Transcription Activator-Like Effectors Diversity in Iranian Strains of Xanthomonas translucens

Abstract

Bacterial leaf streak caused by different pathovars of Xanthomonas translucens is the most important seedborne bacterial disease of small grain cereals. However, variations in the virulence-associated genomic areas of the pathogen remain uninvestigated. In this study, the diversity of transcription activator-like effectors (TALE) was investigated using the Southern blotting of BamHI-digested genomic DNAs in the Iranian strains of X. translucens. All 65 X. translucens strains were assigned into 13 genotypes, where 57 X. translucens pv. undulosa strains were placed in genotypes 1 to 8, and seven X. translucens pv. translucens strains were placed in genotypes 9 to 12. Interestingly, we did not find any TALE genes in the strain XtKm7 (genotype 13), which showed to be pathogenic only on barley. Virulence and aggressiveness of these strains in greenhouse conditions were in agreement with the TALE-based clustering of the strains in the pathovar level, though variations were observed in the aggressiveness of X. translucens pv. undulosa strains. In general, strains containing higher numbers of putative TALE genes were more virulent on wheat and barley than strains containing fewer. This is the first TALE-based genetic diversity analysis on X. translucens strains and provides novel insights into the virulence repertories and genomic characteristics of the pathogen. Further investigations using TALE mutagenesis and complementation analysis are warranted to precisely elucidate the role of each detected X. translucens TALE in bacterial virulence and aggressiveness either on wheat or barley.

Genomics-Enabled Novel Insight Into the Pathovar-Specific Population Structure of the Bacterial Leaf Streak Pathogen Xanthomonas translucens in Small Grain Cereals

“…translucens strains: XtKm8, XtKm9, and XtKm34 were selected from a collection of 57 strains isolated from wheat and barley in Iran during 2008 to 2017 (Khojasteh et al, 2019). The criteria used for selection of the strains were their host range and pathovar status, MLSA-based genetic diversity and TALE repertories of the strains (Khojasteh et al, 2020). The bacterial strains were streaked onto nutrient agar (NA) medium or nutrient broth medium (NB: NA without agar) when required and incubated at 28 • C. All the strains were stored at −80 • C in nutrient broth (NB) medium amended with 50% sterile glycerol.…”

“…The T3Es are further categorized into TALEs (transcription activator-like effectors) and non-TALEs which also known as Xops (Xanthomonas outer proteins). It has been shown that the bacterial leaf streak pathogen isolated from barley and wheat crops possess high genetic diversity in terms of TALEs (Khojasteh et al, 2020). During the past decade, high throughput complete genome sequencing technologies have provided substantial progresses in the understanding of molecular mechanisms underlying plant colonization, pathogenicity and survival of the bacterial leaf streak pathogens (Sapkota et al, 2020).…”

“…Recently, a TALE named Xtu 4699_Tal8 has functionally been characterized, inducing expression of wheat gene TaNCED located on short arm of chromosome 5B to promote disease susceptibility (Peng et al, 2019). Despite the abundance of data on geographic distribution and genetic diversity of the bacterial leaf streak agents (Curland et al, 2018;Khojasteh et al, 2020), complete genome sequence-based population structure and genomic repertories of the pathogens mostly remain uninvestigated.…”

“…translucens strains among a collection of 57 strains isolated in Iran during the past couple of decades (Khojasteh et al, 2019). The representative strains were selected based on their host range and pathovar status, multilocus sequence analysis and typing (MLSA/MLST) scheme as well as the Southern blot-based TALE diversity as described previously (Khojasteh et al, 2020). The strains were sequenced using Oxford Nanopore PromethION long-read direct DNA sequencing platform.…”

Identification of a virulence tal gene in the cotton pathogen, Xanthomonas citri pv. malvacearum strain Xss-V2–18

“…The number and diversity of tal effector genes varies among different species, pathovars and strains of Xanthomonas. For example, Xoo strains harbor [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] TALEs [49][50][51][52][53], Xoc strains contain 19-28 [49,54,55], Xtt strains contains 5-12 [56], Xtu strains contains 7-8 [56][57][58] and Xcm strains harbor 8-12 genes encoding tal effectors [27,46,59]. Some Xanthomonas spp.…”