine interactions and the mechanism of grapevine’s PD susceptibility.</span></div>