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Karyotypes of 27 species in Leucadendron are analysed for the first time. New chromosome counts are reported for 15 species, with 2 n = 26 occurring in all of them. Karyotype analysis indicated that chromosomes of Leucadendron taxa are small in size and have predominantly median to submedian centromeres. The mean sizes of somatic metaphase chromosomes ranged from 1.05 to 2.65 µm. Based on Stebbins’ karyotype classification, 1A type was found in L. galpinii, L. muirii, L. orientale, L. platyspermum, L. rubrum, and L. salignum; 2A type in L. conicum, L. flexuosum, L. laureolum, L. meridianum, L. salicifolium, L. stelligerum, and L. teretifolium; and 2B type in L. argenteum, L. chamelaea, L. discolor, L. elimense, L. eucalyptifolium, L. floridum, L. gandogeri, L. linifolium, L. loeriense, L. macowanii, L. procerum, L. spissifolium, L. strobilinum, and L. tinctum. These types are the three most symmetrical karyotypes and are considered to be primitive. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 151, 387–394. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Emergence of plasmid-mediated colistin resistance mechanism MCR-1 in animals and human beings in China: a microbiological and molecular biological study," by Y. Y. Liu and colleagues in the 2016 issue.

The proper use of resistance genes (R genes) requires a comprehensive understanding of their genomics and evolution. We analyzed genes encoding nucleotide-binding sites and leucine-rich repeats in the genomes of rice (Oryza sativa), maize (Zea mays), sorghum (Sorghum bicolor), and Brachypodium distachyon. Frequent deletions and translocations of R genes generated prevalent presence/absence polymorphism between different accessions/species. The deletions were caused by unequal crossover, homologous repair, nonhomologous repair, or other unknown mechanisms. R gene loci identified from different genomes were mapped onto the chromosomes of rice cv Nipponbare using comparative genomics, resulting in an integrated map of 495 R loci. Sequence analysis of R genes from the partially sequenced genomes of an African rice cultivar and 10 wild accessions suggested that there are many additional R gene lineages in the AA genome of Oryza. The R genes with chimeric structures (termed type I R genes) are diverse in different rice accessions but only account for 5.8% of all R genes in the Nipponbare genome. In contrast, the vast majority of R genes in the rice genome are type II R genes, which are highly conserved in different accessions. Surprisingly, pseudogene-causing mutations in some type II lineages are often conserved, indicating that their conservations were not due to their functions. Functional R genes cloned from rice so far have more type II R genes than type I R genes, but type I R genes are predicted to contribute considerable diversity in wild species. Type I R genes tend to reduce the microsynteny of their flanking regions significantly more than type II R genes, and their flanking regions have slightly but significantly lower G/C content than those of type II R genes. [ABSTRACT FROM AUTHOR]