Insights into the Activity and Substrate Binding of Xylella fastidiosa Polygalacturonase by Modification of a Unique QMK Amino Acid Motif Using Protein Chimeras

Screening of Sugarcane Proteins Associated with Defense against Leifsonia xyli subsp. xyli, Agent of Ratoon Stunting Disease

Sugarcane is the most important sugar crop and one of the leading energy-producing crops in the world. Ratoon stunting disease (RSD), caused by the bacterium Leifsonia xyli subsp. xyli, poses a huge threat to ratoon crops, causing a significant yield loss in sugarcane. Breeding resistant varieties is considered the most effective and fundamental approach to control RSD in sugarcane. The exploration of resistance genes forms the foundation for breeding resistant varieties through molecular technology. The pglA gene is a pathogenicity gene in L. xyli subsp. xyli, encoding an endopolygalacturonase. In this study, the pglA gene from L. xyli subsp. xyli and related microorganisms was analyzed. Then, a non-toxic, non-autoactivating pglA bait was successfully expressed in yeast cells. Simultaneously the yeast two-hybrid library was generated using RNA from the L. xyli subsp. xyli-infected sugarcane. Screening the library with the pglA bait uncovered proteins that interacted with pglA, primarily associated with ABA pathways and the plant immune system, suggesting that sugarcane employs these pathways to respond to L. xyli subsp. xyli, triggering pathogenicity or resistance. The expression of genes encoding these proteins was also investigated in L. xyli subsp. xyli-infected sugarcane, suggesting multiple layers of regulatory mechanisms in the interaction between sugarcane and L. xyli subsp. xyli. This work promotes the understanding of plant-pathogen interaction and provides target proteins/genes for molecular breeding to improve sugarcane resistance to L. xyli subsp. xyli.

Genome sequence analysis of an extensively drug-resistant Acinetobacter baumannii indigo-pigmented strain depicts evidence of increase genome plasticity

Acinetobacter baumannii is a multidrug resistant nosocomial pathogen that shows an outstanding ability to undergo genetic exchange, thereby acquiring different traits that contribute to its success. In this work, we identified genetic features of an indigo-pigmented A. baumannii strain (Ab33405) that belongs to the clonal complex CC113B/CC79P. Ab33405 possesses a high number of genes coding for antibiotic resistance and virulence factors that may contribute to its survival, not only in the human host, but also in the hospital environment. Thirteen genes conferring resistance to different antibiotic families (trimethoprim, florfenicol, β-lactams, aminoglycosides and sulfonamide) as well as the adeIJK genes and the capsule locus (KL) and outer core locus (OCL) were identified. Ab33405 includes 250 unique genes and a significant number of elements associated with Horizontal Gene Transfer, such as insertion sequences and transposons, genomic islands and prophage sequences. Also, the indigo-pigmented uncommon phenotype that could be associated with the monooxygenase or dioxygenase enzyme coded for by the iacA gene within the iac cluster was probably conferred by insertion of a 18-kb DNA fragment into the iacG gene belonging to this cluster. The Ab33405 genome includes all type VI secretion system genes and killing assays showed the ability of Ab33045 to kill Escherichia coli. In addition, Ab33405 can modulate susceptibility antibiotics when exposed to blue light.

Functional and Evolutionary Characterization of a UDP-Xylose Synthase Gene from the Plant Pathogen Xylella fastidiosa, Involved in the Synthesis of Bacterial Lipopolysaccharide

Xylella fastidiosa is a plant-infecting bacillus, responsible for many important crop diseases, such as Pierce's disease of vineyards, citrus variegated chlorosis, and coffee leaf scorch (CLS), among others. Recent genomic comparisons involving two CLS-related strains, belonging to X. fastidiosa subsp. pauca, revealed that one of them carries a frameshift mutation that inactivates a gene encoding an oxidoreductase of the short-chain dehydrogenase/reductase (SDR) superfamily, which may play important roles in determining structural variations in bacterial glycans and glycoconjugates. However, the exact nature of this SDR has been a matter of controversy, as different annotations of X. fastidiosa genomes have implicated it in distinct reactions. To confirm the nature of this mutated SDR, a comparative analysis was initially performed, suggesting that it belongs to a subgroup of SDR decarboxylases, representing a UDP-xylose synthase (Uxs). Functional assays, using a recombinant derivative of this enzyme, confirmed its nature as XfUxs, and carbohydrate composition analyses, performed with lipopolysaccharide (LPS) molecules obtained from different strains, indicate that inactivation of the X. fastidiosa uxs gene affects the LPS structure among CLS-related X. fastidiosa strains. Finally, a comparative sequence analysis suggests that this mutation is likely to result in a morphological and evolutionary hallmark that differentiates two subgroups of CLS-related strains, which may influence interactions between these bacteria and their plant and/or insect hosts.