Transcription activator-like effectors (TALEs) from Xanthomonas sp. have been used as customizable DNA-binding modules for genome-engineering applications. Ralstonia solanacearum TALE-like proteins (RTLs) exhibit similar structural features to TALEs, including a central DNA-binding domain composed of 35 amino acid-long repeats. Here, we characterize the RTLs and show that they localize in the plant cell nucleus, mediate DNA binding, and might function as transcriptional activators. RTLs have a unique DNA-binding architecture and are enriched in repeat variable di-residues (RVDs), which determine repeat DNA-binding specificities. We determined the DNA-binding specificities for the RVD sequences ND, HN, NP, and NT. The RVD ND mediates highly specific interactions with C nucleotide, HN interacts specifically with A and G nucleotides, and NP binds to C, A, and G nucleotides. Moreover, we developed a highly efficient repeat assembly approach for engineering RTL effectors. Taken together, our data demonstrate that RTLs are unique DNA-targeting modules that are excellent alternatives to be tailored to bind to user-selected DNA sequences for targeted genomic and epigenomic modifications. These findings will facilitate research concerning RTL molecular biology and RTL roles in the pathogenicity of Ralstonia spp.

Sugarcane is an important international commodity as a valuable agricultural crop especially in developing countries. Sequencing was carried out to generate >35,000 expressed sequence tags (ESTs) from healthy as well as red-rot-infected tissue of Indian subtropical variety of sugarcane. Subsequent clustering with existing sugarcane ESTs in public databases identified 4,087 clusters, including 85 clusters that preferentially express upon Colletotrichum falcatum (red-rot) infection, which were previously unreported. Real-time reverse transcription-PCR profiling of selected EST clusters identified several sugarcane clusters that show differential expression in response to biotic and abiotic stress conditions. Twenty-five stress-related clusters showed >2-fold relative expression during water-deficit stress in sugarcane. Similarly, EST clusters could be identified, which exhibit association with red-rot disease when assessed in red-rot-susceptible and red-rot-resistant varieties of sugarcane. Such EST clusters are good candidates for in-depth analysis to elucidate stress-responsive pathways in sugarcane and facilitate genetic manipulation to tailor this crop for tolerance to various stresses.

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Red rot is a serious disease of sugarcane caused by the fungus Colletotrichum falcatum that has a colossal damage potential. The fungus, prevalent mainly in the Indian sub-continent, keeps on producing new pathogenic strains leading to breakdown of resistance in newly released varieties and hence the deployment of linked markers for marker-assisted selection for resistance to this disease can fine tune the breeding programme. This study based on a panel of 119 sugarcane genotypes fingerprinted for 944 SSR alleles was undertaken with an aim to identify marker-trait associations (MTAs) for resistance to red rot. Mixed linear model containing population structure and kinship as co-factor detected four MTAs that were able to explain 10-16 % of the trait variation, individually. Among the four MTAs, EST sequences diagnostic of three could be BLAST searched to the sorghum genome with significant sequence homology. Several genes encoding important plant defence related proteins, viz., cytochrome P450, Glycerol-3-phosphate transporter-1, MAP Kinase-4, Serine/threonine-protein kinase, Ring finger domain protein and others were localized to the vicinity of these MTAs. These positional candidate genes are worth of further investigation and possibly these could contribute directly to red rot resistance, and may find a potential application in marker-assisted sugarcane breeding.