The Enigma of <Emphasis Type="Italic">Solanum maglia</Emphasis> in the Origin of the Chilean Cultivated Potato, <Emphasis Type="Italic">Solanum tuberosum</Emphasis> Chilotanum Group<Superscript>1</Superscript>

The Enigma of Solanum maglia in the Origin of the Chilean Cultivated Potato, Solanum tuberosum Chilotanum Group. Landrace potato cultivars occur in two broad geographic regions: the high Andes from western Venezuela south to northern Argentina (Solanum tuberosum Andigenum Group, “Andigenum”), and lowland south-central Chile (S. tuberosum Chilotanum Group, “Chilotanum”), with a coastal desert and 560 km between southernmost populations of Andigenum and Chilotanum. Unlike Andigenum landraces, Chilotanum landraces are adapted to long days and carry a 241 base pair plastid DNA deletion. However, Andigenum and Chilotanum landraces are morphologically similar. We investigated a hypothesis that Chilotanum landraces arose from Solanum maglia, a rare tuber-bearing species found in Chile and Argentina. This hypothesis was formulated first based on morphological analyses of starch grains of extant and preserved (12,500 years before present) S. maglia, and on putative sympatry of extant S. maglia and Chilotanum landraces. Our new starch grain analyses fail to support this hypothesis; we could find no evidence of current sympatric distributions, and S. maglia lacks the 241-bp plastid deletion. However, microsatellite data group all accessions of S. maglia exclusively with Chilotanum, which is supported by our previous observation at the single locus of the waxy gene. These results could be interpreted in various ways, but all explanations have problems. One explanation is that S. maglia is a progenitor of Chilotanum. However, the plastid deletion in Chilotanum but not S. maglia cannot be easily explained. Another explanation is that Chilotanum was formed by hybridization between S. maglia and pre-Chilotanum, but this conflicts with prior cladistic analyses. These new data shed light on aspects of this question and highlight various evolutionary scenarios, but the origin of Chilotanum and the involvement of S. maglia in its origin remain an enigma.     

The protein phosphatase PP2A/Bα binds to the microtubule-associated proteins Tau and MAP2 at a motif also recognized by the kinase Fyn: implications for tauopathies

The predominant brain microtubule-associated proteins MAP2 and tau play a critical role in microtubule cytoskeletal organization and function. We have previously reported that PP2A/Bα, a major protein phosphatase 2A (PP2A) holoenzyme, binds to and dephosphorylates tau, and regulates microtubule stability. Here, we provide evidence that MAP2 co-purifies with and is dephosphorylated by endogenous PP2A/Bα in bovine gray matter. It co-localizes with PP2A/Bα in immature and mature human neuronal cell bodies. PP2A co-immunoprecipitates with and directly interacts with MAP2. Using in vitro binding assays, we show that PP2A/Bα binds to MAP2c isoforms through a region encompassing the microtubule-binding domain and upstream proline-rich region. Tau and MAP2 compete for binding to and dephosphorylation by PP2A/Bα. Remarkably, the protein-tyrosine kinase Fyn, which binds to the proline-rich RTPPKSP motif conserved in both MAP2 and tau, inhibits the interaction of PP2A/Bα with either tau or MAP2c. The corresponding synthetic RTPPKSP peptide, but not the phosphorylated RpTPPKSP version, competes with Tau and MAP2c for binding to PP2A/Bα. Significantly, down-regulation of PP2A/Bα and deregulation of Fyn-Tau protein interactions have been linked to enhanced tau phosphorylation in Alzheimer disease. Together, our results suggest that PP2A/Bα is part of segregated MAP2 and tau signaling scaffolds that can coordinate the action of key kinases and phosphatases involved in modulating neuronal plasticity. Deregulation of these compartmentalized multifunctional protein complexes is likely to contribute to tau deregulation, microtubule disruption, and altered signaling in tauopathies.     

Portage connectivity does not predict establishment success of canoe-mediated dispersal for crustacean zooplankton

Although community structure may be largely determined by local abiotic and biotic conditions under moderate levels of dispersal, anthropogenic activities can enhance dispersal rates far beyond what would otherwise occur in natural systems. We investigated the potential impact of recreational canoeing on crustacean zooplankton community structure in Killarney Provincial Park, Canada, where canoes that are transported between lakes via portage routes may enhance zooplankton community connectivity by providing a dispersal “short-cut.” We conducted a study to (1) quantify zooplankton attachment to canoe hulls after paddling through a lake and assess the importance of canoes to overall seasonal dispersal within a lake relative to other means of dispersal, (2) test the prediction that zooplankton survivorship is negatively correlated with portage duration using a mesocosm experiment, and (3) test whether variation in lake community composition was better explained by models based on reduced portage-corrected distances or true edge-to-edge distances between lakes along popular canoe routes. Here, we report the findings that canoes have the potential to act as frequent dispersal vectors, but appear to have little impact on community structure in portage-connected lakes. Substantial numbers of adult zooplankton became attached to canoe hulls and were able to establish viable populations even after exposure to portage conditions for 30 min. However, canoe-mediated dispersal only accounted for a very small proportion (<1% in this case) of overall seasonal dispersal. Moreover, environmental variables explained the greatest amount of variation in community composition among park lakes. Nevertheless, this study indicates that canoe dispersal could be more effective for specific species such as Sida crystallina than is evident by analysis of entire communities and could facilitate the spread of invasive species amenable to attaching to boat hulls. Thus, the debate about whether community composition is more strongly influenced by local environmental conditions or regional dispersal may vary depending on the scale of consideration (i.e., individual species vs. whole community).