RESUMEN
Improving crop species by breeding for salt tolerance or introducing salt tolerant traits is one method of increasing crop yields in saline affected areas. Extensive studies of the model plant species Arabidopsis thaliana has led to the availability of substantial information regarding the function and importance of many genes involved in salt tolerance. However, the identification and characterization of A. thaliana orthologs in species such as Brassica napus (oilseed rape) can prove difficult due to the significant genomic changes that have occurred since their divergence approximately 20 million years ago (MYA). The recently released Brassica rapa genome provides an excellent resource for comparative studies of A. thaliana and the cultivated Brassica species, and facilitates the identification of Brassica species orthologs which may be of agronomic importance. Sodium hydrogen antiporter (NHX) proteins transport a sodium or potassium ion in exchange for a hydrogen ion in the other direction across a membrane. In A. thaliana there are eight members of the NHX family, designated AtNHX1-8, that can be sub-divided into three clades, based on their subcellular localization: plasma membrane (PM), intracellular class I (IC-I) and intracellular class II (IC-II). In plants, many NHX proteins are primary determinants of salt tolerance and act by transporting Na(+) out of the cytosol where it would otherwise accumulate to toxic levels. Significant work has been done to determine the role of both PM and IC-I clade members in salt tolerance in a variety of plant species, but relatively little analysis has been described for the IC-II clade. Here we describe the identification of B. napus orthologs of AtNHX5 and AtNHX6, using the B. rapa genome sequence, macro- and micro-synteny analysis, comparative expression and promoter motif analysis, and highlight the value of these multiple approaches for identifying true orthologs in closely related species with multiple paralogs.
RESUMEN
The neuraminidase inhibitors (NAIs) are an effective class of antiviral drugs for the treatment of influenza A and B infections. Until recently, only a low prevalence of NAI resistance (<1%) had been detected in circulating viruses. However, surveillance in Europe in late 2007 revealed significant numbers of A(H1N1) influenza strains with a H274Y neuraminidase mutation that were highly resistant to the NAI oseltamivir. We examined 264 A(H1N1) viruses collected in 2008 from South Africa, Oceania and SE Asia for their susceptibility to NAIs oseltamivir, zanamivir and peramivir in a fluorescence-based neuraminidase inhibition assay. Viruses with reduced oseltamivir susceptibility were further analysed by pyrosequencing assay. The frequency of the oseltamivir-resistant H274Y mutant increased significantly after May 2008, resulting in an overall proportion of 64% (168/264) resistance among A(H1N1) strains, although this subtype represented only 11.6% of all isolates received during 2008. H274Y mutant viruses demonstrated on average a 1466-fold reduction in oseltamivir susceptibility and 527-fold reduction in peramivir sensitivity compared to wild-type A(H1N1) viruses. The mutation had no impact on zanamivir susceptibility. Ongoing surveillance is essential to monitor how these strains may spread or persist in the future and to evaluate the effectiveness of treatments against them.