GROWTH DYNAMICS OF BLACK SPRUCE (PICEA MARIANA) ACROSS NORTHWESTERN NORTH AMERICA

The impacts of climate change have been widely documented around the world. One of the most rapidly changing areas is the boreal forest of North America. The extent of change has been such that there have been shifts in long-standing climate-growth relationships in many boreal tree species; while the growth of many of these high-latitude forests were formerly limited by temperature, warming has increased the evapotranspirative demands such that there is widespread drought stress limiting productivity in the boreal forest. With the importance of the boreal forest as a global carbon sink, it is imperative to understand the extent of these changes, and to predict the resilience of the boreal forest in the face of continued climate change. One area of the boreal forest that has not been extensively studied, despite some of the most extreme warming, is northwestern Canada. Black spruce, the most widespread and dominant of North American boreal trees, is particularly under-studied in this region. In my doctoral research, I have sought to fill some of these knowledge gaps regarding black spruce growth dynamics across its latitudinal extent in northwestern Canada through addressing three main objectives: (1) Investigate the effects of permafrost thaw on the growth dynamics of black spruce in a discontinuous permafrost peatland; (2) Compare the productivity and main climatic drivers of black spruce growth across the latitudinal extent of the species in northwestern Canada; (3) Quantify the degree of plasticity vs. local adaptation in determining black spruce growth responses to resource availability in a common garden study. The results of this research highlight the variability in black spruce growth dynamics across this broad climate and permafrost gradient. While productivity has increased at the northern and southern margins of the boreal forest, the mid-latitude site in the discontinuous permafrost peatland has demonstrated dramatic declines in productivity. I demonstrate that this can be attributed to the negative impacts of permafrost thaw-induced drought stress, wherein the thickening of the active layer is reducing the capacity of shallow-rooted black spruce to access the water table. Thus, decreased growth at this site is an indirect effect of warming. At the northern margins of black spruce, growth is increasing as a result of warming, likely as it can drive longer growing seasons and increased nutrient mineralization. Growth at the southern margin does not appear to be driven by either temperature or precipitation alone, however growth patterns appear to be influenced by water balance at the site as well as CO2 fertilization. The common garden study of seedlings from across the latitudinal extent of black spruce in northwestern Canada provided evidence for local adaptation in black spruce seedlings; the southern seedlings accumulated biomass rapidly at the cost of risking damage to new growth from the onset of harsh temperatures, while northern seedlings grew slowly and conservatively, reducing the risk of damage at the cost of lower growth rates than their southern counterparts. We did not see any significant effect of increased CO2 concentrations on any of the seedling traits studied, however seedlings in the high nutrient treatment showed more pronounced signs of a competitive, fast-growth strategy, which ultimately led to extensive mortality of this treatment. Given this knowledge about black spruce growth dynamics in natural forests and under controlled environment conditions, I can conclude that while the mid-latitude population on a discontinuous permafrost peatland is likely to face substantial declines in productivity and forest cover loss, the northern and southern populations have the potential to remain highly productive provided evapotranspirative demands are met by precipitation, and that no major disturbances influence competitive interactions with this species

Joint effects of climate, tree size, and year on annual tree growth derived from tree-ring records of ten globally distributed forests

