Comparison of gene activation by two TAL effectors from Xanthomonas axonopodis pv. manihotis reveals candidate host susceptibility genes in cassava

Abstract

Xanthomonas axonopodis pv. manihotis (Xam) employs transcription activator-like (TAL) effectors to promote bacterial growth and symptom formation during infection of cassava. TAL effectors are secreted via the bacterial type III secretion system into plant cells, where they are directed to the nucleus, bind DNA in plant promoters and activate the expression of downstream genes. The DNA-binding activity of TAL effectors is carried out by a central domain which contains a series of repeat variable diresidues (RVDs) that dictate the sequence of bound nucleotides. TAL14Xam668 promotes virulence in Xam strain Xam668 and has been shown to activate multiple cassava genes. In this study, we used RNA sequencing to identify the full target repertoire of TAL14Xam668 in cassava, which includes over 50 genes. A subset of highly up-regulated genes was tested for activation by TAL14CIO151 from Xam strain CIO151. Although TAL14CIO151 and TAL14Xam668 differ by only a single RVD, they display differential activation of gene targets. TAL14CIO151 complements the TAL14Xam668 mutant defect, implying that shared target genes are important for TAL14Xam668 -mediated disease susceptibility. Complementation with closely related TAL effectors is a novel approach to the narrowing down of biologically relevant susceptibility genes of TAL effectors with multiple targets. This study provides an example of how TAL effector target activation by two strains within a single species of Xanthomonas can be dramatically affected by a small change in RVD-nucleotide affinity at a single site, and reflects the parameters of RVD-nucleotide interaction determined using designer TAL effectors in transient systems.

TALE-induced bHLH transcription factors that activate a pectate lyase contribute to water soaking in bacterial spot of tomato

“…Identifying and characterizing S genes reveals pathogen strategies and is useful in the design of disease resistant plants, for example through the removal of relevant EBEs via DNA editing technologies (9). For TALEs that activate multiple host gene targets, such as those with EBEs that partially span a TATA box, it becomes increasingly challenging to identify the bona fide S gene(s) (14,15). To probe single genes for pathogenicity functions, designer TALEs (dTALEs) can be constructed and tested in planta for virulence contributions (16).…”

Distribution of Cassava Bacterial Blight and Reaction of Selected Cassava Genotypes to the Disease in Kenya

“…The isolates were able to amplify and hence were detected with the primer combination RB1/RB2 whose target gene was the transcription activator like effectors (TAL effectors). TAL effectors are known to promote bacterial growth which in turn results in symptom formation during infection (Cohn et al 2016). Upon coming into contact with the plant the bacteria delivers the TAL effectors into the plant suppressing host immunity and promoting pathogenesis (Cohn et al 2016).…”

“…The method described by Cohn et al (2016) was used in culturing and PCR amplification of the bacteria. The isolates were grown in nutrient agar for 48 hours before extraction.…”

daTALbase: A Database for Genomic and Transcriptomic Data Related to TAL Effectors

“…The working version of the cassava database integrates publicly available data corresponding to seven TALEs sequences from Xanthomonas axnopodis pv. manihotis (Bart et al 2012;Castiblanco et al 2013), their predicted targets on the cassava genome (v 6.1) (Bredeson et al 2016), and two sets of RNA-seq data (Cohn et al 2016(Cohn et al , 2014Muñ oz-Bodnar et al 2014). We expect to expand this database to include newly sequenced TALEs upon their release.…”