MAX2 participates in an SCF complex which acts locally at the node to suppress shoot branching

The Arabidopsis gene ORE9/MAX2 encodes an F-box leucine-rich repeat protein. F-box proteins function as the substrate-recruiting subunit of SCF-type ubiquitin E3 ligases in protein ubiquitination. One of several phenotypes of max2 mutants, the highly branched shoot, is identical to mutants at three other MAX loci. Reciprocal grafting, double mutant analysis and gene cloning suggest that all MAX genes act in a common pathway, where branching suppression depends on MAX2 activity in the shoot, in response to an acropetally mobile signal that requires MAX3, MAX4 and MAX1 for its production. Here, we further investigate the site and mode of action of MAX2 in branching. Transcript analysis and a translational MAX2–GUS fusion indicate that MAX2 is expressed throughout the plant, most highly in developing vasculature, and is nuclear-localized in many cell types. Analysis of cell autonomy shows that MAX2 acts locally, either in the axillary bud, or in adjacent stem or petiole tissue. Expression of MAX2 from the CaMV 35S promoter complements the max2 mutant, does not affect branching in a wild-type background and partially rescues increased branching in the max1, max3 and max4 backgrounds. Expression of mutant MAX2, lacking the F-box domain, under the CaMV 35S promoter does not complement max2, and dominant-negatively affects branching in the wild-type background. Myc-epitope-tagged MAX2 interacts with the core SCF subunits ASK1 and AtCUL1 in planta. We conclude that axillary shoot growth is controlled locally, at the node, by an SCFMAX2, the action of which is enhanced by the mobile MAX signal

HIV in practice: current approaches and challenges in the diagnosis, treatment and management of HIV infection in Australia

As treatment improves, people living with HIV (PLWHIV) can now expect to live longer, which means that the foci of HIV-related care for them and their medical practitioners continue to change. With an increasingly older cohort of patients with HIV infection, practitioners’ key considerations are shifting from issues of acute treatment and patient survival to multiple comorbidities, toxicities associated with chronic therapy, and ongoing health maintenance. Within this context, this paper explores the current standard of practice for the management of HIV infection in Australia. We surveyed 56 Australian practitioners currently involved in managing HIV infection: ‘HIV section 100’ (HIV therapy-prescribing) general practitioners (s100 GPs; n = 26), sexual health physicians (SHPs; n = 24) and hospital-based physicians (HBPs; n = 6). Survey results for practice approaches and challenges were broadly consistent across the three practitioner specialties, apart from a few key areas. s100 GPs reported less prophylaxis use among patients whom they deemed at risk of HIV infection in comparison with SHPs, which may reflect differences in patient populations. Further, a higher proportion of s100 GPs nominated older HIV treatment regimens as their preferred therapy choices compared with the other specialties. In contrast with SHPs, s100 GPs were less likely to switch HIV therapies to simplify the treatment protocol, and to immediately initiate treatment upon patient request in those newly diagnosed with HIV infection. Considerably lower levels of satisfaction with current HIV practice guidelines were also reported by s100 GPs. It appears that greater support for s100 GPs may be needed to address these identified challenges and enhance approaches to HIV practice. Across all specialties, increasing access to mental health services for patients with HIV infection was reported as a key management issue. A renewed focus on providing improved mental health and wellbeing supports is recommended, particularly in the face of an ageing HIV-infected population

Can Genetically Engineered Crops Become Weeds?

There are significant differences if the distribution of weedy characteristics among weeds, normal plants, and crops. The world’s most serious weeds possess on the average 10 or 11 of these characters, a random collection of British plants have an average seven of the traits, and crop plants only five. For the average crop to become as “weedy” as the average weed, it would need to acquire five weedy traits. Even using the unlikely assumption that those traits are single loci in which a dominant mutation would provide the weedy character, this would require the simultaneous acquisition of five gene substitutions. Since the probability of multiple mutations is generally the joint probability of single mutations, the probability of changing the average crop to the average weed is (10-5), or 10-10. Even in the most numerous crop plants (perhaps 18 billion maize individuals are grown annually) this is not very probable. Since most of the crops listed are purchased from seed suppliers and not allowed to propagate, the plants will not gradually add weedy traits. Perennial and self-seeding crops, while more able to accumulate mutants, are generally grown in much smaller numbers. The probability of joint occurrence of new alleles producing significantly weedy plants from most crops is low. There are several important qualifications to this finding. First, the mean result is only a mean. There is much less difference between the extreme individuals of the different groups. For example, among the weeds, Cirsium arvense (Canada thistle) infests 27 crops in 37 countries but appears to have only six of 12 weedy characteristics while, among the crops, tomatoes (Lycopersicon esculentum) have seven of 13 weedy characteristics, making them “weedier” on this measure than the thistle. In addition, six of the 20 crop plants (30 percent) have weedy races, and nine of the 37 weeds (24.3 percent) are actively cultivated somewhere—indicating that the two categories actively exchange members. Even if a crop becomes a weed, only because cultivation is discontinued and not through evolution of weediness, a genetically engineered crop will still become a genetically engineered weed. The recent emergence of a seriously weedy race of millet (Panicum miliaceum) in Wisconsin and Minnesota after 200-300 years of cultivation in North America without weed problems emphasizes how much we do not understand about weed evolution. Until such events can be anticipated, there will be an ongoing risk of weeds derived from genetically engineered crops. This analysis should not be interpreted as a quick fix to problems of the new technology, but rather as directions for case-by-case problem solving. Plants with very low weediness and no weedy relatives are unlikely to be the source of weed populations in the future any more than they have been in the past (e.g., maize, pineapple). Plants with high inherent weediness and/or weedy relatives (oats, sunflowers) will, on the other hand, require serious scrutiny if we are to avoid additional problems. Moreover, study of the causes of weed success can suggest methods of modifying crop plants to reduce the risk of weed evolution. For example, infertile plants will have much less risk of producing weeds than fertile plants, due to lack of recombination, gene exchange, and propagules. Other approaches can also be suggested: poor seed longevity, careful management of vegetative reproduction, or dependence on cultivation practices, e.g. a trace mineral or soil disturbance for survival. To some degree, such dependencies already exist and could be exploited