Agrobacterium‐mediated transfer from a binary vector was used to produce transgenic Nicotiana tabacum plants that expressed coat protein of the plant virus, alfalfa mosaic virus (AMV). Expression levels of the chimeric gene, which was under the control of the cauliflower mosaic virus 19S promoter, were determined in primary transformed plants, in the progeny from self‐fertilization and in the progeny from crosses to normal tobacco. RNA transcripts that were of the expected size as well as a protein of the Mr and antigenicity of AMV coat protein accumulated in the transgenic plants. Plants that expressed the highest levels of coat protein developed fewer primary infections following inoculation with two strains of AMV and developed systemic infection slower than did plants that did not express coat protein. Resistance was specifically against virions of the AMV strains. AMV RNA and the unrelated virus, tobacco mosaic virus, were as infectious on progeny that expressed coat protein as they were on progeny that did not. The relationship between the virus resistance expressed by these transgenic plants and that observed in virus cross‐protection is discussed.
SUMMARYCross-protection reactions of two tobamoviruses, sunn-hemp mosaic virus (SHMV) and common tobacco mosaic virus (TMV-C), were investigated and compared. A mutant of SHMV (SHMV-n), produced by nitrous acid treatment, induced necrotic lesions in bean. SHMV protected completely against this mutant and against SHMV-n RNA. SHMV in bean protected only weakly, however, against TMV-C. To determine whether the coat protein of these viruses affected the ability to superinfect, RNA of each virus was encapsidated in the coat protein of the other. TMV-C RNA encapsidated in SHMV coat protein was five-to 27-fold less infectious on SHMVinfected bean leaves than TMV-C RNA re-encapsidated in TMV-C coat protein.When homologous or heterologous coat protein was added to inocula, infectivity for healthy plants was diminished markedly more by homologous protein, suggesting that extraneous homologous protein diminished infectivity by inhibiting viral uncoating. SHMV-n RNA encapsidated in TMV-C coat protein did not superinfect SHMVinfected bean leaves. Thus, although coat protein was shown to be a factor in crossprotection in some situations, other factors must also be involved.
In the area of hands-on science with the public, microbiology poses particular challenges in offering activities that are safe and cheap, as well as intriguing and engaging. We developed MicroSafari as part of our work with the UW–Madison Biology Outreach Club (BOC), an all-volunteer organization of biology graduate students. During the period 2005–2009, we led over a dozen MicroSafaris at venues on campus and in communities, for groups of families and youth, with group size ranging from 30 to 100. The MicroSafari is a hands-on version of Dyer’s Field Guide, using theater-based elements to share examples of these macroscopic characteristics of microscopic organisms.
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