This work reports the evaluation of citrus canker resistance in transgenic lines of four sweet orange cultivars Hamlin, Natal, Pera and Valencia expressing the rice Xa21 R-gene. The Agrobacterium-mediated genetic transformation was performed and transgene integration was confirmed by Southern blot analyses. These analyses showed that the plants had undergone 1-3 independent transgene integration events. The genetic transformation efficiency was 18AE6% for Hamlin, 8AE3% for Natal, 3% for Pera and 11AE3% for Valencia sweet orange. Transgene transcription was confirmed by northern blot analyses in most transgenic lines analysed. Transgenic lines of each of the cultivars were selected and propagated for resistance evaluation to Xanthomonas axonopodis pv. citri. Transgenic lines with a higher resistance to citrus canker were identified for cvs Hamlin, Natal and Pera. The lowest diseased leaf area values were detected for transgenic lines of Natal and Pera, cultivars which are considered moderately resistant to citrus canker in the field, indicating an influence of cultivar genetic background on the effectiveness of the Xa21 gene in controlling the pathogen. Transgenic lines in which transgene transcription was not detected did not show any improvement in resistance to the pathogen. These results show the integration and expression of the rice Xa21 gene in citrus and the possibility of using R-genes in controlling diseases in a heterologous genetic background.

The cyanobacterial genus Nostoc is an important contributor to carbon and nitrogen bioavailability in terrestrial ecosystems and a frequent partner in symbiotic relationships with non-diazotrophic organisms. However, since this currently is a polyphyletic genus, the diversity of Nostoc -like cyanobacteria is considerably underestimated at this moment. While reviewing the phylogenetic placement of previously isolated Nostoc -like cyanobacteria originating from Brazilian Amazon, Caatinga and Atlantic forest samples, we detected 17 strains isolated from soil, freshwater, rock and tree surfaces presenting patterns that diverged significantly from related strains when ecological, morphological, molecular and genomic traits were also considered. These observations led to the identification of the evaluated strains as representative of three novel nostocacean genera and species: Amazonocrinis nigriterrae gen. nov., sp. nov.; Atlanticothrix silvestris gen. nov., sp. nov.; and Dendronalium phyllosphericum gen. nov., sp. nov., which are herein described according to the rules of the International Code of Nomenclature for algae, fungi and plants. This finding highlights the great importance of tropical and equatorial South American ecosystems for harbouring an unknown microbial diversity in the face of the anthropogenic threats with which they increasingly struggle.

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The saline-alkaline lakes (soda lakes) are the habitat of the haloalkaliphilic cyanobacterium Anabaenopsis elenkinii, the type species of this genus. To obtain robust phylogeny of this type species, we have generated whole-genome sequencing of the bloom-forming Anabaenopsis elenkinii strain CCIBt3563 isolated from a Brazilian soda lake. This strain presents the typical morphology of A. elenkinii with short and curved trichomes with apical heterocytes established after separation of paired intercalary heterocytes and also regarding to cell dimensions. Its genome size is 4 495 068 bp, with a G+C content of 41.98 %, a total of 3932 potential protein coding genes and four 16S rRNA genes. Phylogenomic tree inferred by RAxML based on the alignment of 120 conserved proteins using GTDB-Tk grouped A. elenkinii CCIBt3563 together with other genera of the family Aphanizomenonaceae. However, the only previous available genome of Anabaenopsis circularis NIES-21 was distantly positioned within a clade of Desikacharya strains, a genus from the family Nostocaceae. Furthermore, average nucleotide identity values from 86–98 % were obtained among NIES-21 and Desikacharya genomes, while this value was 76.04 % between NIES-21 and the CCIBt3563 genome. These findings were also corroborated by the phylogenetic tree of 16S rRNA gene sequences, which also showed a strongly supported subcluster of A. elenkinii strains from Brazilian, Mexican and Kenyan soda lakes. This study presents the phylogenomics and genome-scale analyses of an Anabaenopsis elenkinii strain, improving molecular basis for demarcation of this species and framework for the classification of cyanobacteria based on the polyphasic approach.

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