Open AccessAn engineered promoter driving expression of a microbial avirulence gene confers recognition of TAL effectors and reduces growth of diverse Xanthomonas strains in citrus
Author(s) -
Shantharaj Deepak,
Römer Patrick,
Figueiredo Jose F. L.,
Minsavage Gerald V.,
Krönauer Christina,
Stall Robert E.,
Moore Gloria A.,
Fisher Latanya C.,
Hu Yang,
Horvath Diana M.,
Lahaye Thomas,
Jones Jeffrey B.
Publication year - 2017
Publication title -
molecular plant pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.945
H-Index - 103
eISSN - 1364-3703
pISSN - 1464-6722
DOI - 10.1111/mpp.12454
Subject(s) - biology , effector , xanthomonas , gene , microbiology and biotechnology , gene expression , genetics , xanthomonas citri , botany
Summary Xanthomonas citri ssp. citri ( X. citri ), causal agent of citrus canker, uses transcription activator‐like effectors (TALEs) as major pathogenicity factors. TALEs, which are delivered into plant cells through the type III secretion system (T3SS), interact with effector binding elements ( EBE s) in host genomes to activate the expression of downstream susceptibility genes to promote disease. Predictably, TALEs bind EBE s in host promoters via known combinations of TALE amino acids to DNA bases, known as the TALE code. We introduced 14 EBE s, matching distinct X. citri TALEs, into the promoter of the pepper Bs3 gene ( ProBs3 1EBE ), and fused this engineered promoter with multiple EBE s ( ProBs3 14EBE ) to either the β‐glucuronidase ( GUS ) reporter gene or the coding sequence (cds) of the pepper gene, Bs3 . TALE‐induced expression of the Bs3 cds in citrus leaves resulted in no visible hypersensitive response (HR). Therefore, we utilized a different approach in which ProBs3 1EBE and ProBs3 14EBE were fused to the Xanthomonas gene, avrGf1 , which encodes a bacterial effector that elicits an HR in grapefruit and sweet orange. We demonstrated, in transient assays, that activation of ProBs3 14EBE by X. citri TALEs is T3SS dependent, and that the expression of AvrGf1 triggers HR and correlates with reduced bacterial growth. We further demonstrated that all tested virulent X. citri strains from diverse geographical locations activate ProBs3 14EBE . TALEs are essential for the virulence of X. citri strains and, because the engineered promoter traps are activated by multiple TALEs, this concept has the potential to confer broad‐spectrum, durable resistance to citrus canker in stably transformed plants.