Although cereal crops all belong to the grass family (Poacea), most of their diseases are specific to a particular species. Thus, a given cereal species is typically resistant to diseases of other grasses, and this nonhost resistance is generally stable. To determine the feasibility of transferring nonhost resistance genes (R genes) between distantly related grasses to control specific diseases, we identified a maize R gene that recognizes a rice pathogen, Xanthomonas oryzae pv. oryzicola, which causes bacterial streak disease. Bacterial streak is an important disease of rice in Asia, and no simply inherited sources of resistance have been identified in rice. Although X. o. pv. oryzicola does not cause disease on maize, we identified a maize gene, Rxo1, that conditions a resistance reaction to a diverse collection of pathogen strains. Surprisingly, Rxo1 also controls resistance to the unrelated pathogen Burkholderia andropogonis, which causes bacterial stripe of sorghum and maize. The same gene thus controls resistance reactions to both pathogens and nonpathogens of maize. Rxo1 has a nucleotide-binding siteleucine-rich repeat structure, similar to many previously identified R genes. Most importantly, Rxo1 functions after transfer as a transgene to rice, demonstrating the feasibility of nonhost R gene transfer between cereals and providing a valuable tool for controlling bacterial streak disease.disease resistance ͉ nonhost resistance ͉ Xanthomonas
during the period of extensive cultivation as a result of evolution of the pathogen population.'Minghui 63' is a restorer line widely used in hybrid rice production A large number of genes for BB resistance have been in China. However, this line has become increasingly susceptible to identified that are available for cultivar improvement bacterial blight (BB), resulting in a rapid decline of its use in rice (Ogawa et al., 1989; Khush et al., 1990; Lin et al., 1996).production. The objective of this study was to improve the BB resis-However, it has been difficult to use these genes to tance of Minghui 63 by introgressing Xa21, a broad-spectrum BB resistance gene, into Minghui 63 by molecular marker-assisted selec-improve the resistance of the parents for the purpose tion (MAS). A polymerase chain reaction (PCR)-based MAS system of hybrid improvement. Incorporation of a resistance was established consisting of a marker that is a part of Xa21, a marker gene is difficult with conventional breeding methods located at 0.8 centimorgans (cM) from the Xa21 locus on one side, because of linkage with undesirable traits that is very and a marker at 3.0 cM from the gene on the other side. A total of 128 difficult to break even with many generations of backrestriction fragment length polymorphism (RFLP) markers, evenly crosses (Young and Tanksley, 1989). distributed on the 12 chromosomes, were used to recover the genetic Marker-assisted selection (MAS) has been advocated background of Minghui 63. The resulting improved version of Minghui
Objectives Natural remedies are becoming increasingly popular and important in the public and scientific communities. Historically, natural remedies have been shown to present interesting biological and pharmacological activity and are used as chemotherapeutic agents. For centuries Cordyceps, which is a genus of more than 400 species in the family Clavicipitaceae, has been used in traditional Chinese medicine. This study highlights the chemistry and pharmacology of Cordyceps, especially Cordyceps sinensis (Berk.) Sacc. and C. militaris (Fr.) L. Information was obtained from Google Scholar and the journal databases PubMed and Scopus. Key findings Many bioactive components of Cordyceps have been extracted, such as cordycepin, cordycepic acid, ergosterol, polysaccharides, nucleosides and peptides. Studies show that Cordyceps and its active principles possess a wide range of pharmacological actions, such as anti-inflammatory, antioxidant, antitumour, antihyperglycaemic, antiapoptosis, immunomodulatory, nephroprotective, and hepatoprotective. Summary More research is required to discover the full extent of the activity of Cordyceps.
The development of complex multispecies communities such as biofilms is controlled by interbacterial communication systems. We have previously reported an intergeneric communication between two oral bacteria, Streptococcus cristatus and Porphyromonas gingivalis, that results in inhibition of fimA expression. Here, we demonstrate that a surface protein, arginine deiminase (ArcA), of S. cristatus serves as a signal that initiates intergeneric communication. An ArcA-deficient mutant of S. cristatus is unable to communicate with P. gingivalis. Furthermore, arginase activity is not essential for the communication, and ArcA retains the ability to repress expression of fimA in the presence of arginine deiminase inhibitors. These results present a novel mechanism by which intergeneric communication in dental biofilms is accomplished.
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