Tree rings provide an invaluable long-term record for understanding how climate and other drivers shape tree growth and forest productivity. However, conventional tree-ring analysis methods were not designed to simultaneously test effects of climate, tree size, and other drivers on individual growth. This has limited the potential to test ecologically relevant hypotheses on tree growth sensitivity to environmental drivers and their interactions with tree size. Here, we develop and apply a new method to simultaneously model nonlinear effects of primary climate drivers, reconstructed tree diameter at breast height (DBH), and calendar year in generalized least squares models that account for the temporal autocorrelation inherent to each individual tree\u27s growth. We analyze data from 3811 trees representing 40 species at 10 globally distributed sites, showing that precipitation, temperature, DBH, and calendar year have additively, and often interactively, influenced annual growth over the past 120 years. Growth responses were predominantly positive to precipitation (usually over ≥3-month seasonal windows) and negative to temperature (usually maximum temperature, over ≤3-month seasonal windows), with concave-down responses in 63% of relationships. Climate sensitivity commonly varied with DBH (45% of cases tested), with larger trees usually more sensitive. Trends in ring width at small DBH were linked to the light environment under which trees established, but basal area or biomass increments consistently reached maxima at intermediate DBH. Accounting for climate and DBH, growth rate declined over time for 92% of species in secondary or disturbed stands, whereas growth trends were mixed in older forests. These trends were largely attributable to stand dynamics as cohorts and stands age, which remain challenging to disentangle from global change drivers. By providing a parsimonious approach for characterizing multiple interacting drivers of tree growth, our method reveals a more complete picture of the factors influencing growth than has previously been possible

Functions of the multi-interacting protein KIDINS220/ARMS in cancer and other pathologies

Development of an organ and subsequently the whole system from an embryo is a highly integrated process. Although there is evidence that different systems are interconnected during developmental stages, the molecular understanding of this relationship is either not known or only to a limited extent. Nervous system development, amongst all, is maybe the most crucial and complex process. It relies on the correct distribution of specific neuronal growth factors and hormones to the specific receptors. Among the plethora of proteins that are involved in downstream signalling of neuronal growth factors, we find the kinase-D interacting substrate of 220 kDa (KIDINS220), also known as ankyrin-rich repeat membrane spanning (ARMS) protein. KIDINS220 has been shown to play a substantial role in the nervous system and vascular system development as well as in neuronal survival and differentiation. It serves as a downstream regulator for many important neuronal and vascular growth factors such as vascular endothelial growth factor (VEGF), the neurotrophin family, glutamate receptors and ephrin receptors. Moreover, activation and differentiation of B- and T-cells, as well as tumour cell proliferation has also shown to be related to KIDINS220. This review comprehensively summarises the existing research data on this protein, with a particular interest in its role in cancer and in other pathologies

Transposon Excision from an Atypical Site: A Mechanism of Evolution of Novel Transposable Elements

The role of transposable elements in sculpting the genome is well appreciated but remains poorly understood. Some organisms, such as humans, do not have active transposons; however, transposable elements were presumably active in their ancestral genomes. Of specific interest is whether the DNA surrounding the sites of transposon excision become recombinogenic, thus bringing about homologous recombination. Previous studies in maize and Drosophila have provided conflicting evidence on whether transposon excision is correlated with homologous recombination. Here we take advantage of an atypical Dissociation (Ds) element, a maize transposon that can be mobilized by the Ac transposase gene in Arabidopsis thaliana, to address questions on the mechanism of Ds excision. This atypical Ds element contains an adjacent 598 base pairs (bp) inverted repeat; the element was allowed to excise by the introduction of an unlinked Ac transposase source through mating. Footprints at the excision site suggest a micro-homology mediated non-homologous end joining reminiscent of V(D)J recombination involving the formation of intra-helix 3′ to 5′ trans-esterification as an intermediate, a mechanism consistent with previous observations in maize, Antirrhinum and in certain insects. The proposed mechanism suggests that the broken chromosome at the excision site should not allow recombinational interaction with the homologous chromosome, and that the linked inverted repeat should also be mobilizable. To test the first prediction, we measured recombination of flanking chromosomal arms selected for the excision of Ds. In congruence with the model, Ds excision did not influence crossover recombination. Furthermore, evidence for correlated movement of the adjacent inverted repeat sequence is presented; its origin and movement suggest a novel mechanism for the evolution of repeated elements. Taken together these results suggest that the movement of transposable elements themselves may not directly influence linkage. Possibility remains, however, for novel repeated DNA sequences produced as a consequence of transposon movement to influence crossover in subsequent generations

Kidins220/ARMS is an essential modulator of cardiovascular and nervous system development

