Three New Pierces Disease Pathogenicity Effectors Identified Using Xylella fastidiosa Biocontrol Strain EB92-1Reportar como inadecuado

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Xylella fastidiosa X. fastidiosa infects a wide range of plant hosts and causes economically serious diseases, including Pierce-s Disease PD of grapevines. X. fastidiosa biocontrol strain EB92-1 was isolated from elderberry and is infectious and persistent in grapevines but causes only very slight symptoms under ideal conditions. The draft genome of EB92-1 revealed that it appeared to be missing genes encoding 10 potential PD pathogenicity effectors found in Temecula1. Subsequent PCR and sequencing analyses confirmed that EB92-1 was missing the following predicted effectors found in Temecula1: two type II secreted enzymes, including a lipase LipA; PD1703 and a serine protease PD0956; two identical genes encoding proteins similar to Zonula occludens toxins Zot; PD0915 and PD0928, and at least one relatively short, hemagglutinin-like protein PD0986. Leaves of tobacco and citrus inoculated with cell-free, crude protein extracts of E. coli BL21DE3 overexpressing PD1703 exhibited a hypersensitive response HR in less than 24 hours. When cloned into shuttle vector pBBR1MCS-5, PD1703 conferred strong secreted lipase activity to Xanthomonas citri, E. coli and X. fastidiosa EB92-1 in plate assays. EB92-1-PD1703 transformants also showed significantly increased disease symptoms on grapevines, characteristic of PD. Genes predicted to encode PD0928 Zot and a PD0986 hemagglutinin were also cloned into pBBR1MCS-5 and moved into EB92-1; both transformants also showed significantly increased symptoms on V. vinifera vines, characteristic of PD. Together, these results reveal that PD effectors include at least a lipase, two Zot-like toxins and a possibly redundant hemagglutinin, none of which are necessary for parasitic survival of X. fastidiosa populations in grapevines or elderberry.

Autor: Shujian Zhang, Pranjib K. Chakrabarty, Laura A. Fleites, Patricia A. Rayside, Donald L. Hopkins, Dean W. Gabriel



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