The growth factor family of neurotrophins has major roles both inside and outside the nervous system. Here, we report a detailed histological analysis of key phenotypes generated by the ablation of the Kinase D interacting substrate of 220 kDa/Ankyrin repeat-rich membrane spanning (Kidins220/ARMS) protein, a membrane-anchored scaffold for the neurotrophin receptors Trk and p75NTR. Kidins220 is important for heart development, as shown by the severe defects in the outflow tract and ventricle wall formation displayed by the Kidins220 mutant mice. Kidins220 is also important for peripheral nervous system development, as the loss of Kidins220 in vivo caused extensive apoptosis of DRGs and other sensory ganglia. Moreover, the neuronal-specific deletion of this protein leads to early postnatal death, showing that Kidins220 also has a critical function in the postnatal brain

Neurotrophin signaling through Trk receptors : role in neuronal and cancer cell survival

Thesis (Ph. D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Microbiology and Immunology, 2008.Neurotrophin signaling through Trk receptors consists of the activation of several pathways involved in the maintenance of cellular survival as well as other normal cellular functions. While neurotrophin induced cell survival is essential for the normal development of the nervous and immune systems, it can also be considered both a therapeutic factor as well as a contributing factor to pathologic settings. In order to examine the therapeutic potential of neurotrophin signaling, we investigated the mechanism by which neurotrophins protect neurons from apoptosis. Specifically, we analyzed the effect of a Trk receptor substrate and adaptor protein, Ankyrin-rich Membrane Spanning protein (ARMS), on Nuclear Factor-κB (NF-κB) activation, a survival-promoting signal triggered by brain-derived neurotrophic factor (BDNF). Our results show that ARMS plays an important role in NF-κB signaling elicited by BDNF. Accordingly, depletion of ARMS by specific RNA interference, or disruption of ARMS-TrkB interaction with expression of dominant-negative ARMS mutant, abolished BDNF-induced signaling to NF-κB. Our data further suggests that ARMS may promote NF-κB signaling via activation of mitogen-activated kinase (MAPK) and IκB kinase (IKK), thereby facilitating phosphorylation of RelA (major NF-κB subunit) at an IKK-sensitive site. The results shown here identify ARMS as a major factor that links neurotrophin signaling to NF-κB. In an alternate approach, we examined the contribution of neurotrophin signaling to cell survival in Non-Hodgkin Lymphoma (NHL). We demonstrated that B cells derived from primary NHL tumors, as well as NHL cell lines, express Trk receptors and neurotrophin. In order to examine the potential for autocrine neurotrophin survival signaling in these cells, we exposed both primary NHL cells and cell lines to the Trk inhibitor, K252a. Our results indicate that addition of K252a abrogates proliferation of primary NHL B cells and induces apoptosis in the OCI-LY3 cell line. Investigation into the mechanism of K252 induced cell death revealed that K252a causes a subnuclear redistribution of NF-κB resulting in the inhibition of NF-κB transcriptional activity and a reduction in IL-6 production. This suggests that interference with Trk receptor signaling may be a novel strategy for treatment of NHL. Overall, our data highlights the multiple mechanisms by which neurotrophin signaling through Trk receptors can have a positive influence on cellular survival. The results presented in this thesis provide insight into how neurotrophin signaling may be targeted to provide therapy for both neurodegenerative disease and malignancy

Non-uniform growth dynamics of a dominant boreal tree species (Picea mariana) in the face of rapid climate change

Northwestern Canada’s boreal forest has experienced rapid warming, drying, and changes to permafrost, yet the growth responses and mechanisms driving productivity have been understudied at broad scales. Forest responses are largely driven by black spruce – the region’s most widespread and dominant tree. We collected tree-ring samples from four black spruce-dominated sites across 15 latitude, spanning gradients in climate and permafrost. We investigated (1) differences in growth patterns, (2) variations in climatic drivers of growth, and (3) trends in water use efficiency (WUE) throughThe presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author